Research ArticleDFT Study of Polythiophene Energy BandGap and Substitution Effects

Si Mohamed Bouzzine12 Guillermo Salgado-Moraacuten3 Mohamed Hamidi2

Mohammed Bouachrine4 Alison Geraldo Pacheco5 and Daniel Glossman-Mitnik6

1Regional Center for Trades and Professional Education annex Errachidia BP 8 52000 Meknes Morocco2Equipe drsquoElectrochimie et Environnement Faculte des Sciences et Techniques Universite Moulay IsmailBP 509 Boutalamine 52000 Errachidia Morocco3Departamento de Ciencias Quımicas Facultad de Ciencias Exactas Universidad Andres BelloSede Concepcion 4070000 Concepcion Chile4High School of Technology University Moulay Ismail Route drsquoAgouray Km 5 BP 3102 Toulal 50000 Meknes Morocco5Instituto Federal de Educacao Ciencia e Tecnologia do Sul de Minas Gerais 37576-000 Inconfidentes MG Brazil6Laboratorio Virtual NANOCOSMOS Departamento de Medio Ambiente y Energıa Centro de Investigacionen Materiales Avanzados 31136 Chihuahua CHIH Mexico

Correspondence should be addressed to Daniel Glossman-Mitnik danielglossmancimavedumx

Received 2 March 2015 Revised 23 April 2015 Accepted 29 April 2015

Academic Editor Rocıo Sanchez-de-Armas

Copyright copy 2015 Si Mohamed Bouzzine et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Polythiophene (PTh) and its derivatives are polymer-basedmaterials with a 120587-conjugation framework PTh is a useful photoelectricmaterial and can be used in organic semiconductor devices such as PLED OLED and solar cells Their properties are based onmolecular structure the derivatives contain different substitutes in the 3 and 5 positions such as electron-donating or electron-withdrawing groups All molecular geometries were optimized at B3LYP6-31G(dp) level of theoryThe energy gap (119864gap) betweenthe HOMO and LUMO levels is related to the 120587-conjugation in the PThpolymer backbone In this study the DFT calculations wereperformed for the nonsubstituted and 35-substituted variants to investigate the stability geometries and electrical properties Thetheoretical calculations show that the substituted forms are stable have low 119864gap and are in good agreement with the experimentalobservations

1 Introduction

Conjugated polymers are of considerable interest due to theirelectronic properties and their potential technological appli-cations [1] They have many advantages compared to inor-ganic semiconductors such as easy processing and tunableoptical gaps Their electronic properties are determined bythe delocalized 120587-electrons along their carbon backbone [2]Polythiophene is themost important conjugated polymer uti-lized in a broad spectrum of applications such as conductingpolymers light-emitting diodes field effect transistors andplastic solar cells due to its excellent optical and electricalproperties as well as exceptional thermal and chemicalstability Early syntheses of poly(3-alkythiophene) involved

chemical oxidation or electrochemical polymerization in thepursuit of soluble and processable polythiophenes [3ndash5]However these processes suffered from the major problemthat the structure of the polymer is somewhat uncertain andundefined [6 7] As 3-alkylthiophene is an asymmetric mole-cule there are three possible orientations available whenthe two thiophene rings are coupled between the 2 and 5positionsThe first of these is the 2-51015840 or head-to-tail coupling(HT)The second is 2-21015840 or head-to-head coupling (HH) andthe third is 5-51015840 or tail-to-tail coupling (TT) (see Figure 1)

Polythiophene (PTh) and its derivatives are used in sev-eral applications such as displays electromagnetic shieldingand molecular electronics [8] and due to them being ther-mally stable at ambient temperatures have been used in new

Hindawi Publishing CorporationJournal of ChemistryVolume 2015 Article ID 296386 12 pageshttpdxdoiorg1011552015296386

2 Journal of Chemistry

S S

RR

S S

RR

S S

RR

44

4

Head-to-tail (HT) Head-to-head (HH)

8TCOC (HT)

8TCOC (HH)8TOC (HT)

8TOC (HH)

8TCOC (TT)

8TOC (TT)

S S

RR

4

Tail-to-tail (TT) Tail-to-tail (TT)

8TOOC

8T

RR

R = COC

R = OC R = COC

R = OC

R = COC

R = OC

R = OOC

R = H

di

120579i

di

120579i

di

120579i

di

120579i

Figure 1 Sketch map of the structures length bond and dihedral angle

optical devices such as surface light-emitting diodes (SLED)and light-emitting diodes (LED) [9] One of the main goalsin the field of electrically conducting polymers is to developa complete understanding of the relationship between thechemical structure of the polymer and its electronic andconduction properties Once such an insight is achieved thedesired electronic properties could be obtained by specificsynthesis following molecular design The conduction prop-erties of an undoped polymer in terms of the band theoryof solids are known to be related to its electronic propertiessuch as the ionization potential (IP) electronic affinity (EA)and band gap (119864gap) [10] The key factor that determinesthe intrinsic properties of the polythiophene variants is theirband structures particularly the positions of the conductionand valence bands and the gap between them Thereforethe 120587-electrons in conducting polymers play a major role indetermining their electrical conductivity and band structure[11] The energy between the valence and conduction band ofa polymer is related to the lowest energy of its monomer unitsand to the bandwidth resulting from the overlap between themonomer orbitals [12] A band gap is defined as the differencebetween the highest occupied molecular orbital (HOMO)and the lowest unoccupiedmolecular orbital (LUMO) energylevels in the polymer [13]

119864gap = 119864LUMO minus 119864HOMO (ev) (1)

So the electrical conductivity is directly related to the HOMOand LUMO energy of the molecule

2 Methods Computational Details

Full geometry optimizations were performed under no con-straints in the framework of the density functional theory(DFT) by means of the B3LYP functional [the Becke3 and

the LeeminusYangminusParr hybrid functional] using the Gaussian09 program [14] The 6-31G(dp) basis set was chosen as acompromise between the quality of the theoretical approachand the high computational cost associated with the highnumber of dimensions to the problem [15 16]

The HOMO LUMO and energy gaps were also deducedfrom the stable structure of the nonsubstituted forms In thispaper the transition energies were calculated at the groundstate geometries using TD-DFTB3LYP calculations and theresultswere comparedwith the available experimental data Anewly designed function the long-range Coulomb-attenua-ting method (CAM-B3LYP) considered long-range interac-tions by comprising 19 of HF and 81 of B88 exchangeat short range and 65 of HF plus 35 of B88 at longrange [17] Furthermore the CAM-B3LYP method has beenapplied and was found to be reasonably capable of predictingthe excitation energies and the absorption spectra of themolecules [18ndash21] Therefore the vertical excitation energyand electronic absorption spectra were simulated using theTD-CAM-B3LYP method in this work The investigatedpolymers 8T 8TCOO and 8TOC (HH HT and TT) and8TCOC (HH HT and TT) are depicted in Figure 1

3 Results and Discussion

31 Geometric Properties For all molecules geometricalparameters were obtained after total optimization by B3LYP6-31G(dp) To investigate the effect of the substituents on thegeometries and electronic properties the optimized struc-tures of several substituted oligomers built on thiophene8TOOC 8TCOC (HH HT and TT) and 8TOC (HH HTand TT) are compared with the unsubstituted one 8T On theother hand to investigate the effects of different regioregulari-ties (HH HT and TT) are compared between them and with

Journal of Chemistry 3

Table 1 Values of interring bond lengths 119889119894(A) of the studied

compounds obtained by B3LYP6-31G(dp) level

Compounds 1198891119889211988931198894119889511988961198897

8T 1445 1441 1440 1440 1440 1441 1445

8TOCHT 1441 1435 1434 1433 1434 1435 1439HH 1445 1434 1438 1432 1438 1434 1445TT 1439 1438 1432 1437 1432 1438 1439

8TCOCHT 1451 1447 1446 1446 1446 1447 1451HH 1449 1456 1446 1454 1446 1454 1448TT 1459 1446 1455 1446 1455 1446 1459

8TOOC 1442 1439 1438 1438 1438 1439 1442

Table 2 Values of dihedral angle 120579119894(∘) of the studied compounds

obtained by B3LYP6-31G(dp) level

Compounds 1205791120579212057931205794120579512057961205797

8T 17996 17996 17996 17996 17996 17996 17996

8TOCHT 180 180 180 180 180 180 180HH 16149 17996 17017 17969 16986 17998 16151TT 180 180 180 180 180 180 180

8TCOCHT 14637 15518 15694 15419 15729 15234 14824HH 16504 12617 17670 13204 17143 13092 16230TT 12247 17057 12790 16860 12790 17060 12247

8TOOC 17585 17714 17593 17873 17992 17962 17997

the 8T and 8TOOC compounds The geometric characteris-tics given as interring distances (119889

119894) and dihedral angle (120579

119894)

are listed in Tables 1 and 2The optimized structures (see Figure 4) of compounds

(8TCOOC and 8TOC with different regioregularities) arecompared with each other and also with 8T and 8TOOCThegeometric characteristics are given as interring distances (119889

119894)

and used to investigate the effect of different regioregularities(HT HH and TT)The theoretical calculations show that thetorsional angles are evaluated to be about asymp180∘ (a quasi-planar conformation) for 8T and 8TOC (HT and TT confor-mations) whereas the other compounds show an antigaucheangle with an average twist angle between 122∘ and 170∘ for8TCOC (HH and TT) and the 8TCOC (HT) shows the valueof torsion angle between the values of 8TCOC (HH and TT)of about 150∘ (see Tables 1 and 2 and Figures 2 and 3)

The properties of the oligomer for 8TOC (HT and TT)can be explained by the effects of the OCH

3donor group

compared with the CH2-OCH

3groupThe electronic doublet

of the methoxy group increases the conjugation whichpromotes better flatness of the system in contrast to theCH2OCH3groupThese results are audited by the intercyclic

study of the values of the bindings This shows that in goingfrom the 8T compound to 8TOOC and 8TOC (HH TT andHT) compounds there is a reduction of the values of theinterring bindings (see Tables 1 and 2 and Figures 2 and 3)These results may be explained by a repulsion of the OOCH

3

(8TOOC) andOCH3(8TOC) groups among them that favors

the flatness of these systems The comparison of the valuesof the bindings of intercyclic 8T compounds with 8TCOC

shows an increase of these values for those systems withantigauche torsion angles and indicates the strong interaction(attraction) of the CH

2OCH3groups among them

32 Electronic Parameters Table 3 lists the theoretical elec-tronic parameters of the studied conjugated compoundsThecalculated electronic parameters (119864gap LUMO and HOMO)of compounds 8T 8TCOC (HH HT and TT) 8TOOC and8TOC (HH HT and TT) exhibit the destabilization of theHOMO and LUMO levels in comparison with those of theunsubstituted one (8T) due to electron-donating substitutiongroups while in the case of 8TOC there is a net stabilizationof the HOMO and LUMO levels However these compoundshave a smaller energy gap (119864gap) than the unsubstituted onewhich is due to the presence of a methoxy group in the 120573position of the thiophene ring The band gap of 8TOC ismuch smaller than that of the other substituted compoundsThis may be attributed to the number of electron-donatingmethoxy side groups and also to the Coulombic interactionbetween the sulfur of thiophene and oxygen atoms [27 28]The theoretical band gaps computed for isolated chains areexpected to be about 02 eV larger than the values computedin the condensed phase [29] When taking into account thisdifference the band gap values obtained are close to theexperimental data for the octamerThe value of the octamerrsquos8T and 8TOC band gap (222 eV and 193 eV resp aftercorrection) is in accordance with that measured experiment-ally for polythiophene 20ndash23 eV [30 31] and that forpoly(441015840-dimethylbithiophene (8TOC (TT))) was estimatedto be 16 eV [23] The octamer seems to be a useful model toobtain a better understanding of the electronic properties ofthe polymeric system

It is important to examine the HOMO and the LUMOenergies for these oligomers because the relative ordering ofthe occupied and virtual orbital provides a reasonable quali-tative indication of excitation properties In general as shownin Figure 5 (LUMOHOMO) theHOMOs of these oligomerspossess a 120587-bonding character within a subunit and a 120587-antibonding character between the consecutive subunits Onthe other hand the LUMOs possess a 120587-antibonding charac-ter within a subunit and a 120587-bonding character between thesubunits The experiment shows that the HOMO and LUMOenergies are obtained from an empirical formula based onthe onset of the oxidation and reduction peaks measured bythe cyclic voltammetry In theory the HOMO and LUMOenergies can be calculated by the DFT calculation [32 33]However it is noticeable that solid-state packing effects arenot included in the DFT calculations which tend to affectthe HOMO and LUMO energy levels in a thin film comparedwith an isolated molecule as considered in the calculationsEven if these calculated energy levels are not accurate it ispossible to use them to obtain the information by comparingsimilar oligomers or polymers The calculated electronicparameters (Gap HOMO and LUMO) of compounds 8T8TOOC 8TOC (HH HT and HT) and 8TCOC (HH HTand HT) are illustrated in Table 3

In the case of compounds 8TOC 8TOOC and 8TCOCit is notable that there is a systematic change of the HOMOand LUMO energies into the backbone substitution raises

4 Journal of Chemistry

1 2 3 4 5 6 71438

1439

1440

1441

1442

1443

1444

1445

1446

Bond number Bond number

8T8TOOC

1 2 3 4 5 6 7

1440

1444

1448

1452

1456

1460

8T8TCOC (HT)

8TCOC (TT)8TCOC (HH)

1 2 3 4 5 6 7

1432

1434

1436

1438

1440

1442

1444

1446

Bond number

8T8TOC (HT)

8TOC (HH)8TOC (TT)

Valu

es o

f len

gth

bond

(Aring)

Valu

es o

f len

gth

bond

(Aring)

Valu

es o

f len

gth

bond

(Aring)

Figure 2 Optimized C-C bond lengths interring of 8T 8TOOC 8TCOC (HH HT and TT) and 8TOC (HH HT and TT) in neutral stateswith the number of bonds studied by B3LY6-31G(dp) level

Table 3 Energy values of 119864LUMO (eV) 119864HOMO (eV) 119864gap (eV) and the open circuit voltage 119881oc (eV) of the studied molecules

Compounds 119864HOMO (eV) 119864LUMO (eV) 119864gap (eV) 119864gap (eV) exp 119881oc (eV)8T minus473 minus231 242 200 [22] 073

8TOOC minus416 minus170 246 016

8TCOC(HT) minus462 minus196 266 062(HH) minus490 minus188 302 090(TT) minus491 minus181 310 091

8TOC(HT) minus387 minus196 191 mdash(HH) minus389 minus182 207 mdash(TT) minus399 minus186 213 16 [23] mdash

PCBM [24 25] minus610 minus370

or lowers the HOMOLUMO energies in agreement withtheir electron donor character However these compoundshave a smaller energy gap (119864gap) than the unsubstituted one(8T) which is due to the presence of different substituents

as described previously [34 35] The band gap of 8TOC(HH TT and HT) is much smaller than that of the othersubstituted compoundsThismay be attributed to the numberof electron-donating methoxy side groups

Journal of Chemistry 5

1 2 3 4 5 6 7

120

130

140

150

160

170

180

190

200

210

Angle number Angle number

8T8TCOC (HT)

8TCOC (HH)8TCOC (TT)

1 2 3 4 5 6 7160

165

170

175

180

185

190

195

200

8T8TOC (HT)

8TOC (HH)8TOC (TT)

Valu

es o

f dih

edra

l ang

le (∘

)

Valu

es o

f dih

edra

l ang

le (∘

)

Figure 3 Optimized dihedral angle of 8T 8TCOC (HH HT and TT) and 8TOC (HH HT and TT) in neutral states with the number ofbonds studied by B3LY6-31G(dp) level

8T 8TOOC

8TCOC (HT) 8TCOC (TT)

8TCOC (HH)

8TOC (HT) 8TOC (HH)

8TOC (TT)

Figure 4 Optimized structures of the studied oligomers

6 Journal of Chemistry

HOMO LUMO

8T

8TOOC

8TOC (HT)

8TOC (TT)

8TOC (HH)

8TCOC (HT)

8TCOC (TT)

8TCOC (HH)

Figure 5 The contour plots of HOMO and LUMO orbitals of the studied compounds

33 Photovoltaic Properties Generally the most efficientpolymer solar cells are based on the bulk heterojunction(BHJ) structure of the blend of 120587-conjugated polymer donorsand fullerene derivative acceptors [7 36ndash40] Here we stud-ied the photovoltaic properties of polyalkyl thiophene with

[66]-phenyl-C61-butyric acidmethyl ester (PCBM) which isthe most widely used acceptor in solar cell devices The cor-responding structure of the photovoltaic devices is schemat-ically depicted in Figure 6 The difference in the HOMOenergy levels of 8T 8TCOC 8TOOC and the LUMO of

Journal of Chemistry 7En

ergy

(eV

)

HOMO

LUMO

minus65

minus60

minus55

minus50

minus45

minus40

minus35

minus30

minus25

minus20

minus15

PCBM

(C60

)

8TO

C (T

T)

8TO

C (H

T)

8TO

C (H

H)

8TCO

C (T

T)

8TCO

C (H

H)

8TCO

C (H

T)

8TO

OC8T

Voc

Egap

Figure 6 Band structure diagram illustrating the HOMO andLUMO energies of the studied compounds relative to the bandstructure of PCBM

PCBM was 073 eV 016 eV and 062 eV respectively butthe value of 8TOC is negative (Table 3) suggesting that thephotoexcited electron transfer from the study compounds toPCBM may be sufficiently efficient to be useful in photo-voltaic devices [24 41 42]

In principle the optimization of polymer-fullerene solarcells is based on fine-tuning the electronic properties andinteractions of the donor and acceptor components so as toabsorb themaximumquantity of light and generate the great-est number of free charges with minimal concomitant loss ofenergy and transport the charges to the electrodes Howeverit is necessary to know the ideal electronic characteristics thateach component should have for the design of the next gen-eration high-efficiency photovoltaic systems The two com-ponents required in these devices for electronic optimizationare a soluble fullerene (generally a C60 derivative) acceptorand a polymeric donor that can be processed in solutionFullerenes are currently considered to be the ideal acceptorsfor organic solar cells for several reasons First they have anenergetically deep-lying LUMO which endows the moleculewith a very high electron affinity relative to the numerouspotential organic donors [25]

It is apparent that the active layer donor-acceptor com-posite governs all aspects of the mechanism with theexception of charge collection which is based on the elec-tronic interface between the active layer composite and therespective electrode Besides the fundamental mechanisticsteps the open circuit voltage (119881oc) is also governed by theenergetic relationship between the donor and the acceptor(Figure 6) rather than the work functions of the cathode andanode as would be expected from a simplistic view of thesediode devices Specifically the energy difference between theHOMO of the donor and the LUMO of the acceptor is foundto be very closely correlated with the 119881oc value [43ndash45]

The maximum open circuit voltage (119881oc) of the BHJ solarcell is related to the difference between the highest occupiedmolecular orbital (HOMO) of the electron donor and theLUMO of the electron acceptor taking into account theenergy lost during the photocharge generation [46] The the-oretical values of open circuit voltage119881oc have been calculatedfrom the following expression

119881oc =10038161003816100381610038161003816119864HOMO

(Donor)10038161003816100381610038161003816minus

10038161003816100381610038161003816119864LUMO

(Acceptor)10038161003816100381610038161003816minus 03 (2)

Moreover these compounds have absorption maxima in theneighborhood of 400ndash540 nm (Table 4) which is the opti-mum range of absorption (UV-visible) for photovoltaic cellsIn addition they have an energy gap of the order of 200 eV(Table 3) for the elevation of the electron from the HOMO tothe LUMO orbitals This characteristic allows us to promotethese compounds for the production of solar cells Thesevalues are sufficient for a possible efficient electron injectionsystem Therefore all the studied molecules can be used asorganic solar cell components because the electron injectionprocess from the excited molecule to the conduction bandof the acceptor (PCBM) and the subsequent regeneration ispossible in photovoltaic cells

4 Optoelectronic Parameters

41 Electronic Absorption Spectra For a better understandingof the electronic properties of thiophene-based moleculesthe excitation energy based on the first and second singlet-singlet electronic transitions has been studied In recentyears time dependent density functional theory (TD-DFT)has emerged as a reliable standard tool for the theoreticaltreatment of electronic excitation spectra and recent worksdemonstrate better accuracy for a wide range of systems [4748] The TD-DFTB3LYP6-31G(dp) has been used on thebasis of the optimized geometry The nature and the energyof the singlet-singlet electronic transitions of all the oligomersin all series under study are reported in Table 4 All electronictransitions are 120587 rarr 120587lowast type and no localized electronictransitions are exhibited among the calculated singlet-singlettransition Table 4 summarizes the transition energies ofabsorption spectra and oscillator strength Two interestingtrends in oscillator strength can be found in all series ofcompounds the oscillator strength OS of 119878

0rarr 1198781is the

overwhelmingly largest of all the series of polymersAccording to Table 4 we note an excitation energy of

about 2 eV for all compounds studied In addition absorp-tion maxima were located in the 400ndash540 nm range for allcompounds indicating all molecules have only one band inthe visible region (120582abs gt 400 nm) The absorption spectra ofthese compounds showed a major absorption band assignedto the 120587 rarr 120587lowast transition local electron

According to the transition character most of the com-pounds show the HOMOrarr LUMO transition as the firstsinglet excitationThemaximum (120582max) wavelengths for UV-vis absorption spectra of all compounds simulated are shownin Figure 7 The calculated 120582max by TD-DFT-B3LY and TD-CAM-B3LYP is different by about 99 nm = 120582max(B3LYP) minus120582max(CAM-B3LYP)

8 Journal of Chemistry

Table 4 Excitation energy valuesΔ119864 for the studied compounds obtained by TD-DFTCAM-B3LYP TD-DFT B3LYPwith 6-31G (dp) level

Compounds 120582 (nm) Exp [26] TD-B3LYP TD-CAM-B3LYP (DMSO) TD-CAM-B3LYP120582 (nm) 119864 (eV) (OS) 120582 (nm) 119864 (eV) (OS) 120582 (nm) 119864 (eV) (OS) Molecular orbital

8T 44864459 192 (29063) 49362 251 (30912) 47807 259 (29578)

Hrarr L (063)55329 224 (0000) 41015 302 (0000) 39233 310 (00000)53639 231 (0000) 32315 383 (0000) 32300 383 (00000)

8TOC

HT71723 172 (14020) 54514 227 (32032) 52971 234 (29449)

Hrarr L (064)55736 222 (16056) 43788 283 (00002) 42071 294 (00021)51485 240 (00072) 36582 338 (02814) 36469 339 (02123)

HH66172 187 (28471) 56823 218 (31391) 54455 227 (30037)

Hrarr L (064)465 55155 224 (0000) 45348 273 (0000) 43004 288 (0000)45297 273 (0000) 36233 342 (0000) 36074 343 (0000)

TT64658 191 (28253) 55533 223 (30750) 53332 232 (29676)

Hrarr L (064)53795 230 (0000) 44230 280 (00041) 42118 294 (00035)

47532 260 (0000) 35593 348(00004) 35462 349 (00001)

8TCOC

HT52952 234 (24562) 45023 275 (25260) 43961 282 (28030)

Hrarr L (062)44536 278 (00966) 38134 325 (00568) 36861 336 (00488)42203 293 (00397) 33152 373 (03015) 32230 384 (02428)

HH47208 262 (21440) 40435 306 (26989) 39618 312 (25865)

Hrarr L (062)mdash 40834 303 (00008) 35682 347 (00998) 34623 358 (00852)

39627 312 (00661) 31908 388 (02093) 28581 433 (00000)

TT46712 265 (20300) 41163 301 (27553) 39282 315 (24701)

Hrarr L (062)40397 306 (00042) 36159 342 (00509) 34187 362 (00641)39818 311 (00434) 32429 382 (03900) 31340 395 (04098)

8TOOC mdash57329 216 (26859) 48934 253 (30704) 47422 261 (29274)

Hrarr L (064)47995 258 (0000) 40835 305 (0000) 39248 315 (00001)44588 278 (0000) 34835 355 (02826) 33704 367 (02340)

The prediction of the excitation energies and oscillatorstrengths by using the CAM-B3LYP is in better agreementwith the experimental results [49 50] than is found forB3LYP because the CAM- (Coulomb-attenuating method-)B3LYP also takes account of the long-range corrections fordescribing the long 120587-conjugation [51]The results are shownin Table 4 and we note that the excitation energy values Δ119864obtained by TD-DFTCAM-B3LYP6-31G(dp) level are inagreement with those obtained by the methods DFTB3LYP6-31G(dp) level therefore theCAM-B3LYP functional is veryuseful for predicting the excitation energies and oscillatorstrengths The values calculated using the TD-DFT CAM-B3LYP function of our compounds in vacuo for predictingthe excitation energies and oscillator strengths are listed inTable 4 The TDCAM-B3LYP6-31G(dp) method was alsoemployed to simulate the optical property of the compounds

42 Effect of Solvent Solvent effects attract considerable atte-ntion because most of the chemical processes occur in thesolution phaseThe solvent effects are included here to ensure

that the calculations are compatible with the typical con-ditions The effects of chemical environment are discussedfurther as follows In order to study the effect of solvents onthe ground state molecular geometry excitation energies andmaximum absorption quantum chemical calculations on thestudied molecules were carried out in vacuum in dimethylsulfoxide (DMSO) The longest wavelength peaks from C-PCM-TD-CAM-B3LYP6-31G(dp) results are shifted com-pared to the corresponding ones using the TD-CAM-B3LYPresults The magnitudes of the spectral shifts are about 15 nmfor 8T 8TOC (HT) and 8TOOC and 1881 2201 2368 817and 1062 nm for 8TCOC (TT) 8TOC (TT) 8TOC (HH)8TCOC (HH) and 8TCOC (HT) respectively The absorp-tionmaxima of all compounds are further shifted by the effectof the dimethyl sulfoxide solventThis might be related to thegradient electrostatic potential and donor effect of the OCH

3

CH2OCH3 and OOCH

3groups Further there is a variation

of the absorption maximum displacement for the samecompound (HT TT andHH) this is the result of the differentconfigurations that one compound can take In DMSO

Journal of Chemistry 9

200 300 400 500 600 700 800 900 1000 1100

0

20000

40000

60000

80000

100000

120000

140000

8TAbEm

200 300 400 500 600 700 800 900 1000 1100

0

20000

40000

60000

80000

100000

120000

140000

8OOCAbEm

120582 (nm) 120582 (nm)

Ener

gy (a

u)

Ener

gy (a

u)

Δ120582

200 300 400 500 600 700 800 900 1000 1100

0

20000

40000

60000

80000

100000

120000

140000

AbsorptionEmission

8TCOCHHabHHemHTab

HTemTTabTTem

300 400 500 600 700 800 900 1000 1100 1200 1300

0

20000

40000

60000

80000

100000

120000Absorption Emission

8TCOHHabHHemHTab

HTemTTabTTem

120582 (nm) 120582 (nm)

Ener

gy (a

u)

Ener

gy (a

u)

Figure 7 Calculated electronic absorption and emission of octamers units of 8T 8TOC (HH HT and TT) 8TOOC and 8TCOC (HH HTand TT) obtained by CAM-B3LYP6-31G(dp)

the calculated results for the absorptionmaximumof all com-pounds are located between 56823 and 40435 nm (Table 4)The peak positions of those molecules in DMSO show a redshift when compared to those measured experimentally [26]

43 Electronic Emission Spectra TD-DFTB3LYP6-31G(dp)has been used for optimized structures and CAM-B3LYP6-31G(dp) was used to calculate the excited state and to sim-ulate the emission spectra of the considered polymers andthe first singlet excited states are listed in Table 5 Similar tothe absorption spectra 119878

1rarr 1198780fluorescence peaks in emi-

ssion spectra (Figure 6) have the greatest oscillator strengthsin all molecules and exclusively arise fromHOMOrarr LUMO(120587 rarr 120587lowast electronic transition) Polymers with aromatic orheterocyclic units generally absorb light with wavelengths in

the range from 300 to 700 nm due to 120587 rarr 120587lowast transitionsThe excited states of their chromophores (excitons) releaseenergy radiatively as well as nonradiatively on returning tothe ground state [26] The radiative decay of excitons to theground state can emit visible light These excitons are alsoformed when a bias potential is applied to an emissive poly-mer sandwiched between an anode and a cathode [52]

The theoretical studies of our molecules can be used toderive the Stokes shifts the difference between the positionof the maxima band of the absorption and emission spectrain wavelength which is about 80 to 93 nm for the structures8T 8TOC (HH TT and HT) 8TCOC (TT) and 8TOOCbut that for the 8TCOC (HH) and 8TCOC (TT) is 149 nmAmong them the compound 8TCOC has a relatively largerStokes shift which indicates that electron transitions break

10 Journal of Chemistry

Table 5 Emission spectra in gaseous phase obtained by the TD-CAM-B3LYP6-31G(d) optimized geometries of 119878

1excited states for

the octamers

Compounds 120582 (nm) 119864 (eV) OS Δ120582 = 120582ab minus 120582em55797 222 30531

8T 43390 285 00000 79836564 339 00000

8TOC

HT62147 199 29482

817646113 268 0005742181 293 02710

HH63709 196 30801

925446191 268 0000040654 304 00000

TT62147 199 29482

881546113 268 0005742181 293 02710

8TCOC

TT53079 233 26028

911840043 309 0035434914 355 03253

HH54518 247 27840

1490040748 304 0027535560 348 00001

HT56951 217 30310

1766942626 290 0000136784 337 0007956106 220 29875

8TOOC 42641 290 00002 868436421 340 00000

the strong conjugate effect leading to remarkable changes inthe structure and reorganization energy as discussed above

5 Conclusions

In this study we have used the DFTB3LYP method to inves-tigate the theoretical analysis of the geometries and electronicproperties of some type-in-derivatives structure of polythio-phene The modification of chemical structures can greatlymodify and improve the electronic and optical properties ofpristine studied materials The electronic properties of theconjugated materials based on thiophene compounds havebeen computed using the 6-31G(dp) basis set at a densityfunctional B3LYP level in order to guide the synthesis ofnovel materials with specific electronic properties

In summary the conclusions are as follows

(i) TheUV-vis absorption properties have been obtainedby using TDCAM-B3LYP and TD-B3LYP calcula-tions The obtained absorption maximums are in therange of 350ndash550 nm

(ii) The HOMO level LUMO level and band gap ofthe studied compounds were well controlled by theacceptor strength The calculated band gap (119864gap) ofthe studiedmolecules was in the range of 191ndash302 eV

(iii) The calculated values of 119881oc of the studied moleculesrange from 016 eV to 091 eVPCBM these values aresufficient for a possible efficient electron injection

The theoretical results suggest that both the donor strengthand the stable geometry contribute significantly to the elec-tronic properties of the conjugated polymers Finally the pro-cedures of theoretical calculations can be employed to predictthe electronic properties of the other compounds and furtherto design novel materials for organic solar cells

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work has been supported by the Volubilis Program(no MA11248) and the convention CNRSTCNRS (ProjectChimie 1009) The authors are grateful to the ldquoAssociationMarocaine des Chimistes Theoriciensrdquo (AMCT) for its per-tinent help Guillermo Salgado-Moran gratefully acknowl-edges Si Mohamed Bouzzine for his invitation to participatein this work Daniel Glossman-Mitnik is a researcher ofCIMAV and CONACYT and acknowledges both institutionsfor partial support

References

[1] H-J Wang C-P Chen and R-J Jeng ldquoPolythiophenes com-prising conjugated pendants for polymer solar cells a reviewrdquoMaterials vol 7 no 4 pp 2411ndash2439 2014

[2] S Pesant P Boulanger M Cote and M Ernzerhof ldquoAb initiostudy of ladder-type polymers polythiophene and polypyrrolerdquoChemical Physics Letters vol 450 no 4ndash6 pp 329ndash334 2008

[3] J Roncali ldquoConjugated poly(thiophenes) synthesis functional-ization and applicationsrdquo Chemical Reviews vol 92 no 4 pp711ndash738 1992

[4] Y Wei C-C Chan J Tian G-W Jang and K F HsuehldquoElectrochemical polymerization of thiophenes in the presenceof bithiophene or terthiophene kinetics and mechanism of thepolymerizationrdquo Chemistry of Materials vol 3 no 5 pp 888ndash897 1991

[5] R M Souto Maior K Hinkelmann H Eckert and FWudl ldquoSynthesis and characterization of two regiochemi-cally defined poly(dialkylbithiophenes) a comparative studyrdquoMacromolecules vol 23 no 5 pp 1268ndash1279 1990

[6] M-A Sato and H Morii ldquoNuclear magnetic resonance stud-ies on electrochemically prepared poly(3-dodecylthiophene)rdquoMacromolecules vol 24 no 5 pp 1196ndash1200 1991

[7] Y-J Cheng S-H Yang and C-S Hsu ldquoSynthesis of conjugatedpolymers for organic solar cell applicationsrdquo Chemical Reviewsvol 109 no 11 pp 5868ndash5923 2009

[8] A C AlgunoW C Chung R V Bantaculo et al ldquoAb initio anddensity functional studies of polythiophene energy band gaprdquoNECTEC Technical Journal vol 2 no 9 pp 215ndash218 2001

[9] J Pei W-L Yu W Huang and A J Heeger ldquoA novel series ofefficient thiophene-based light-emitting conjugated polymersand application in polymer light-emitting diodesrdquo Macro-molecules vol 33 no 7 pp 2462ndash2471 2000

Journal of Chemistry 11

[10] A K Bakhshi ldquoTheoretical tailoring of electrically conductingpolymers some new resultsrdquoMaterials Science and EngineeringC vol 3 no 3-4 pp 249ndash255 1995

[11] M S Senevirathne A Nanayakkara and G K R Senadeera ldquoAtheoretical investigation of band gaps of conducting polymersmdashpolythiophene polypyrrole and polyfuranrdquo inProceedings of the23rd Technical Sessions vol 23 pp 47ndash53 Institute of PhysicsColombo Sri Lanka March 2007

[12] U Salzner J B Lagowski P G Pickup and R A PoirierldquoDesign of low band gap polymers employing density func-tional theorymdashhybrid functionals ameliorate band gap prob-lemrdquo Journal of Computational Chemistry vol 18 no 15 pp1943ndash1953 1997

[13] E Bundgaard and F C Krebs ldquoLow band gap polymers fororganic photovoltaicsrdquo Solar Energy Materials and Solar Cellsvol 91 no 11 pp 954ndash985 2007

[14] M J Frisch G W Trucks H B Schlegel et al ldquoGaussian 09Revision B04rdquo Gaussian Inc Wallingford Conn USA 2009

[15] M E Casida C Jamorski K C Casida and D R SalahubldquoMolecular excitation energies to high-lying bound states fromtime-dependent density-functional response theory charac-terization and correction of the time-dependent local den-sity approximation ionization thresholdrdquo Journal of ChemicalPhysics vol 108 no 11 pp 4439ndash4449 1998

[16] R E Stratmann G E Scuseria and M J Frisch ldquoAn efficientimplementation of time-dependent density-functional theoryfor the calculation of excitation energies of largemoleculesrdquoTheJournal of Chemical Physics vol 109 no 19 pp 8218ndash8224 1998

[17] T Yanai D P Tew and N C Handy ldquoA new hybrid exchange-correlation functional using the Coulomb-attenuating method(CAM-B3LYP)rdquo Chemical Physics Letters vol 393 no 1ndash3 pp51ndash57 2004

[18] J Preat ldquoPhotoinduced energy-transfer and electron-transferprocesses in dye-sensitized solar cells TDDFT insights fortriphenylamine dyesrdquoThe Journal of Physical Chemistry C vol114 no 39 pp 16716ndash16725 2010

[19] B Camino M de La Pierre and A M Ferrari ldquoPhotoelectro-chemical properties of the CT1 dye a DFT studyrdquo Journal ofMolecular Structure vol 1046 pp 116ndash123 2013

[20] A Irfan R Jin A G Al-Sehemi and A M Asiri ldquoQuantumchemical study of the donor-bridge-acceptor triphenylaminebased sensitizersrdquo Spectrochimica Acta Part A Molecular andBiomolecular Spectroscopy vol 110 pp 60ndash66 2013

[21] S Jungsuttiwong R Tarsang T Sudyoadsuk V Promarak PKhongpracha and S Namuangruk ldquoTheoretical study on noveldouble donor-based dyes used in high efficient dye-sensitizedsolar cells the application of TDDFT study to the electroninjection processrdquoOrganic Electronics PhysicsMaterials Appli-cations vol 14 no 3 pp 711ndash722 2013

[22] E J Meijer D M de Leeuw S Setayesh et al ldquoSolution-processed ambipolar organic field-effect transistors and invert-ersrdquo Nature Materials vol 2 no 10 pp 678ndash682 2003

[23] V Hernandez J T L Navarrete and J L Marcos ldquoElectronicstructure and lattice dynamics of polyfuranrdquo Synthetic Metalsvol 41 no 3 pp 789ndash792 1991

[24] F B Kooistra J Knol F Kastenberg et al ldquoIncreasing the opencircuit voltage of bulk-heterojunction solar cells by raising theLUMO level of the acceptorrdquo Organic Letters vol 9 no 4 pp551ndash554 2007

[25] J J M Halls J Cornil D A dos Santos et al ldquoCharge- andenergy-transfer processes at polymerpolymer interfaces a joint

experimental and theoretical studyrdquo Physical Review B vol 60no 8 pp 5721ndash5727 1999

[26] M Fall J-J Aaron and D Gningue-Sall ldquoLuminescence prop-erties of poly(3-methoxythiophene)mdashbithiophene compositeoligomersrdquo Journal of Fluorescence vol 10 no 2 pp 107ndash1112000

[27] M Cossi N Rega G Scalmani and V Barone ldquoEnergiesstructures and electronic properties of molecules in solutionwith the C-PCM solvation modelrdquo Journal of ComputationalChemistry vol 24 no 6 pp 669ndash681 2003

[28] V Barone and M Cossi ldquoQuantum calculation of molecularenergies and energy gradients in solution by a conductor solventmodelrdquoThe Journal of Physical Chemistry A vol 102 no 11 pp1995ndash2001 1998

[29] J F Pan S J Chua and W Huang ldquoQuantum calculationof molecular energies and energy gradients in solution by aconductor solventmodelrdquoChemical Physics Letters vol 363 no1-2 pp 18ndash24 2002

[30] U Salzner J B Lagowski P G Pickup and R A Poirier ldquoCom-parison of geometries and electronic structures of polyacety-lene polyborole polycyclopentadiene polypyrrole polyfuranpolysilole polyphosphole polythiophene polyselenophene andpolytellurophenerdquo Synthetic Metals vol 96 no 3 pp 177ndash1891998

[31] A Kraak and H Wynberg ldquoCharge-transfer interaction ofdithienyls and cyclopentadithiophenes with 135-trinitroben-zene (TNB)rdquo Tetrahedron vol 24 no 10 pp 3881ndash3885 1968

[32] M Dietrich and J Heinze ldquoPoly(441015840-dimethoxybithiophe-ne)mdasha new conducting polymer with extraordinary redox andoptical propertiesrdquo SyntheticMetals vol 41 no 1-2 pp 503ndash5061991

[33] H Zgou M Hamidi M Bouachrine and K Hasnaoui ldquoTheDFT study and opto-electronic properties of copolymers basedon thiophene and phenylenerdquo Physical and Chemical News vol32 pp 81ndash87 2006

[34] L Yang J-K Feng and A-M Ren ldquoTheoretical studies onthe electronic and optical properties of two thiophene-fluorenebased 120587-conjugated copolymersrdquo Polymer vol 46 no 24 pp10970ndash10981 2005

[35] J L Bredas R Silbey D S Boudreaux and R R ChanceldquoChain-length dependence of electronic and electrochemicalproperties of conjugated systems polyacetylene polypheny-lene polythiophene and polypyrrolerdquo Journal of the AmericanChemical Society vol 105 no 22 pp 6555ndash6559 1983

[36] D Fichou G Horowitz B Xu and F Garnier ldquoStoichiometriccontrol of the successive generation of the radical cation anddication of extended 120572-conjugated oligothiophenes a quantita-tive model for doped polythiophenerdquo Synthetic Metals vol 39no 2 pp 243ndash259 1990

[37] D Fichou G Horowitz Y Nishikitani and F Garnier ldquoSemi-conducting conjugated oligomers for molecular electronicsrdquoSynthetic Metals vol 28 no 1-2 pp 723ndash727 1989

[38] V May and O Kuhn Charge and Energy Transfer Dynamics inMolecular Systems Wiley-VCH Berlin Germany 2000

[39] GDennlerMC Scharber andC J Brabec ldquoPolymer-fullerenebulk-heterojunction solar cellsrdquoAdvancedMaterials vol 21 no13 pp 1323ndash1338 2009

[40] JW Chen andY Cao ldquoDevelopment of novel conjugated donorpolymers for high-efficiency bulk-heterojunction photovoltaicdevicesrdquoAccounts of Chemical Research vol 42 no 11 pp 1709ndash1718 2009

12 Journal of Chemistry

[41] Z Cai-Rong L Zi-Jiang C Yu-Hong C Hong-Shan W You-Zhi and Y Li-Hua ldquoDFT and TDDFT study on organic dyesensitizersD5DST andDSS for solar cellsrdquo Journal ofMolecularStructure THEOCHEM vol 899 no 1ndash3 pp 86ndash93 2009

[42] Y He H-Y Chen J Hou and Y Li ldquoIndene-C60bisadduct a

new acceptor for high-performance polymer solar cellsrdquo Journalof the American Chemical Society vol 132 no 4 pp 1377ndash13822010

[43] S Gunes H Neugebauer and N S Sariciftci ldquoConjugatedpolymer-based organic solar cellsrdquo Chemical Reviews vol 107no 4 pp 1324ndash1338 2007

[44] C J Brabec A Cravino D Meissner et al ldquoOrigin of theopen circuit voltage of plastic solar cellsrdquo Advanced FuntionalMaterials vol 11 no 5 pp 374ndash380 2001

[45] M C Scharber D Muhlbacher M Koppe et al ldquoDesign rulesfor donors in bulk-heterojunction solar cellsmdashtowards 10energy-conversion efficiencyrdquo Advanced Materials vol 18 no6 pp 789ndash794 2006

[46] A Gadisa M Svensson M R Andersson and O InganasldquoCorrelation between oxidation potential and open-circuitvoltage of composite solar cells based on blends of polythio-phenesfullerene derivativerdquoApplied Physics Letters vol 84 no9 pp 1609ndash1611 2004

[47] K Kaneto K Yoshino and Y Inuishi ldquoElectrical and opticalproperties of polythiophene prepared by electrochemical poly-merizationrdquo Solid State Communications vol 46 no 5 pp 389ndash391 1983

[48] D Jacquemin J Preat V Wathelet M Fontaine and E APerpete ldquoThioindigo dyes highly accurate visible spectra withTD-DFTrdquo Journal of the American Chemical Society vol 128 no6 pp 2072ndash2083 2006

[49] N Santhanamoorthi K Senthilkumar and P KolandaivelldquoTautomerization and solvent effects on the absorption andemission properties of the Schiff base NN1015840-bis(salicylidene)-p-phenylenediaminemdasha TDDFT studyrdquoMolecular Physics vol108 no 14 pp 1817ndash1827 2010

[50] J Vasudevan R T Stibrany J Bumby et al ldquoAn edge-over-edgeZn(II) bacteriochlorin dimer having an unshifted Q

119910bandThe

importance of 120587-overlaprdquo Journal of the American ChemicalSociety vol 118 no 46 pp 11676ndash11677 1996

[51] H Scheer and H H Inhoffen ldquoHydroporphyrins reactivityspectroscopy and hydroporphyrin analoguesrdquo in The Por-phyrins DDolphin Ed vol 2 pp 45ndash90 Academic Press NewYork NY USA 1978

[52] R H Friend R W Gymer A B Holmes et al ldquoElectrolumi-nescence in conjugated polymersrdquoNature vol 397 no 6715 pp121ndash128 1999

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

2 Journal of Chemistry

S S

RR

S S

RR

S S

RR

44

4

Head-to-tail (HT) Head-to-head (HH)

8TCOC (HT)

8TCOC (HH)8TOC (HT)

8TOC (HH)

8TCOC (TT)

8TOC (TT)

S S

RR

4

Tail-to-tail (TT) Tail-to-tail (TT)

8TOOC

8T

RR

R = COC

R = OC R = COC

R = OC

R = COC

R = OC

R = OOC

R = H

di

120579i

di

120579i

di

120579i

di

120579i

Figure 1 Sketch map of the structures length bond and dihedral angle

optical devices such as surface light-emitting diodes (SLED)and light-emitting diodes (LED) [9] One of the main goalsin the field of electrically conducting polymers is to developa complete understanding of the relationship between thechemical structure of the polymer and its electronic andconduction properties Once such an insight is achieved thedesired electronic properties could be obtained by specificsynthesis following molecular design The conduction prop-erties of an undoped polymer in terms of the band theoryof solids are known to be related to its electronic propertiessuch as the ionization potential (IP) electronic affinity (EA)and band gap (119864gap) [10] The key factor that determinesthe intrinsic properties of the polythiophene variants is theirband structures particularly the positions of the conductionand valence bands and the gap between them Thereforethe 120587-electrons in conducting polymers play a major role indetermining their electrical conductivity and band structure[11] The energy between the valence and conduction band ofa polymer is related to the lowest energy of its monomer unitsand to the bandwidth resulting from the overlap between themonomer orbitals [12] A band gap is defined as the differencebetween the highest occupied molecular orbital (HOMO)and the lowest unoccupiedmolecular orbital (LUMO) energylevels in the polymer [13]

119864gap = 119864LUMO minus 119864HOMO (ev) (1)

So the electrical conductivity is directly related to the HOMOand LUMO energy of the molecule

2 Methods Computational Details

Full geometry optimizations were performed under no con-straints in the framework of the density functional theory(DFT) by means of the B3LYP functional [the Becke3 and

the LeeminusYangminusParr hybrid functional] using the Gaussian09 program [14] The 6-31G(dp) basis set was chosen as acompromise between the quality of the theoretical approachand the high computational cost associated with the highnumber of dimensions to the problem [15 16]

The HOMO LUMO and energy gaps were also deducedfrom the stable structure of the nonsubstituted forms In thispaper the transition energies were calculated at the groundstate geometries using TD-DFTB3LYP calculations and theresultswere comparedwith the available experimental data Anewly designed function the long-range Coulomb-attenua-ting method (CAM-B3LYP) considered long-range interac-tions by comprising 19 of HF and 81 of B88 exchangeat short range and 65 of HF plus 35 of B88 at longrange [17] Furthermore the CAM-B3LYP method has beenapplied and was found to be reasonably capable of predictingthe excitation energies and the absorption spectra of themolecules [18ndash21] Therefore the vertical excitation energyand electronic absorption spectra were simulated using theTD-CAM-B3LYP method in this work The investigatedpolymers 8T 8TCOO and 8TOC (HH HT and TT) and8TCOC (HH HT and TT) are depicted in Figure 1

3 Results and Discussion

31 Geometric Properties For all molecules geometricalparameters were obtained after total optimization by B3LYP6-31G(dp) To investigate the effect of the substituents on thegeometries and electronic properties the optimized struc-tures of several substituted oligomers built on thiophene8TOOC 8TCOC (HH HT and TT) and 8TOC (HH HTand TT) are compared with the unsubstituted one 8T On theother hand to investigate the effects of different regioregulari-ties (HH HT and TT) are compared between them and with

Journal of Chemistry 3

Table 1 Values of interring bond lengths 119889119894(A) of the studied

compounds obtained by B3LYP6-31G(dp) level

Compounds 1198891119889211988931198894119889511988961198897

8T 1445 1441 1440 1440 1440 1441 1445

8TOCHT 1441 1435 1434 1433 1434 1435 1439HH 1445 1434 1438 1432 1438 1434 1445TT 1439 1438 1432 1437 1432 1438 1439

8TCOCHT 1451 1447 1446 1446 1446 1447 1451HH 1449 1456 1446 1454 1446 1454 1448TT 1459 1446 1455 1446 1455 1446 1459

8TOOC 1442 1439 1438 1438 1438 1439 1442

Table 2 Values of dihedral angle 120579119894(∘) of the studied compounds

obtained by B3LYP6-31G(dp) level

Compounds 1205791120579212057931205794120579512057961205797

8T 17996 17996 17996 17996 17996 17996 17996

8TOCHT 180 180 180 180 180 180 180HH 16149 17996 17017 17969 16986 17998 16151TT 180 180 180 180 180 180 180

8TCOCHT 14637 15518 15694 15419 15729 15234 14824HH 16504 12617 17670 13204 17143 13092 16230TT 12247 17057 12790 16860 12790 17060 12247

8TOOC 17585 17714 17593 17873 17992 17962 17997

the 8T and 8TOOC compounds The geometric characteris-tics given as interring distances (119889

119894) and dihedral angle (120579

119894)

are listed in Tables 1 and 2The optimized structures (see Figure 4) of compounds

(8TCOOC and 8TOC with different regioregularities) arecompared with each other and also with 8T and 8TOOCThegeometric characteristics are given as interring distances (119889

119894)

and used to investigate the effect of different regioregularities(HT HH and TT)The theoretical calculations show that thetorsional angles are evaluated to be about asymp180∘ (a quasi-planar conformation) for 8T and 8TOC (HT and TT confor-mations) whereas the other compounds show an antigaucheangle with an average twist angle between 122∘ and 170∘ for8TCOC (HH and TT) and the 8TCOC (HT) shows the valueof torsion angle between the values of 8TCOC (HH and TT)of about 150∘ (see Tables 1 and 2 and Figures 2 and 3)

The properties of the oligomer for 8TOC (HT and TT)can be explained by the effects of the OCH

3donor group

compared with the CH2-OCH

3groupThe electronic doublet

of the methoxy group increases the conjugation whichpromotes better flatness of the system in contrast to theCH2OCH3groupThese results are audited by the intercyclic

study of the values of the bindings This shows that in goingfrom the 8T compound to 8TOOC and 8TOC (HH TT andHT) compounds there is a reduction of the values of theinterring bindings (see Tables 1 and 2 and Figures 2 and 3)These results may be explained by a repulsion of the OOCH

3

(8TOOC) andOCH3(8TOC) groups among them that favors

the flatness of these systems The comparison of the valuesof the bindings of intercyclic 8T compounds with 8TCOC

shows an increase of these values for those systems withantigauche torsion angles and indicates the strong interaction(attraction) of the CH

2OCH3groups among them

32 Electronic Parameters Table 3 lists the theoretical elec-tronic parameters of the studied conjugated compoundsThecalculated electronic parameters (119864gap LUMO and HOMO)of compounds 8T 8TCOC (HH HT and TT) 8TOOC and8TOC (HH HT and TT) exhibit the destabilization of theHOMO and LUMO levels in comparison with those of theunsubstituted one (8T) due to electron-donating substitutiongroups while in the case of 8TOC there is a net stabilizationof the HOMO and LUMO levels However these compoundshave a smaller energy gap (119864gap) than the unsubstituted onewhich is due to the presence of a methoxy group in the 120573position of the thiophene ring The band gap of 8TOC ismuch smaller than that of the other substituted compoundsThis may be attributed to the number of electron-donatingmethoxy side groups and also to the Coulombic interactionbetween the sulfur of thiophene and oxygen atoms [27 28]The theoretical band gaps computed for isolated chains areexpected to be about 02 eV larger than the values computedin the condensed phase [29] When taking into account thisdifference the band gap values obtained are close to theexperimental data for the octamerThe value of the octamerrsquos8T and 8TOC band gap (222 eV and 193 eV resp aftercorrection) is in accordance with that measured experiment-ally for polythiophene 20ndash23 eV [30 31] and that forpoly(441015840-dimethylbithiophene (8TOC (TT))) was estimatedto be 16 eV [23] The octamer seems to be a useful model toobtain a better understanding of the electronic properties ofthe polymeric system

It is important to examine the HOMO and the LUMOenergies for these oligomers because the relative ordering ofthe occupied and virtual orbital provides a reasonable quali-tative indication of excitation properties In general as shownin Figure 5 (LUMOHOMO) theHOMOs of these oligomerspossess a 120587-bonding character within a subunit and a 120587-antibonding character between the consecutive subunits Onthe other hand the LUMOs possess a 120587-antibonding charac-ter within a subunit and a 120587-bonding character between thesubunits The experiment shows that the HOMO and LUMOenergies are obtained from an empirical formula based onthe onset of the oxidation and reduction peaks measured bythe cyclic voltammetry In theory the HOMO and LUMOenergies can be calculated by the DFT calculation [32 33]However it is noticeable that solid-state packing effects arenot included in the DFT calculations which tend to affectthe HOMO and LUMO energy levels in a thin film comparedwith an isolated molecule as considered in the calculationsEven if these calculated energy levels are not accurate it ispossible to use them to obtain the information by comparingsimilar oligomers or polymers The calculated electronicparameters (Gap HOMO and LUMO) of compounds 8T8TOOC 8TOC (HH HT and HT) and 8TCOC (HH HTand HT) are illustrated in Table 3

In the case of compounds 8TOC 8TOOC and 8TCOCit is notable that there is a systematic change of the HOMOand LUMO energies into the backbone substitution raises

4 Journal of Chemistry

1 2 3 4 5 6 71438

1439

1440

1441

1442

1443

1444

1445

1446

Bond number Bond number

8T8TOOC

1 2 3 4 5 6 7

1440

1444

1448

1452

1456

1460

8T8TCOC (HT)

8TCOC (TT)8TCOC (HH)

1 2 3 4 5 6 7

1432

1434

1436

1438

1440

1442

1444

1446

Bond number

8T8TOC (HT)

8TOC (HH)8TOC (TT)

Valu

es o

f len

gth

bond

(Aring)

Valu

es o

f len

gth

bond

(Aring)

Valu

es o

f len

gth

bond

(Aring)

Figure 2 Optimized C-C bond lengths interring of 8T 8TOOC 8TCOC (HH HT and TT) and 8TOC (HH HT and TT) in neutral stateswith the number of bonds studied by B3LY6-31G(dp) level

Table 3 Energy values of 119864LUMO (eV) 119864HOMO (eV) 119864gap (eV) and the open circuit voltage 119881oc (eV) of the studied molecules

Compounds 119864HOMO (eV) 119864LUMO (eV) 119864gap (eV) 119864gap (eV) exp 119881oc (eV)8T minus473 minus231 242 200 [22] 073

8TOOC minus416 minus170 246 016

8TCOC(HT) minus462 minus196 266 062(HH) minus490 minus188 302 090(TT) minus491 minus181 310 091

8TOC(HT) minus387 minus196 191 mdash(HH) minus389 minus182 207 mdash(TT) minus399 minus186 213 16 [23] mdash

PCBM [24 25] minus610 minus370

or lowers the HOMOLUMO energies in agreement withtheir electron donor character However these compoundshave a smaller energy gap (119864gap) than the unsubstituted one(8T) which is due to the presence of different substituents

as described previously [34 35] The band gap of 8TOC(HH TT and HT) is much smaller than that of the othersubstituted compoundsThismay be attributed to the numberof electron-donating methoxy side groups

Journal of Chemistry 5

1 2 3 4 5 6 7

120

130

140

150

160

170

180

190

200

210

Angle number Angle number

8T8TCOC (HT)

8TCOC (HH)8TCOC (TT)

1 2 3 4 5 6 7160

165

170

175

180

185

190

195

200

8T8TOC (HT)

8TOC (HH)8TOC (TT)

Valu

es o

f dih

edra

l ang

le (∘

)

Valu

es o

f dih

edra

l ang

le (∘

)

Figure 3 Optimized dihedral angle of 8T 8TCOC (HH HT and TT) and 8TOC (HH HT and TT) in neutral states with the number ofbonds studied by B3LY6-31G(dp) level

8T 8TOOC

8TCOC (HT) 8TCOC (TT)

8TCOC (HH)

8TOC (HT) 8TOC (HH)

8TOC (TT)

Figure 4 Optimized structures of the studied oligomers

6 Journal of Chemistry

HOMO LUMO

8T

8TOOC

8TOC (HT)

8TOC (TT)

8TOC (HH)

8TCOC (HT)

8TCOC (TT)

8TCOC (HH)

Figure 5 The contour plots of HOMO and LUMO orbitals of the studied compounds

33 Photovoltaic Properties Generally the most efficientpolymer solar cells are based on the bulk heterojunction(BHJ) structure of the blend of 120587-conjugated polymer donorsand fullerene derivative acceptors [7 36ndash40] Here we stud-ied the photovoltaic properties of polyalkyl thiophene with

[66]-phenyl-C61-butyric acidmethyl ester (PCBM) which isthe most widely used acceptor in solar cell devices The cor-responding structure of the photovoltaic devices is schemat-ically depicted in Figure 6 The difference in the HOMOenergy levels of 8T 8TCOC 8TOOC and the LUMO of

Journal of Chemistry 7En

ergy

(eV

)

HOMO

LUMO

minus65

minus60

minus55

minus50

minus45

minus40

minus35

minus30

minus25

minus20

minus15

PCBM

(C60

)

8TO

C (T

T)

8TO

C (H

T)

8TO

C (H

H)

8TCO

C (T

T)

8TCO

C (H

H)

8TCO

C (H

T)

8TO

OC8T

Voc

Egap

Figure 6 Band structure diagram illustrating the HOMO andLUMO energies of the studied compounds relative to the bandstructure of PCBM

PCBM was 073 eV 016 eV and 062 eV respectively butthe value of 8TOC is negative (Table 3) suggesting that thephotoexcited electron transfer from the study compounds toPCBM may be sufficiently efficient to be useful in photo-voltaic devices [24 41 42]

In principle the optimization of polymer-fullerene solarcells is based on fine-tuning the electronic properties andinteractions of the donor and acceptor components so as toabsorb themaximumquantity of light and generate the great-est number of free charges with minimal concomitant loss ofenergy and transport the charges to the electrodes Howeverit is necessary to know the ideal electronic characteristics thateach component should have for the design of the next gen-eration high-efficiency photovoltaic systems The two com-ponents required in these devices for electronic optimizationare a soluble fullerene (generally a C60 derivative) acceptorand a polymeric donor that can be processed in solutionFullerenes are currently considered to be the ideal acceptorsfor organic solar cells for several reasons First they have anenergetically deep-lying LUMO which endows the moleculewith a very high electron affinity relative to the numerouspotential organic donors [25]

It is apparent that the active layer donor-acceptor com-posite governs all aspects of the mechanism with theexception of charge collection which is based on the elec-tronic interface between the active layer composite and therespective electrode Besides the fundamental mechanisticsteps the open circuit voltage (119881oc) is also governed by theenergetic relationship between the donor and the acceptor(Figure 6) rather than the work functions of the cathode andanode as would be expected from a simplistic view of thesediode devices Specifically the energy difference between theHOMO of the donor and the LUMO of the acceptor is foundto be very closely correlated with the 119881oc value [43ndash45]

The maximum open circuit voltage (119881oc) of the BHJ solarcell is related to the difference between the highest occupiedmolecular orbital (HOMO) of the electron donor and theLUMO of the electron acceptor taking into account theenergy lost during the photocharge generation [46] The the-oretical values of open circuit voltage119881oc have been calculatedfrom the following expression

119881oc =10038161003816100381610038161003816119864HOMO

(Donor)10038161003816100381610038161003816minus

10038161003816100381610038161003816119864LUMO

(Acceptor)10038161003816100381610038161003816minus 03 (2)

Moreover these compounds have absorption maxima in theneighborhood of 400ndash540 nm (Table 4) which is the opti-mum range of absorption (UV-visible) for photovoltaic cellsIn addition they have an energy gap of the order of 200 eV(Table 3) for the elevation of the electron from the HOMO tothe LUMO orbitals This characteristic allows us to promotethese compounds for the production of solar cells Thesevalues are sufficient for a possible efficient electron injectionsystem Therefore all the studied molecules can be used asorganic solar cell components because the electron injectionprocess from the excited molecule to the conduction bandof the acceptor (PCBM) and the subsequent regeneration ispossible in photovoltaic cells

4 Optoelectronic Parameters

41 Electronic Absorption Spectra For a better understandingof the electronic properties of thiophene-based moleculesthe excitation energy based on the first and second singlet-singlet electronic transitions has been studied In recentyears time dependent density functional theory (TD-DFT)has emerged as a reliable standard tool for the theoreticaltreatment of electronic excitation spectra and recent worksdemonstrate better accuracy for a wide range of systems [4748] The TD-DFTB3LYP6-31G(dp) has been used on thebasis of the optimized geometry The nature and the energyof the singlet-singlet electronic transitions of all the oligomersin all series under study are reported in Table 4 All electronictransitions are 120587 rarr 120587lowast type and no localized electronictransitions are exhibited among the calculated singlet-singlettransition Table 4 summarizes the transition energies ofabsorption spectra and oscillator strength Two interestingtrends in oscillator strength can be found in all series ofcompounds the oscillator strength OS of 119878

0rarr 1198781is the

overwhelmingly largest of all the series of polymersAccording to Table 4 we note an excitation energy of

about 2 eV for all compounds studied In addition absorp-tion maxima were located in the 400ndash540 nm range for allcompounds indicating all molecules have only one band inthe visible region (120582abs gt 400 nm) The absorption spectra ofthese compounds showed a major absorption band assignedto the 120587 rarr 120587lowast transition local electron

According to the transition character most of the com-pounds show the HOMOrarr LUMO transition as the firstsinglet excitationThemaximum (120582max) wavelengths for UV-vis absorption spectra of all compounds simulated are shownin Figure 7 The calculated 120582max by TD-DFT-B3LY and TD-CAM-B3LYP is different by about 99 nm = 120582max(B3LYP) minus120582max(CAM-B3LYP)

8 Journal of Chemistry

Table 4 Excitation energy valuesΔ119864 for the studied compounds obtained by TD-DFTCAM-B3LYP TD-DFT B3LYPwith 6-31G (dp) level

Compounds 120582 (nm) Exp [26] TD-B3LYP TD-CAM-B3LYP (DMSO) TD-CAM-B3LYP120582 (nm) 119864 (eV) (OS) 120582 (nm) 119864 (eV) (OS) 120582 (nm) 119864 (eV) (OS) Molecular orbital

8T 44864459 192 (29063) 49362 251 (30912) 47807 259 (29578)

Hrarr L (063)55329 224 (0000) 41015 302 (0000) 39233 310 (00000)53639 231 (0000) 32315 383 (0000) 32300 383 (00000)

8TOC

HT71723 172 (14020) 54514 227 (32032) 52971 234 (29449)

Hrarr L (064)55736 222 (16056) 43788 283 (00002) 42071 294 (00021)51485 240 (00072) 36582 338 (02814) 36469 339 (02123)

HH66172 187 (28471) 56823 218 (31391) 54455 227 (30037)

Hrarr L (064)465 55155 224 (0000) 45348 273 (0000) 43004 288 (0000)45297 273 (0000) 36233 342 (0000) 36074 343 (0000)

TT64658 191 (28253) 55533 223 (30750) 53332 232 (29676)

Hrarr L (064)53795 230 (0000) 44230 280 (00041) 42118 294 (00035)

47532 260 (0000) 35593 348(00004) 35462 349 (00001)

8TCOC

HT52952 234 (24562) 45023 275 (25260) 43961 282 (28030)

Hrarr L (062)44536 278 (00966) 38134 325 (00568) 36861 336 (00488)42203 293 (00397) 33152 373 (03015) 32230 384 (02428)

HH47208 262 (21440) 40435 306 (26989) 39618 312 (25865)

Hrarr L (062)mdash 40834 303 (00008) 35682 347 (00998) 34623 358 (00852)

39627 312 (00661) 31908 388 (02093) 28581 433 (00000)

TT46712 265 (20300) 41163 301 (27553) 39282 315 (24701)

Hrarr L (062)40397 306 (00042) 36159 342 (00509) 34187 362 (00641)39818 311 (00434) 32429 382 (03900) 31340 395 (04098)

8TOOC mdash57329 216 (26859) 48934 253 (30704) 47422 261 (29274)

Hrarr L (064)47995 258 (0000) 40835 305 (0000) 39248 315 (00001)44588 278 (0000) 34835 355 (02826) 33704 367 (02340)

The prediction of the excitation energies and oscillatorstrengths by using the CAM-B3LYP is in better agreementwith the experimental results [49 50] than is found forB3LYP because the CAM- (Coulomb-attenuating method-)B3LYP also takes account of the long-range corrections fordescribing the long 120587-conjugation [51]The results are shownin Table 4 and we note that the excitation energy values Δ119864obtained by TD-DFTCAM-B3LYP6-31G(dp) level are inagreement with those obtained by the methods DFTB3LYP6-31G(dp) level therefore theCAM-B3LYP functional is veryuseful for predicting the excitation energies and oscillatorstrengths The values calculated using the TD-DFT CAM-B3LYP function of our compounds in vacuo for predictingthe excitation energies and oscillator strengths are listed inTable 4 The TDCAM-B3LYP6-31G(dp) method was alsoemployed to simulate the optical property of the compounds

42 Effect of Solvent Solvent effects attract considerable atte-ntion because most of the chemical processes occur in thesolution phaseThe solvent effects are included here to ensure

that the calculations are compatible with the typical con-ditions The effects of chemical environment are discussedfurther as follows In order to study the effect of solvents onthe ground state molecular geometry excitation energies andmaximum absorption quantum chemical calculations on thestudied molecules were carried out in vacuum in dimethylsulfoxide (DMSO) The longest wavelength peaks from C-PCM-TD-CAM-B3LYP6-31G(dp) results are shifted com-pared to the corresponding ones using the TD-CAM-B3LYPresults The magnitudes of the spectral shifts are about 15 nmfor 8T 8TOC (HT) and 8TOOC and 1881 2201 2368 817and 1062 nm for 8TCOC (TT) 8TOC (TT) 8TOC (HH)8TCOC (HH) and 8TCOC (HT) respectively The absorp-tionmaxima of all compounds are further shifted by the effectof the dimethyl sulfoxide solventThis might be related to thegradient electrostatic potential and donor effect of the OCH

3

CH2OCH3 and OOCH

3groups Further there is a variation

of the absorption maximum displacement for the samecompound (HT TT andHH) this is the result of the differentconfigurations that one compound can take In DMSO

Journal of Chemistry 9

200 300 400 500 600 700 800 900 1000 1100

0

20000

40000

60000

80000

100000

120000

140000

8TAbEm

200 300 400 500 600 700 800 900 1000 1100

0

20000

40000

60000

80000

100000

120000

140000

8OOCAbEm

120582 (nm) 120582 (nm)

Ener

gy (a

u)

Ener

gy (a

u)

Δ120582

200 300 400 500 600 700 800 900 1000 1100

0

20000

40000

60000

80000

100000

120000

140000

AbsorptionEmission

8TCOCHHabHHemHTab

HTemTTabTTem

300 400 500 600 700 800 900 1000 1100 1200 1300

0

20000

40000

60000

80000

100000

120000Absorption Emission

8TCOHHabHHemHTab

HTemTTabTTem

120582 (nm) 120582 (nm)

Ener

gy (a

u)

Ener

gy (a

u)

Figure 7 Calculated electronic absorption and emission of octamers units of 8T 8TOC (HH HT and TT) 8TOOC and 8TCOC (HH HTand TT) obtained by CAM-B3LYP6-31G(dp)

the calculated results for the absorptionmaximumof all com-pounds are located between 56823 and 40435 nm (Table 4)The peak positions of those molecules in DMSO show a redshift when compared to those measured experimentally [26]

43 Electronic Emission Spectra TD-DFTB3LYP6-31G(dp)has been used for optimized structures and CAM-B3LYP6-31G(dp) was used to calculate the excited state and to sim-ulate the emission spectra of the considered polymers andthe first singlet excited states are listed in Table 5 Similar tothe absorption spectra 119878

1rarr 1198780fluorescence peaks in emi-

ssion spectra (Figure 6) have the greatest oscillator strengthsin all molecules and exclusively arise fromHOMOrarr LUMO(120587 rarr 120587lowast electronic transition) Polymers with aromatic orheterocyclic units generally absorb light with wavelengths in

the range from 300 to 700 nm due to 120587 rarr 120587lowast transitionsThe excited states of their chromophores (excitons) releaseenergy radiatively as well as nonradiatively on returning tothe ground state [26] The radiative decay of excitons to theground state can emit visible light These excitons are alsoformed when a bias potential is applied to an emissive poly-mer sandwiched between an anode and a cathode [52]

The theoretical studies of our molecules can be used toderive the Stokes shifts the difference between the positionof the maxima band of the absorption and emission spectrain wavelength which is about 80 to 93 nm for the structures8T 8TOC (HH TT and HT) 8TCOC (TT) and 8TOOCbut that for the 8TCOC (HH) and 8TCOC (TT) is 149 nmAmong them the compound 8TCOC has a relatively largerStokes shift which indicates that electron transitions break

10 Journal of Chemistry

Table 5 Emission spectra in gaseous phase obtained by the TD-CAM-B3LYP6-31G(d) optimized geometries of 119878

1excited states for

the octamers

Compounds 120582 (nm) 119864 (eV) OS Δ120582 = 120582ab minus 120582em55797 222 30531

8T 43390 285 00000 79836564 339 00000

8TOC

HT62147 199 29482

817646113 268 0005742181 293 02710

HH63709 196 30801

925446191 268 0000040654 304 00000

TT62147 199 29482

881546113 268 0005742181 293 02710

8TCOC

TT53079 233 26028

911840043 309 0035434914 355 03253

HH54518 247 27840

1490040748 304 0027535560 348 00001

HT56951 217 30310

1766942626 290 0000136784 337 0007956106 220 29875

8TOOC 42641 290 00002 868436421 340 00000

the strong conjugate effect leading to remarkable changes inthe structure and reorganization energy as discussed above

5 Conclusions

In this study we have used the DFTB3LYP method to inves-tigate the theoretical analysis of the geometries and electronicproperties of some type-in-derivatives structure of polythio-phene The modification of chemical structures can greatlymodify and improve the electronic and optical properties ofpristine studied materials The electronic properties of theconjugated materials based on thiophene compounds havebeen computed using the 6-31G(dp) basis set at a densityfunctional B3LYP level in order to guide the synthesis ofnovel materials with specific electronic properties

In summary the conclusions are as follows

(i) TheUV-vis absorption properties have been obtainedby using TDCAM-B3LYP and TD-B3LYP calcula-tions The obtained absorption maximums are in therange of 350ndash550 nm

(ii) The HOMO level LUMO level and band gap ofthe studied compounds were well controlled by theacceptor strength The calculated band gap (119864gap) ofthe studiedmolecules was in the range of 191ndash302 eV

(iii) The calculated values of 119881oc of the studied moleculesrange from 016 eV to 091 eVPCBM these values aresufficient for a possible efficient electron injection

The theoretical results suggest that both the donor strengthand the stable geometry contribute significantly to the elec-tronic properties of the conjugated polymers Finally the pro-cedures of theoretical calculations can be employed to predictthe electronic properties of the other compounds and furtherto design novel materials for organic solar cells

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work has been supported by the Volubilis Program(no MA11248) and the convention CNRSTCNRS (ProjectChimie 1009) The authors are grateful to the ldquoAssociationMarocaine des Chimistes Theoriciensrdquo (AMCT) for its per-tinent help Guillermo Salgado-Moran gratefully acknowl-edges Si Mohamed Bouzzine for his invitation to participatein this work Daniel Glossman-Mitnik is a researcher ofCIMAV and CONACYT and acknowledges both institutionsfor partial support

References

[1] H-J Wang C-P Chen and R-J Jeng ldquoPolythiophenes com-prising conjugated pendants for polymer solar cells a reviewrdquoMaterials vol 7 no 4 pp 2411ndash2439 2014

[2] S Pesant P Boulanger M Cote and M Ernzerhof ldquoAb initiostudy of ladder-type polymers polythiophene and polypyrrolerdquoChemical Physics Letters vol 450 no 4ndash6 pp 329ndash334 2008

[3] J Roncali ldquoConjugated poly(thiophenes) synthesis functional-ization and applicationsrdquo Chemical Reviews vol 92 no 4 pp711ndash738 1992

[4] Y Wei C-C Chan J Tian G-W Jang and K F HsuehldquoElectrochemical polymerization of thiophenes in the presenceof bithiophene or terthiophene kinetics and mechanism of thepolymerizationrdquo Chemistry of Materials vol 3 no 5 pp 888ndash897 1991

[5] R M Souto Maior K Hinkelmann H Eckert and FWudl ldquoSynthesis and characterization of two regiochemi-cally defined poly(dialkylbithiophenes) a comparative studyrdquoMacromolecules vol 23 no 5 pp 1268ndash1279 1990

[6] M-A Sato and H Morii ldquoNuclear magnetic resonance stud-ies on electrochemically prepared poly(3-dodecylthiophene)rdquoMacromolecules vol 24 no 5 pp 1196ndash1200 1991

[7] Y-J Cheng S-H Yang and C-S Hsu ldquoSynthesis of conjugatedpolymers for organic solar cell applicationsrdquo Chemical Reviewsvol 109 no 11 pp 5868ndash5923 2009

[8] A C AlgunoW C Chung R V Bantaculo et al ldquoAb initio anddensity functional studies of polythiophene energy band gaprdquoNECTEC Technical Journal vol 2 no 9 pp 215ndash218 2001

[9] J Pei W-L Yu W Huang and A J Heeger ldquoA novel series ofefficient thiophene-based light-emitting conjugated polymersand application in polymer light-emitting diodesrdquo Macro-molecules vol 33 no 7 pp 2462ndash2471 2000

Journal of Chemistry 11

[10] A K Bakhshi ldquoTheoretical tailoring of electrically conductingpolymers some new resultsrdquoMaterials Science and EngineeringC vol 3 no 3-4 pp 249ndash255 1995

[11] M S Senevirathne A Nanayakkara and G K R Senadeera ldquoAtheoretical investigation of band gaps of conducting polymersmdashpolythiophene polypyrrole and polyfuranrdquo inProceedings of the23rd Technical Sessions vol 23 pp 47ndash53 Institute of PhysicsColombo Sri Lanka March 2007

[12] U Salzner J B Lagowski P G Pickup and R A PoirierldquoDesign of low band gap polymers employing density func-tional theorymdashhybrid functionals ameliorate band gap prob-lemrdquo Journal of Computational Chemistry vol 18 no 15 pp1943ndash1953 1997

[13] E Bundgaard and F C Krebs ldquoLow band gap polymers fororganic photovoltaicsrdquo Solar Energy Materials and Solar Cellsvol 91 no 11 pp 954ndash985 2007

[14] M J Frisch G W Trucks H B Schlegel et al ldquoGaussian 09Revision B04rdquo Gaussian Inc Wallingford Conn USA 2009

[15] M E Casida C Jamorski K C Casida and D R SalahubldquoMolecular excitation energies to high-lying bound states fromtime-dependent density-functional response theory charac-terization and correction of the time-dependent local den-sity approximation ionization thresholdrdquo Journal of ChemicalPhysics vol 108 no 11 pp 4439ndash4449 1998

[16] R E Stratmann G E Scuseria and M J Frisch ldquoAn efficientimplementation of time-dependent density-functional theoryfor the calculation of excitation energies of largemoleculesrdquoTheJournal of Chemical Physics vol 109 no 19 pp 8218ndash8224 1998

[17] T Yanai D P Tew and N C Handy ldquoA new hybrid exchange-correlation functional using the Coulomb-attenuating method(CAM-B3LYP)rdquo Chemical Physics Letters vol 393 no 1ndash3 pp51ndash57 2004

[18] J Preat ldquoPhotoinduced energy-transfer and electron-transferprocesses in dye-sensitized solar cells TDDFT insights fortriphenylamine dyesrdquoThe Journal of Physical Chemistry C vol114 no 39 pp 16716ndash16725 2010

[19] B Camino M de La Pierre and A M Ferrari ldquoPhotoelectro-chemical properties of the CT1 dye a DFT studyrdquo Journal ofMolecular Structure vol 1046 pp 116ndash123 2013

[20] A Irfan R Jin A G Al-Sehemi and A M Asiri ldquoQuantumchemical study of the donor-bridge-acceptor triphenylaminebased sensitizersrdquo Spectrochimica Acta Part A Molecular andBiomolecular Spectroscopy vol 110 pp 60ndash66 2013

[21] S Jungsuttiwong R Tarsang T Sudyoadsuk V Promarak PKhongpracha and S Namuangruk ldquoTheoretical study on noveldouble donor-based dyes used in high efficient dye-sensitizedsolar cells the application of TDDFT study to the electroninjection processrdquoOrganic Electronics PhysicsMaterials Appli-cations vol 14 no 3 pp 711ndash722 2013

[22] E J Meijer D M de Leeuw S Setayesh et al ldquoSolution-processed ambipolar organic field-effect transistors and invert-ersrdquo Nature Materials vol 2 no 10 pp 678ndash682 2003

[23] V Hernandez J T L Navarrete and J L Marcos ldquoElectronicstructure and lattice dynamics of polyfuranrdquo Synthetic Metalsvol 41 no 3 pp 789ndash792 1991

[24] F B Kooistra J Knol F Kastenberg et al ldquoIncreasing the opencircuit voltage of bulk-heterojunction solar cells by raising theLUMO level of the acceptorrdquo Organic Letters vol 9 no 4 pp551ndash554 2007

[25] J J M Halls J Cornil D A dos Santos et al ldquoCharge- andenergy-transfer processes at polymerpolymer interfaces a joint

experimental and theoretical studyrdquo Physical Review B vol 60no 8 pp 5721ndash5727 1999

[26] M Fall J-J Aaron and D Gningue-Sall ldquoLuminescence prop-erties of poly(3-methoxythiophene)mdashbithiophene compositeoligomersrdquo Journal of Fluorescence vol 10 no 2 pp 107ndash1112000

[27] M Cossi N Rega G Scalmani and V Barone ldquoEnergiesstructures and electronic properties of molecules in solutionwith the C-PCM solvation modelrdquo Journal of ComputationalChemistry vol 24 no 6 pp 669ndash681 2003

[28] V Barone and M Cossi ldquoQuantum calculation of molecularenergies and energy gradients in solution by a conductor solventmodelrdquoThe Journal of Physical Chemistry A vol 102 no 11 pp1995ndash2001 1998

[29] J F Pan S J Chua and W Huang ldquoQuantum calculationof molecular energies and energy gradients in solution by aconductor solventmodelrdquoChemical Physics Letters vol 363 no1-2 pp 18ndash24 2002

[30] U Salzner J B Lagowski P G Pickup and R A Poirier ldquoCom-parison of geometries and electronic structures of polyacety-lene polyborole polycyclopentadiene polypyrrole polyfuranpolysilole polyphosphole polythiophene polyselenophene andpolytellurophenerdquo Synthetic Metals vol 96 no 3 pp 177ndash1891998

[31] A Kraak and H Wynberg ldquoCharge-transfer interaction ofdithienyls and cyclopentadithiophenes with 135-trinitroben-zene (TNB)rdquo Tetrahedron vol 24 no 10 pp 3881ndash3885 1968

[32] M Dietrich and J Heinze ldquoPoly(441015840-dimethoxybithiophe-ne)mdasha new conducting polymer with extraordinary redox andoptical propertiesrdquo SyntheticMetals vol 41 no 1-2 pp 503ndash5061991

[33] H Zgou M Hamidi M Bouachrine and K Hasnaoui ldquoTheDFT study and opto-electronic properties of copolymers basedon thiophene and phenylenerdquo Physical and Chemical News vol32 pp 81ndash87 2006

[34] L Yang J-K Feng and A-M Ren ldquoTheoretical studies onthe electronic and optical properties of two thiophene-fluorenebased 120587-conjugated copolymersrdquo Polymer vol 46 no 24 pp10970ndash10981 2005

[35] J L Bredas R Silbey D S Boudreaux and R R ChanceldquoChain-length dependence of electronic and electrochemicalproperties of conjugated systems polyacetylene polypheny-lene polythiophene and polypyrrolerdquo Journal of the AmericanChemical Society vol 105 no 22 pp 6555ndash6559 1983

[36] D Fichou G Horowitz B Xu and F Garnier ldquoStoichiometriccontrol of the successive generation of the radical cation anddication of extended 120572-conjugated oligothiophenes a quantita-tive model for doped polythiophenerdquo Synthetic Metals vol 39no 2 pp 243ndash259 1990

[37] D Fichou G Horowitz Y Nishikitani and F Garnier ldquoSemi-conducting conjugated oligomers for molecular electronicsrdquoSynthetic Metals vol 28 no 1-2 pp 723ndash727 1989

[38] V May and O Kuhn Charge and Energy Transfer Dynamics inMolecular Systems Wiley-VCH Berlin Germany 2000

[39] GDennlerMC Scharber andC J Brabec ldquoPolymer-fullerenebulk-heterojunction solar cellsrdquoAdvancedMaterials vol 21 no13 pp 1323ndash1338 2009

[40] JW Chen andY Cao ldquoDevelopment of novel conjugated donorpolymers for high-efficiency bulk-heterojunction photovoltaicdevicesrdquoAccounts of Chemical Research vol 42 no 11 pp 1709ndash1718 2009

12 Journal of Chemistry

[41] Z Cai-Rong L Zi-Jiang C Yu-Hong C Hong-Shan W You-Zhi and Y Li-Hua ldquoDFT and TDDFT study on organic dyesensitizersD5DST andDSS for solar cellsrdquo Journal ofMolecularStructure THEOCHEM vol 899 no 1ndash3 pp 86ndash93 2009

[42] Y He H-Y Chen J Hou and Y Li ldquoIndene-C60bisadduct a

new acceptor for high-performance polymer solar cellsrdquo Journalof the American Chemical Society vol 132 no 4 pp 1377ndash13822010

[43] S Gunes H Neugebauer and N S Sariciftci ldquoConjugatedpolymer-based organic solar cellsrdquo Chemical Reviews vol 107no 4 pp 1324ndash1338 2007

[44] C J Brabec A Cravino D Meissner et al ldquoOrigin of theopen circuit voltage of plastic solar cellsrdquo Advanced FuntionalMaterials vol 11 no 5 pp 374ndash380 2001

[45] M C Scharber D Muhlbacher M Koppe et al ldquoDesign rulesfor donors in bulk-heterojunction solar cellsmdashtowards 10energy-conversion efficiencyrdquo Advanced Materials vol 18 no6 pp 789ndash794 2006

[46] A Gadisa M Svensson M R Andersson and O InganasldquoCorrelation between oxidation potential and open-circuitvoltage of composite solar cells based on blends of polythio-phenesfullerene derivativerdquoApplied Physics Letters vol 84 no9 pp 1609ndash1611 2004

[47] K Kaneto K Yoshino and Y Inuishi ldquoElectrical and opticalproperties of polythiophene prepared by electrochemical poly-merizationrdquo Solid State Communications vol 46 no 5 pp 389ndash391 1983

[48] D Jacquemin J Preat V Wathelet M Fontaine and E APerpete ldquoThioindigo dyes highly accurate visible spectra withTD-DFTrdquo Journal of the American Chemical Society vol 128 no6 pp 2072ndash2083 2006

[49] N Santhanamoorthi K Senthilkumar and P KolandaivelldquoTautomerization and solvent effects on the absorption andemission properties of the Schiff base NN1015840-bis(salicylidene)-p-phenylenediaminemdasha TDDFT studyrdquoMolecular Physics vol108 no 14 pp 1817ndash1827 2010

[50] J Vasudevan R T Stibrany J Bumby et al ldquoAn edge-over-edgeZn(II) bacteriochlorin dimer having an unshifted Q

119910bandThe

importance of 120587-overlaprdquo Journal of the American ChemicalSociety vol 118 no 46 pp 11676ndash11677 1996

[51] H Scheer and H H Inhoffen ldquoHydroporphyrins reactivityspectroscopy and hydroporphyrin analoguesrdquo in The Por-phyrins DDolphin Ed vol 2 pp 45ndash90 Academic Press NewYork NY USA 1978

[52] R H Friend R W Gymer A B Holmes et al ldquoElectrolumi-nescence in conjugated polymersrdquoNature vol 397 no 6715 pp121ndash128 1999

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

Journal of Chemistry 3

Table 1 Values of interring bond lengths 119889119894(A) of the studied

compounds obtained by B3LYP6-31G(dp) level

Compounds 1198891119889211988931198894119889511988961198897

8T 1445 1441 1440 1440 1440 1441 1445

8TOCHT 1441 1435 1434 1433 1434 1435 1439HH 1445 1434 1438 1432 1438 1434 1445TT 1439 1438 1432 1437 1432 1438 1439

8TCOCHT 1451 1447 1446 1446 1446 1447 1451HH 1449 1456 1446 1454 1446 1454 1448TT 1459 1446 1455 1446 1455 1446 1459

8TOOC 1442 1439 1438 1438 1438 1439 1442

Table 2 Values of dihedral angle 120579119894(∘) of the studied compounds

obtained by B3LYP6-31G(dp) level

Compounds 1205791120579212057931205794120579512057961205797

8T 17996 17996 17996 17996 17996 17996 17996

8TOCHT 180 180 180 180 180 180 180HH 16149 17996 17017 17969 16986 17998 16151TT 180 180 180 180 180 180 180

8TCOCHT 14637 15518 15694 15419 15729 15234 14824HH 16504 12617 17670 13204 17143 13092 16230TT 12247 17057 12790 16860 12790 17060 12247

8TOOC 17585 17714 17593 17873 17992 17962 17997

the 8T and 8TOOC compounds The geometric characteris-tics given as interring distances (119889

119894) and dihedral angle (120579

119894)

are listed in Tables 1 and 2The optimized structures (see Figure 4) of compounds

(8TCOOC and 8TOC with different regioregularities) arecompared with each other and also with 8T and 8TOOCThegeometric characteristics are given as interring distances (119889

119894)

and used to investigate the effect of different regioregularities(HT HH and TT)The theoretical calculations show that thetorsional angles are evaluated to be about asymp180∘ (a quasi-planar conformation) for 8T and 8TOC (HT and TT confor-mations) whereas the other compounds show an antigaucheangle with an average twist angle between 122∘ and 170∘ for8TCOC (HH and TT) and the 8TCOC (HT) shows the valueof torsion angle between the values of 8TCOC (HH and TT)of about 150∘ (see Tables 1 and 2 and Figures 2 and 3)

The properties of the oligomer for 8TOC (HT and TT)can be explained by the effects of the OCH

3donor group

compared with the CH2-OCH

3groupThe electronic doublet

of the methoxy group increases the conjugation whichpromotes better flatness of the system in contrast to theCH2OCH3groupThese results are audited by the intercyclic

study of the values of the bindings This shows that in goingfrom the 8T compound to 8TOOC and 8TOC (HH TT andHT) compounds there is a reduction of the values of theinterring bindings (see Tables 1 and 2 and Figures 2 and 3)These results may be explained by a repulsion of the OOCH

3

(8TOOC) andOCH3(8TOC) groups among them that favors

the flatness of these systems The comparison of the valuesof the bindings of intercyclic 8T compounds with 8TCOC

shows an increase of these values for those systems withantigauche torsion angles and indicates the strong interaction(attraction) of the CH

2OCH3groups among them

32 Electronic Parameters Table 3 lists the theoretical elec-tronic parameters of the studied conjugated compoundsThecalculated electronic parameters (119864gap LUMO and HOMO)of compounds 8T 8TCOC (HH HT and TT) 8TOOC and8TOC (HH HT and TT) exhibit the destabilization of theHOMO and LUMO levels in comparison with those of theunsubstituted one (8T) due to electron-donating substitutiongroups while in the case of 8TOC there is a net stabilizationof the HOMO and LUMO levels However these compoundshave a smaller energy gap (119864gap) than the unsubstituted onewhich is due to the presence of a methoxy group in the 120573position of the thiophene ring The band gap of 8TOC ismuch smaller than that of the other substituted compoundsThis may be attributed to the number of electron-donatingmethoxy side groups and also to the Coulombic interactionbetween the sulfur of thiophene and oxygen atoms [27 28]The theoretical band gaps computed for isolated chains areexpected to be about 02 eV larger than the values computedin the condensed phase [29] When taking into account thisdifference the band gap values obtained are close to theexperimental data for the octamerThe value of the octamerrsquos8T and 8TOC band gap (222 eV and 193 eV resp aftercorrection) is in accordance with that measured experiment-ally for polythiophene 20ndash23 eV [30 31] and that forpoly(441015840-dimethylbithiophene (8TOC (TT))) was estimatedto be 16 eV [23] The octamer seems to be a useful model toobtain a better understanding of the electronic properties ofthe polymeric system

It is important to examine the HOMO and the LUMOenergies for these oligomers because the relative ordering ofthe occupied and virtual orbital provides a reasonable quali-tative indication of excitation properties In general as shownin Figure 5 (LUMOHOMO) theHOMOs of these oligomerspossess a 120587-bonding character within a subunit and a 120587-antibonding character between the consecutive subunits Onthe other hand the LUMOs possess a 120587-antibonding charac-ter within a subunit and a 120587-bonding character between thesubunits The experiment shows that the HOMO and LUMOenergies are obtained from an empirical formula based onthe onset of the oxidation and reduction peaks measured bythe cyclic voltammetry In theory the HOMO and LUMOenergies can be calculated by the DFT calculation [32 33]However it is noticeable that solid-state packing effects arenot included in the DFT calculations which tend to affectthe HOMO and LUMO energy levels in a thin film comparedwith an isolated molecule as considered in the calculationsEven if these calculated energy levels are not accurate it ispossible to use them to obtain the information by comparingsimilar oligomers or polymers The calculated electronicparameters (Gap HOMO and LUMO) of compounds 8T8TOOC 8TOC (HH HT and HT) and 8TCOC (HH HTand HT) are illustrated in Table 3

In the case of compounds 8TOC 8TOOC and 8TCOCit is notable that there is a systematic change of the HOMOand LUMO energies into the backbone substitution raises

4 Journal of Chemistry

1 2 3 4 5 6 71438

1439

1440

1441

1442

1443

1444

1445

1446

Bond number Bond number

8T8TOOC

1 2 3 4 5 6 7

1440

1444

1448

1452

1456

1460

8T8TCOC (HT)

8TCOC (TT)8TCOC (HH)

1 2 3 4 5 6 7

1432

1434

1436

1438

1440

1442

1444

1446

Bond number

8T8TOC (HT)

8TOC (HH)8TOC (TT)

Valu

es o

f len

gth

bond

(Aring)

Valu

es o

f len

gth

bond

(Aring)

Valu

es o

f len

gth

bond

(Aring)

Figure 2 Optimized C-C bond lengths interring of 8T 8TOOC 8TCOC (HH HT and TT) and 8TOC (HH HT and TT) in neutral stateswith the number of bonds studied by B3LY6-31G(dp) level

Table 3 Energy values of 119864LUMO (eV) 119864HOMO (eV) 119864gap (eV) and the open circuit voltage 119881oc (eV) of the studied molecules

Compounds 119864HOMO (eV) 119864LUMO (eV) 119864gap (eV) 119864gap (eV) exp 119881oc (eV)8T minus473 minus231 242 200 [22] 073

8TOOC minus416 minus170 246 016

8TCOC(HT) minus462 minus196 266 062(HH) minus490 minus188 302 090(TT) minus491 minus181 310 091

8TOC(HT) minus387 minus196 191 mdash(HH) minus389 minus182 207 mdash(TT) minus399 minus186 213 16 [23] mdash

PCBM [24 25] minus610 minus370

or lowers the HOMOLUMO energies in agreement withtheir electron donor character However these compoundshave a smaller energy gap (119864gap) than the unsubstituted one(8T) which is due to the presence of different substituents

as described previously [34 35] The band gap of 8TOC(HH TT and HT) is much smaller than that of the othersubstituted compoundsThismay be attributed to the numberof electron-donating methoxy side groups

Journal of Chemistry 5

1 2 3 4 5 6 7

120

130

140

150

160

170

180

190

200

210

Angle number Angle number

8T8TCOC (HT)

8TCOC (HH)8TCOC (TT)

1 2 3 4 5 6 7160

165

170

175

180

185

190

195

200

8T8TOC (HT)

8TOC (HH)8TOC (TT)

Valu

es o

f dih

edra

l ang

le (∘

)

Valu

es o

f dih

edra

l ang

le (∘

)

Figure 3 Optimized dihedral angle of 8T 8TCOC (HH HT and TT) and 8TOC (HH HT and TT) in neutral states with the number ofbonds studied by B3LY6-31G(dp) level

8T 8TOOC

8TCOC (HT) 8TCOC (TT)

8TCOC (HH)

8TOC (HT) 8TOC (HH)

8TOC (TT)

Figure 4 Optimized structures of the studied oligomers

6 Journal of Chemistry

HOMO LUMO

8T

8TOOC

8TOC (HT)

8TOC (TT)

8TOC (HH)

8TCOC (HT)

8TCOC (TT)

8TCOC (HH)

Figure 5 The contour plots of HOMO and LUMO orbitals of the studied compounds

33 Photovoltaic Properties Generally the most efficientpolymer solar cells are based on the bulk heterojunction(BHJ) structure of the blend of 120587-conjugated polymer donorsand fullerene derivative acceptors [7 36ndash40] Here we stud-ied the photovoltaic properties of polyalkyl thiophene with

[66]-phenyl-C61-butyric acidmethyl ester (PCBM) which isthe most widely used acceptor in solar cell devices The cor-responding structure of the photovoltaic devices is schemat-ically depicted in Figure 6 The difference in the HOMOenergy levels of 8T 8TCOC 8TOOC and the LUMO of

Journal of Chemistry 7En

ergy

(eV

)

HOMO

LUMO

minus65

minus60

minus55

minus50

minus45

minus40

minus35

minus30

minus25

minus20

minus15

PCBM

(C60

)

8TO

C (T

T)

8TO

C (H

T)

8TO

C (H

H)

8TCO

C (T

T)

8TCO

C (H

H)

8TCO

C (H

T)

8TO

OC8T

Voc

Egap

Figure 6 Band structure diagram illustrating the HOMO andLUMO energies of the studied compounds relative to the bandstructure of PCBM

PCBM was 073 eV 016 eV and 062 eV respectively butthe value of 8TOC is negative (Table 3) suggesting that thephotoexcited electron transfer from the study compounds toPCBM may be sufficiently efficient to be useful in photo-voltaic devices [24 41 42]

In principle the optimization of polymer-fullerene solarcells is based on fine-tuning the electronic properties andinteractions of the donor and acceptor components so as toabsorb themaximumquantity of light and generate the great-est number of free charges with minimal concomitant loss ofenergy and transport the charges to the electrodes Howeverit is necessary to know the ideal electronic characteristics thateach component should have for the design of the next gen-eration high-efficiency photovoltaic systems The two com-ponents required in these devices for electronic optimizationare a soluble fullerene (generally a C60 derivative) acceptorand a polymeric donor that can be processed in solutionFullerenes are currently considered to be the ideal acceptorsfor organic solar cells for several reasons First they have anenergetically deep-lying LUMO which endows the moleculewith a very high electron affinity relative to the numerouspotential organic donors [25]

It is apparent that the active layer donor-acceptor com-posite governs all aspects of the mechanism with theexception of charge collection which is based on the elec-tronic interface between the active layer composite and therespective electrode Besides the fundamental mechanisticsteps the open circuit voltage (119881oc) is also governed by theenergetic relationship between the donor and the acceptor(Figure 6) rather than the work functions of the cathode andanode as would be expected from a simplistic view of thesediode devices Specifically the energy difference between theHOMO of the donor and the LUMO of the acceptor is foundto be very closely correlated with the 119881oc value [43ndash45]

The maximum open circuit voltage (119881oc) of the BHJ solarcell is related to the difference between the highest occupiedmolecular orbital (HOMO) of the electron donor and theLUMO of the electron acceptor taking into account theenergy lost during the photocharge generation [46] The the-oretical values of open circuit voltage119881oc have been calculatedfrom the following expression

119881oc =10038161003816100381610038161003816119864HOMO

(Donor)10038161003816100381610038161003816minus

10038161003816100381610038161003816119864LUMO

(Acceptor)10038161003816100381610038161003816minus 03 (2)

Moreover these compounds have absorption maxima in theneighborhood of 400ndash540 nm (Table 4) which is the opti-mum range of absorption (UV-visible) for photovoltaic cellsIn addition they have an energy gap of the order of 200 eV(Table 3) for the elevation of the electron from the HOMO tothe LUMO orbitals This characteristic allows us to promotethese compounds for the production of solar cells Thesevalues are sufficient for a possible efficient electron injectionsystem Therefore all the studied molecules can be used asorganic solar cell components because the electron injectionprocess from the excited molecule to the conduction bandof the acceptor (PCBM) and the subsequent regeneration ispossible in photovoltaic cells

4 Optoelectronic Parameters

41 Electronic Absorption Spectra For a better understandingof the electronic properties of thiophene-based moleculesthe excitation energy based on the first and second singlet-singlet electronic transitions has been studied In recentyears time dependent density functional theory (TD-DFT)has emerged as a reliable standard tool for the theoreticaltreatment of electronic excitation spectra and recent worksdemonstrate better accuracy for a wide range of systems [4748] The TD-DFTB3LYP6-31G(dp) has been used on thebasis of the optimized geometry The nature and the energyof the singlet-singlet electronic transitions of all the oligomersin all series under study are reported in Table 4 All electronictransitions are 120587 rarr 120587lowast type and no localized electronictransitions are exhibited among the calculated singlet-singlettransition Table 4 summarizes the transition energies ofabsorption spectra and oscillator strength Two interestingtrends in oscillator strength can be found in all series ofcompounds the oscillator strength OS of 119878

0rarr 1198781is the

overwhelmingly largest of all the series of polymersAccording to Table 4 we note an excitation energy of

about 2 eV for all compounds studied In addition absorp-tion maxima were located in the 400ndash540 nm range for allcompounds indicating all molecules have only one band inthe visible region (120582abs gt 400 nm) The absorption spectra ofthese compounds showed a major absorption band assignedto the 120587 rarr 120587lowast transition local electron

According to the transition character most of the com-pounds show the HOMOrarr LUMO transition as the firstsinglet excitationThemaximum (120582max) wavelengths for UV-vis absorption spectra of all compounds simulated are shownin Figure 7 The calculated 120582max by TD-DFT-B3LY and TD-CAM-B3LYP is different by about 99 nm = 120582max(B3LYP) minus120582max(CAM-B3LYP)

8 Journal of Chemistry

Table 4 Excitation energy valuesΔ119864 for the studied compounds obtained by TD-DFTCAM-B3LYP TD-DFT B3LYPwith 6-31G (dp) level

Compounds 120582 (nm) Exp [26] TD-B3LYP TD-CAM-B3LYP (DMSO) TD-CAM-B3LYP120582 (nm) 119864 (eV) (OS) 120582 (nm) 119864 (eV) (OS) 120582 (nm) 119864 (eV) (OS) Molecular orbital

8T 44864459 192 (29063) 49362 251 (30912) 47807 259 (29578)

Hrarr L (063)55329 224 (0000) 41015 302 (0000) 39233 310 (00000)53639 231 (0000) 32315 383 (0000) 32300 383 (00000)

8TOC

HT71723 172 (14020) 54514 227 (32032) 52971 234 (29449)

Hrarr L (064)55736 222 (16056) 43788 283 (00002) 42071 294 (00021)51485 240 (00072) 36582 338 (02814) 36469 339 (02123)

HH66172 187 (28471) 56823 218 (31391) 54455 227 (30037)

Hrarr L (064)465 55155 224 (0000) 45348 273 (0000) 43004 288 (0000)45297 273 (0000) 36233 342 (0000) 36074 343 (0000)

TT64658 191 (28253) 55533 223 (30750) 53332 232 (29676)

Hrarr L (064)53795 230 (0000) 44230 280 (00041) 42118 294 (00035)

47532 260 (0000) 35593 348(00004) 35462 349 (00001)

8TCOC

HT52952 234 (24562) 45023 275 (25260) 43961 282 (28030)

Hrarr L (062)44536 278 (00966) 38134 325 (00568) 36861 336 (00488)42203 293 (00397) 33152 373 (03015) 32230 384 (02428)

HH47208 262 (21440) 40435 306 (26989) 39618 312 (25865)

Hrarr L (062)mdash 40834 303 (00008) 35682 347 (00998) 34623 358 (00852)

39627 312 (00661) 31908 388 (02093) 28581 433 (00000)

TT46712 265 (20300) 41163 301 (27553) 39282 315 (24701)

Hrarr L (062)40397 306 (00042) 36159 342 (00509) 34187 362 (00641)39818 311 (00434) 32429 382 (03900) 31340 395 (04098)

8TOOC mdash57329 216 (26859) 48934 253 (30704) 47422 261 (29274)

Hrarr L (064)47995 258 (0000) 40835 305 (0000) 39248 315 (00001)44588 278 (0000) 34835 355 (02826) 33704 367 (02340)

The prediction of the excitation energies and oscillatorstrengths by using the CAM-B3LYP is in better agreementwith the experimental results [49 50] than is found forB3LYP because the CAM- (Coulomb-attenuating method-)B3LYP also takes account of the long-range corrections fordescribing the long 120587-conjugation [51]The results are shownin Table 4 and we note that the excitation energy values Δ119864obtained by TD-DFTCAM-B3LYP6-31G(dp) level are inagreement with those obtained by the methods DFTB3LYP6-31G(dp) level therefore theCAM-B3LYP functional is veryuseful for predicting the excitation energies and oscillatorstrengths The values calculated using the TD-DFT CAM-B3LYP function of our compounds in vacuo for predictingthe excitation energies and oscillator strengths are listed inTable 4 The TDCAM-B3LYP6-31G(dp) method was alsoemployed to simulate the optical property of the compounds

42 Effect of Solvent Solvent effects attract considerable atte-ntion because most of the chemical processes occur in thesolution phaseThe solvent effects are included here to ensure

that the calculations are compatible with the typical con-ditions The effects of chemical environment are discussedfurther as follows In order to study the effect of solvents onthe ground state molecular geometry excitation energies andmaximum absorption quantum chemical calculations on thestudied molecules were carried out in vacuum in dimethylsulfoxide (DMSO) The longest wavelength peaks from C-PCM-TD-CAM-B3LYP6-31G(dp) results are shifted com-pared to the corresponding ones using the TD-CAM-B3LYPresults The magnitudes of the spectral shifts are about 15 nmfor 8T 8TOC (HT) and 8TOOC and 1881 2201 2368 817and 1062 nm for 8TCOC (TT) 8TOC (TT) 8TOC (HH)8TCOC (HH) and 8TCOC (HT) respectively The absorp-tionmaxima of all compounds are further shifted by the effectof the dimethyl sulfoxide solventThis might be related to thegradient electrostatic potential and donor effect of the OCH

3

CH2OCH3 and OOCH

3groups Further there is a variation

of the absorption maximum displacement for the samecompound (HT TT andHH) this is the result of the differentconfigurations that one compound can take In DMSO

Journal of Chemistry 9

200 300 400 500 600 700 800 900 1000 1100

0

20000

40000

60000

80000

100000

120000

140000

8TAbEm

200 300 400 500 600 700 800 900 1000 1100

0

20000

40000

60000

80000

100000

120000

140000

8OOCAbEm

120582 (nm) 120582 (nm)

Ener

gy (a

u)

Ener

gy (a

u)

Δ120582

200 300 400 500 600 700 800 900 1000 1100

0

20000

40000

60000

80000

100000

120000

140000

AbsorptionEmission

8TCOCHHabHHemHTab

HTemTTabTTem

300 400 500 600 700 800 900 1000 1100 1200 1300

0

20000

40000

60000

80000

100000

120000Absorption Emission

8TCOHHabHHemHTab

HTemTTabTTem

120582 (nm) 120582 (nm)

Ener

gy (a

u)

Ener

gy (a

u)

Figure 7 Calculated electronic absorption and emission of octamers units of 8T 8TOC (HH HT and TT) 8TOOC and 8TCOC (HH HTand TT) obtained by CAM-B3LYP6-31G(dp)

the calculated results for the absorptionmaximumof all com-pounds are located between 56823 and 40435 nm (Table 4)The peak positions of those molecules in DMSO show a redshift when compared to those measured experimentally [26]

43 Electronic Emission Spectra TD-DFTB3LYP6-31G(dp)has been used for optimized structures and CAM-B3LYP6-31G(dp) was used to calculate the excited state and to sim-ulate the emission spectra of the considered polymers andthe first singlet excited states are listed in Table 5 Similar tothe absorption spectra 119878

1rarr 1198780fluorescence peaks in emi-

ssion spectra (Figure 6) have the greatest oscillator strengthsin all molecules and exclusively arise fromHOMOrarr LUMO(120587 rarr 120587lowast electronic transition) Polymers with aromatic orheterocyclic units generally absorb light with wavelengths in

the range from 300 to 700 nm due to 120587 rarr 120587lowast transitionsThe excited states of their chromophores (excitons) releaseenergy radiatively as well as nonradiatively on returning tothe ground state [26] The radiative decay of excitons to theground state can emit visible light These excitons are alsoformed when a bias potential is applied to an emissive poly-mer sandwiched between an anode and a cathode [52]

The theoretical studies of our molecules can be used toderive the Stokes shifts the difference between the positionof the maxima band of the absorption and emission spectrain wavelength which is about 80 to 93 nm for the structures8T 8TOC (HH TT and HT) 8TCOC (TT) and 8TOOCbut that for the 8TCOC (HH) and 8TCOC (TT) is 149 nmAmong them the compound 8TCOC has a relatively largerStokes shift which indicates that electron transitions break

10 Journal of Chemistry

Table 5 Emission spectra in gaseous phase obtained by the TD-CAM-B3LYP6-31G(d) optimized geometries of 119878

1excited states for

the octamers

Compounds 120582 (nm) 119864 (eV) OS Δ120582 = 120582ab minus 120582em55797 222 30531

8T 43390 285 00000 79836564 339 00000

8TOC

HT62147 199 29482

817646113 268 0005742181 293 02710

HH63709 196 30801

925446191 268 0000040654 304 00000

TT62147 199 29482

881546113 268 0005742181 293 02710

8TCOC

TT53079 233 26028

911840043 309 0035434914 355 03253

HH54518 247 27840

1490040748 304 0027535560 348 00001

HT56951 217 30310

1766942626 290 0000136784 337 0007956106 220 29875

8TOOC 42641 290 00002 868436421 340 00000

the strong conjugate effect leading to remarkable changes inthe structure and reorganization energy as discussed above

5 Conclusions

In this study we have used the DFTB3LYP method to inves-tigate the theoretical analysis of the geometries and electronicproperties of some type-in-derivatives structure of polythio-phene The modification of chemical structures can greatlymodify and improve the electronic and optical properties ofpristine studied materials The electronic properties of theconjugated materials based on thiophene compounds havebeen computed using the 6-31G(dp) basis set at a densityfunctional B3LYP level in order to guide the synthesis ofnovel materials with specific electronic properties

In summary the conclusions are as follows

(i) TheUV-vis absorption properties have been obtainedby using TDCAM-B3LYP and TD-B3LYP calcula-tions The obtained absorption maximums are in therange of 350ndash550 nm

(ii) The HOMO level LUMO level and band gap ofthe studied compounds were well controlled by theacceptor strength The calculated band gap (119864gap) ofthe studiedmolecules was in the range of 191ndash302 eV

(iii) The calculated values of 119881oc of the studied moleculesrange from 016 eV to 091 eVPCBM these values aresufficient for a possible efficient electron injection

The theoretical results suggest that both the donor strengthand the stable geometry contribute significantly to the elec-tronic properties of the conjugated polymers Finally the pro-cedures of theoretical calculations can be employed to predictthe electronic properties of the other compounds and furtherto design novel materials for organic solar cells

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work has been supported by the Volubilis Program(no MA11248) and the convention CNRSTCNRS (ProjectChimie 1009) The authors are grateful to the ldquoAssociationMarocaine des Chimistes Theoriciensrdquo (AMCT) for its per-tinent help Guillermo Salgado-Moran gratefully acknowl-edges Si Mohamed Bouzzine for his invitation to participatein this work Daniel Glossman-Mitnik is a researcher ofCIMAV and CONACYT and acknowledges both institutionsfor partial support

References

[1] H-J Wang C-P Chen and R-J Jeng ldquoPolythiophenes com-prising conjugated pendants for polymer solar cells a reviewrdquoMaterials vol 7 no 4 pp 2411ndash2439 2014

[2] S Pesant P Boulanger M Cote and M Ernzerhof ldquoAb initiostudy of ladder-type polymers polythiophene and polypyrrolerdquoChemical Physics Letters vol 450 no 4ndash6 pp 329ndash334 2008

[3] J Roncali ldquoConjugated poly(thiophenes) synthesis functional-ization and applicationsrdquo Chemical Reviews vol 92 no 4 pp711ndash738 1992

[4] Y Wei C-C Chan J Tian G-W Jang and K F HsuehldquoElectrochemical polymerization of thiophenes in the presenceof bithiophene or terthiophene kinetics and mechanism of thepolymerizationrdquo Chemistry of Materials vol 3 no 5 pp 888ndash897 1991

[5] R M Souto Maior K Hinkelmann H Eckert and FWudl ldquoSynthesis and characterization of two regiochemi-cally defined poly(dialkylbithiophenes) a comparative studyrdquoMacromolecules vol 23 no 5 pp 1268ndash1279 1990

[6] M-A Sato and H Morii ldquoNuclear magnetic resonance stud-ies on electrochemically prepared poly(3-dodecylthiophene)rdquoMacromolecules vol 24 no 5 pp 1196ndash1200 1991

[7] Y-J Cheng S-H Yang and C-S Hsu ldquoSynthesis of conjugatedpolymers for organic solar cell applicationsrdquo Chemical Reviewsvol 109 no 11 pp 5868ndash5923 2009

[8] A C AlgunoW C Chung R V Bantaculo et al ldquoAb initio anddensity functional studies of polythiophene energy band gaprdquoNECTEC Technical Journal vol 2 no 9 pp 215ndash218 2001

[9] J Pei W-L Yu W Huang and A J Heeger ldquoA novel series ofefficient thiophene-based light-emitting conjugated polymersand application in polymer light-emitting diodesrdquo Macro-molecules vol 33 no 7 pp 2462ndash2471 2000

Journal of Chemistry 11

[10] A K Bakhshi ldquoTheoretical tailoring of electrically conductingpolymers some new resultsrdquoMaterials Science and EngineeringC vol 3 no 3-4 pp 249ndash255 1995

[11] M S Senevirathne A Nanayakkara and G K R Senadeera ldquoAtheoretical investigation of band gaps of conducting polymersmdashpolythiophene polypyrrole and polyfuranrdquo inProceedings of the23rd Technical Sessions vol 23 pp 47ndash53 Institute of PhysicsColombo Sri Lanka March 2007

[12] U Salzner J B Lagowski P G Pickup and R A PoirierldquoDesign of low band gap polymers employing density func-tional theorymdashhybrid functionals ameliorate band gap prob-lemrdquo Journal of Computational Chemistry vol 18 no 15 pp1943ndash1953 1997

[13] E Bundgaard and F C Krebs ldquoLow band gap polymers fororganic photovoltaicsrdquo Solar Energy Materials and Solar Cellsvol 91 no 11 pp 954ndash985 2007

[14] M J Frisch G W Trucks H B Schlegel et al ldquoGaussian 09Revision B04rdquo Gaussian Inc Wallingford Conn USA 2009

[15] M E Casida C Jamorski K C Casida and D R SalahubldquoMolecular excitation energies to high-lying bound states fromtime-dependent density-functional response theory charac-terization and correction of the time-dependent local den-sity approximation ionization thresholdrdquo Journal of ChemicalPhysics vol 108 no 11 pp 4439ndash4449 1998

[16] R E Stratmann G E Scuseria and M J Frisch ldquoAn efficientimplementation of time-dependent density-functional theoryfor the calculation of excitation energies of largemoleculesrdquoTheJournal of Chemical Physics vol 109 no 19 pp 8218ndash8224 1998

[17] T Yanai D P Tew and N C Handy ldquoA new hybrid exchange-correlation functional using the Coulomb-attenuating method(CAM-B3LYP)rdquo Chemical Physics Letters vol 393 no 1ndash3 pp51ndash57 2004

[18] J Preat ldquoPhotoinduced energy-transfer and electron-transferprocesses in dye-sensitized solar cells TDDFT insights fortriphenylamine dyesrdquoThe Journal of Physical Chemistry C vol114 no 39 pp 16716ndash16725 2010

[19] B Camino M de La Pierre and A M Ferrari ldquoPhotoelectro-chemical properties of the CT1 dye a DFT studyrdquo Journal ofMolecular Structure vol 1046 pp 116ndash123 2013

[20] A Irfan R Jin A G Al-Sehemi and A M Asiri ldquoQuantumchemical study of the donor-bridge-acceptor triphenylaminebased sensitizersrdquo Spectrochimica Acta Part A Molecular andBiomolecular Spectroscopy vol 110 pp 60ndash66 2013

[21] S Jungsuttiwong R Tarsang T Sudyoadsuk V Promarak PKhongpracha and S Namuangruk ldquoTheoretical study on noveldouble donor-based dyes used in high efficient dye-sensitizedsolar cells the application of TDDFT study to the electroninjection processrdquoOrganic Electronics PhysicsMaterials Appli-cations vol 14 no 3 pp 711ndash722 2013

[22] E J Meijer D M de Leeuw S Setayesh et al ldquoSolution-processed ambipolar organic field-effect transistors and invert-ersrdquo Nature Materials vol 2 no 10 pp 678ndash682 2003

[23] V Hernandez J T L Navarrete and J L Marcos ldquoElectronicstructure and lattice dynamics of polyfuranrdquo Synthetic Metalsvol 41 no 3 pp 789ndash792 1991

[24] F B Kooistra J Knol F Kastenberg et al ldquoIncreasing the opencircuit voltage of bulk-heterojunction solar cells by raising theLUMO level of the acceptorrdquo Organic Letters vol 9 no 4 pp551ndash554 2007

[25] J J M Halls J Cornil D A dos Santos et al ldquoCharge- andenergy-transfer processes at polymerpolymer interfaces a joint

experimental and theoretical studyrdquo Physical Review B vol 60no 8 pp 5721ndash5727 1999

[26] M Fall J-J Aaron and D Gningue-Sall ldquoLuminescence prop-erties of poly(3-methoxythiophene)mdashbithiophene compositeoligomersrdquo Journal of Fluorescence vol 10 no 2 pp 107ndash1112000

[27] M Cossi N Rega G Scalmani and V Barone ldquoEnergiesstructures and electronic properties of molecules in solutionwith the C-PCM solvation modelrdquo Journal of ComputationalChemistry vol 24 no 6 pp 669ndash681 2003

[28] V Barone and M Cossi ldquoQuantum calculation of molecularenergies and energy gradients in solution by a conductor solventmodelrdquoThe Journal of Physical Chemistry A vol 102 no 11 pp1995ndash2001 1998

[29] J F Pan S J Chua and W Huang ldquoQuantum calculationof molecular energies and energy gradients in solution by aconductor solventmodelrdquoChemical Physics Letters vol 363 no1-2 pp 18ndash24 2002

[30] U Salzner J B Lagowski P G Pickup and R A Poirier ldquoCom-parison of geometries and electronic structures of polyacety-lene polyborole polycyclopentadiene polypyrrole polyfuranpolysilole polyphosphole polythiophene polyselenophene andpolytellurophenerdquo Synthetic Metals vol 96 no 3 pp 177ndash1891998

[31] A Kraak and H Wynberg ldquoCharge-transfer interaction ofdithienyls and cyclopentadithiophenes with 135-trinitroben-zene (TNB)rdquo Tetrahedron vol 24 no 10 pp 3881ndash3885 1968

[32] M Dietrich and J Heinze ldquoPoly(441015840-dimethoxybithiophe-ne)mdasha new conducting polymer with extraordinary redox andoptical propertiesrdquo SyntheticMetals vol 41 no 1-2 pp 503ndash5061991

[33] H Zgou M Hamidi M Bouachrine and K Hasnaoui ldquoTheDFT study and opto-electronic properties of copolymers basedon thiophene and phenylenerdquo Physical and Chemical News vol32 pp 81ndash87 2006

[34] L Yang J-K Feng and A-M Ren ldquoTheoretical studies onthe electronic and optical properties of two thiophene-fluorenebased 120587-conjugated copolymersrdquo Polymer vol 46 no 24 pp10970ndash10981 2005

[35] J L Bredas R Silbey D S Boudreaux and R R ChanceldquoChain-length dependence of electronic and electrochemicalproperties of conjugated systems polyacetylene polypheny-lene polythiophene and polypyrrolerdquo Journal of the AmericanChemical Society vol 105 no 22 pp 6555ndash6559 1983

[36] D Fichou G Horowitz B Xu and F Garnier ldquoStoichiometriccontrol of the successive generation of the radical cation anddication of extended 120572-conjugated oligothiophenes a quantita-tive model for doped polythiophenerdquo Synthetic Metals vol 39no 2 pp 243ndash259 1990

[37] D Fichou G Horowitz Y Nishikitani and F Garnier ldquoSemi-conducting conjugated oligomers for molecular electronicsrdquoSynthetic Metals vol 28 no 1-2 pp 723ndash727 1989

[38] V May and O Kuhn Charge and Energy Transfer Dynamics inMolecular Systems Wiley-VCH Berlin Germany 2000

[39] GDennlerMC Scharber andC J Brabec ldquoPolymer-fullerenebulk-heterojunction solar cellsrdquoAdvancedMaterials vol 21 no13 pp 1323ndash1338 2009

[40] JW Chen andY Cao ldquoDevelopment of novel conjugated donorpolymers for high-efficiency bulk-heterojunction photovoltaicdevicesrdquoAccounts of Chemical Research vol 42 no 11 pp 1709ndash1718 2009

12 Journal of Chemistry

[41] Z Cai-Rong L Zi-Jiang C Yu-Hong C Hong-Shan W You-Zhi and Y Li-Hua ldquoDFT and TDDFT study on organic dyesensitizersD5DST andDSS for solar cellsrdquo Journal ofMolecularStructure THEOCHEM vol 899 no 1ndash3 pp 86ndash93 2009

[42] Y He H-Y Chen J Hou and Y Li ldquoIndene-C60bisadduct a

new acceptor for high-performance polymer solar cellsrdquo Journalof the American Chemical Society vol 132 no 4 pp 1377ndash13822010

[43] S Gunes H Neugebauer and N S Sariciftci ldquoConjugatedpolymer-based organic solar cellsrdquo Chemical Reviews vol 107no 4 pp 1324ndash1338 2007

[44] C J Brabec A Cravino D Meissner et al ldquoOrigin of theopen circuit voltage of plastic solar cellsrdquo Advanced FuntionalMaterials vol 11 no 5 pp 374ndash380 2001

[45] M C Scharber D Muhlbacher M Koppe et al ldquoDesign rulesfor donors in bulk-heterojunction solar cellsmdashtowards 10energy-conversion efficiencyrdquo Advanced Materials vol 18 no6 pp 789ndash794 2006

[46] A Gadisa M Svensson M R Andersson and O InganasldquoCorrelation between oxidation potential and open-circuitvoltage of composite solar cells based on blends of polythio-phenesfullerene derivativerdquoApplied Physics Letters vol 84 no9 pp 1609ndash1611 2004

[47] K Kaneto K Yoshino and Y Inuishi ldquoElectrical and opticalproperties of polythiophene prepared by electrochemical poly-merizationrdquo Solid State Communications vol 46 no 5 pp 389ndash391 1983

[48] D Jacquemin J Preat V Wathelet M Fontaine and E APerpete ldquoThioindigo dyes highly accurate visible spectra withTD-DFTrdquo Journal of the American Chemical Society vol 128 no6 pp 2072ndash2083 2006

[49] N Santhanamoorthi K Senthilkumar and P KolandaivelldquoTautomerization and solvent effects on the absorption andemission properties of the Schiff base NN1015840-bis(salicylidene)-p-phenylenediaminemdasha TDDFT studyrdquoMolecular Physics vol108 no 14 pp 1817ndash1827 2010

[50] J Vasudevan R T Stibrany J Bumby et al ldquoAn edge-over-edgeZn(II) bacteriochlorin dimer having an unshifted Q

119910bandThe

importance of 120587-overlaprdquo Journal of the American ChemicalSociety vol 118 no 46 pp 11676ndash11677 1996

[51] H Scheer and H H Inhoffen ldquoHydroporphyrins reactivityspectroscopy and hydroporphyrin analoguesrdquo in The Por-phyrins DDolphin Ed vol 2 pp 45ndash90 Academic Press NewYork NY USA 1978

[52] R H Friend R W Gymer A B Holmes et al ldquoElectrolumi-nescence in conjugated polymersrdquoNature vol 397 no 6715 pp121ndash128 1999

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

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Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

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Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

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The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Quantum Chemistry

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Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

4 Journal of Chemistry

1 2 3 4 5 6 71438

1439

1440

1441

1442

1443

1444

1445

1446

Bond number Bond number

8T8TOOC

1 2 3 4 5 6 7

1440

1444

1448

1452

1456

1460

8T8TCOC (HT)

8TCOC (TT)8TCOC (HH)

1 2 3 4 5 6 7

1432

1434

1436

1438

1440

1442

1444

1446

Bond number

8T8TOC (HT)

8TOC (HH)8TOC (TT)

Valu

es o

f len

gth

bond

(Aring)

Valu

es o

f len

gth

bond

(Aring)

Valu

es o

f len

gth

bond

(Aring)

Figure 2 Optimized C-C bond lengths interring of 8T 8TOOC 8TCOC (HH HT and TT) and 8TOC (HH HT and TT) in neutral stateswith the number of bonds studied by B3LY6-31G(dp) level

Table 3 Energy values of 119864LUMO (eV) 119864HOMO (eV) 119864gap (eV) and the open circuit voltage 119881oc (eV) of the studied molecules

Compounds 119864HOMO (eV) 119864LUMO (eV) 119864gap (eV) 119864gap (eV) exp 119881oc (eV)8T minus473 minus231 242 200 [22] 073

8TOOC minus416 minus170 246 016

8TCOC(HT) minus462 minus196 266 062(HH) minus490 minus188 302 090(TT) minus491 minus181 310 091

8TOC(HT) minus387 minus196 191 mdash(HH) minus389 minus182 207 mdash(TT) minus399 minus186 213 16 [23] mdash

PCBM [24 25] minus610 minus370

or lowers the HOMOLUMO energies in agreement withtheir electron donor character However these compoundshave a smaller energy gap (119864gap) than the unsubstituted one(8T) which is due to the presence of different substituents

as described previously [34 35] The band gap of 8TOC(HH TT and HT) is much smaller than that of the othersubstituted compoundsThismay be attributed to the numberof electron-donating methoxy side groups

Journal of Chemistry 5

1 2 3 4 5 6 7

120

130

140

150

160

170

180

190

200

210

Angle number Angle number

8T8TCOC (HT)

8TCOC (HH)8TCOC (TT)

1 2 3 4 5 6 7160

165

170

175

180

185

190

195

200

8T8TOC (HT)

8TOC (HH)8TOC (TT)

Valu

es o

f dih

edra

l ang

le (∘

)

Valu

es o

f dih

edra

l ang

le (∘

)

Figure 3 Optimized dihedral angle of 8T 8TCOC (HH HT and TT) and 8TOC (HH HT and TT) in neutral states with the number ofbonds studied by B3LY6-31G(dp) level

8T 8TOOC

8TCOC (HT) 8TCOC (TT)

8TCOC (HH)

8TOC (HT) 8TOC (HH)

8TOC (TT)

Figure 4 Optimized structures of the studied oligomers

6 Journal of Chemistry

HOMO LUMO

8T

8TOOC

8TOC (HT)

8TOC (TT)

8TOC (HH)

8TCOC (HT)

8TCOC (TT)

8TCOC (HH)

Figure 5 The contour plots of HOMO and LUMO orbitals of the studied compounds

33 Photovoltaic Properties Generally the most efficientpolymer solar cells are based on the bulk heterojunction(BHJ) structure of the blend of 120587-conjugated polymer donorsand fullerene derivative acceptors [7 36ndash40] Here we stud-ied the photovoltaic properties of polyalkyl thiophene with

[66]-phenyl-C61-butyric acidmethyl ester (PCBM) which isthe most widely used acceptor in solar cell devices The cor-responding structure of the photovoltaic devices is schemat-ically depicted in Figure 6 The difference in the HOMOenergy levels of 8T 8TCOC 8TOOC and the LUMO of

Journal of Chemistry 7En

ergy

(eV

)

HOMO

LUMO

minus65

minus60

minus55

minus50

minus45

minus40

minus35

minus30

minus25

minus20

minus15

PCBM

(C60

)

8TO

C (T

T)

8TO

C (H

T)

8TO

C (H

H)

8TCO

C (T

T)

8TCO

C (H

H)

8TCO

C (H

T)

8TO

OC8T

Voc

Egap

Figure 6 Band structure diagram illustrating the HOMO andLUMO energies of the studied compounds relative to the bandstructure of PCBM

PCBM was 073 eV 016 eV and 062 eV respectively butthe value of 8TOC is negative (Table 3) suggesting that thephotoexcited electron transfer from the study compounds toPCBM may be sufficiently efficient to be useful in photo-voltaic devices [24 41 42]

In principle the optimization of polymer-fullerene solarcells is based on fine-tuning the electronic properties andinteractions of the donor and acceptor components so as toabsorb themaximumquantity of light and generate the great-est number of free charges with minimal concomitant loss ofenergy and transport the charges to the electrodes Howeverit is necessary to know the ideal electronic characteristics thateach component should have for the design of the next gen-eration high-efficiency photovoltaic systems The two com-ponents required in these devices for electronic optimizationare a soluble fullerene (generally a C60 derivative) acceptorand a polymeric donor that can be processed in solutionFullerenes are currently considered to be the ideal acceptorsfor organic solar cells for several reasons First they have anenergetically deep-lying LUMO which endows the moleculewith a very high electron affinity relative to the numerouspotential organic donors [25]

It is apparent that the active layer donor-acceptor com-posite governs all aspects of the mechanism with theexception of charge collection which is based on the elec-tronic interface between the active layer composite and therespective electrode Besides the fundamental mechanisticsteps the open circuit voltage (119881oc) is also governed by theenergetic relationship between the donor and the acceptor(Figure 6) rather than the work functions of the cathode andanode as would be expected from a simplistic view of thesediode devices Specifically the energy difference between theHOMO of the donor and the LUMO of the acceptor is foundto be very closely correlated with the 119881oc value [43ndash45]

The maximum open circuit voltage (119881oc) of the BHJ solarcell is related to the difference between the highest occupiedmolecular orbital (HOMO) of the electron donor and theLUMO of the electron acceptor taking into account theenergy lost during the photocharge generation [46] The the-oretical values of open circuit voltage119881oc have been calculatedfrom the following expression

119881oc =10038161003816100381610038161003816119864HOMO

(Donor)10038161003816100381610038161003816minus

10038161003816100381610038161003816119864LUMO

(Acceptor)10038161003816100381610038161003816minus 03 (2)

Moreover these compounds have absorption maxima in theneighborhood of 400ndash540 nm (Table 4) which is the opti-mum range of absorption (UV-visible) for photovoltaic cellsIn addition they have an energy gap of the order of 200 eV(Table 3) for the elevation of the electron from the HOMO tothe LUMO orbitals This characteristic allows us to promotethese compounds for the production of solar cells Thesevalues are sufficient for a possible efficient electron injectionsystem Therefore all the studied molecules can be used asorganic solar cell components because the electron injectionprocess from the excited molecule to the conduction bandof the acceptor (PCBM) and the subsequent regeneration ispossible in photovoltaic cells

4 Optoelectronic Parameters

41 Electronic Absorption Spectra For a better understandingof the electronic properties of thiophene-based moleculesthe excitation energy based on the first and second singlet-singlet electronic transitions has been studied In recentyears time dependent density functional theory (TD-DFT)has emerged as a reliable standard tool for the theoreticaltreatment of electronic excitation spectra and recent worksdemonstrate better accuracy for a wide range of systems [4748] The TD-DFTB3LYP6-31G(dp) has been used on thebasis of the optimized geometry The nature and the energyof the singlet-singlet electronic transitions of all the oligomersin all series under study are reported in Table 4 All electronictransitions are 120587 rarr 120587lowast type and no localized electronictransitions are exhibited among the calculated singlet-singlettransition Table 4 summarizes the transition energies ofabsorption spectra and oscillator strength Two interestingtrends in oscillator strength can be found in all series ofcompounds the oscillator strength OS of 119878

0rarr 1198781is the

overwhelmingly largest of all the series of polymersAccording to Table 4 we note an excitation energy of

about 2 eV for all compounds studied In addition absorp-tion maxima were located in the 400ndash540 nm range for allcompounds indicating all molecules have only one band inthe visible region (120582abs gt 400 nm) The absorption spectra ofthese compounds showed a major absorption band assignedto the 120587 rarr 120587lowast transition local electron

According to the transition character most of the com-pounds show the HOMOrarr LUMO transition as the firstsinglet excitationThemaximum (120582max) wavelengths for UV-vis absorption spectra of all compounds simulated are shownin Figure 7 The calculated 120582max by TD-DFT-B3LY and TD-CAM-B3LYP is different by about 99 nm = 120582max(B3LYP) minus120582max(CAM-B3LYP)

8 Journal of Chemistry

Table 4 Excitation energy valuesΔ119864 for the studied compounds obtained by TD-DFTCAM-B3LYP TD-DFT B3LYPwith 6-31G (dp) level

Compounds 120582 (nm) Exp [26] TD-B3LYP TD-CAM-B3LYP (DMSO) TD-CAM-B3LYP120582 (nm) 119864 (eV) (OS) 120582 (nm) 119864 (eV) (OS) 120582 (nm) 119864 (eV) (OS) Molecular orbital

8T 44864459 192 (29063) 49362 251 (30912) 47807 259 (29578)

Hrarr L (063)55329 224 (0000) 41015 302 (0000) 39233 310 (00000)53639 231 (0000) 32315 383 (0000) 32300 383 (00000)

8TOC

HT71723 172 (14020) 54514 227 (32032) 52971 234 (29449)

Hrarr L (064)55736 222 (16056) 43788 283 (00002) 42071 294 (00021)51485 240 (00072) 36582 338 (02814) 36469 339 (02123)

HH66172 187 (28471) 56823 218 (31391) 54455 227 (30037)

Hrarr L (064)465 55155 224 (0000) 45348 273 (0000) 43004 288 (0000)45297 273 (0000) 36233 342 (0000) 36074 343 (0000)

TT64658 191 (28253) 55533 223 (30750) 53332 232 (29676)

Hrarr L (064)53795 230 (0000) 44230 280 (00041) 42118 294 (00035)

47532 260 (0000) 35593 348(00004) 35462 349 (00001)

8TCOC

HT52952 234 (24562) 45023 275 (25260) 43961 282 (28030)

Hrarr L (062)44536 278 (00966) 38134 325 (00568) 36861 336 (00488)42203 293 (00397) 33152 373 (03015) 32230 384 (02428)

HH47208 262 (21440) 40435 306 (26989) 39618 312 (25865)

Hrarr L (062)mdash 40834 303 (00008) 35682 347 (00998) 34623 358 (00852)

39627 312 (00661) 31908 388 (02093) 28581 433 (00000)

TT46712 265 (20300) 41163 301 (27553) 39282 315 (24701)

Hrarr L (062)40397 306 (00042) 36159 342 (00509) 34187 362 (00641)39818 311 (00434) 32429 382 (03900) 31340 395 (04098)

8TOOC mdash57329 216 (26859) 48934 253 (30704) 47422 261 (29274)

Hrarr L (064)47995 258 (0000) 40835 305 (0000) 39248 315 (00001)44588 278 (0000) 34835 355 (02826) 33704 367 (02340)

The prediction of the excitation energies and oscillatorstrengths by using the CAM-B3LYP is in better agreementwith the experimental results [49 50] than is found forB3LYP because the CAM- (Coulomb-attenuating method-)B3LYP also takes account of the long-range corrections fordescribing the long 120587-conjugation [51]The results are shownin Table 4 and we note that the excitation energy values Δ119864obtained by TD-DFTCAM-B3LYP6-31G(dp) level are inagreement with those obtained by the methods DFTB3LYP6-31G(dp) level therefore theCAM-B3LYP functional is veryuseful for predicting the excitation energies and oscillatorstrengths The values calculated using the TD-DFT CAM-B3LYP function of our compounds in vacuo for predictingthe excitation energies and oscillator strengths are listed inTable 4 The TDCAM-B3LYP6-31G(dp) method was alsoemployed to simulate the optical property of the compounds

42 Effect of Solvent Solvent effects attract considerable atte-ntion because most of the chemical processes occur in thesolution phaseThe solvent effects are included here to ensure

that the calculations are compatible with the typical con-ditions The effects of chemical environment are discussedfurther as follows In order to study the effect of solvents onthe ground state molecular geometry excitation energies andmaximum absorption quantum chemical calculations on thestudied molecules were carried out in vacuum in dimethylsulfoxide (DMSO) The longest wavelength peaks from C-PCM-TD-CAM-B3LYP6-31G(dp) results are shifted com-pared to the corresponding ones using the TD-CAM-B3LYPresults The magnitudes of the spectral shifts are about 15 nmfor 8T 8TOC (HT) and 8TOOC and 1881 2201 2368 817and 1062 nm for 8TCOC (TT) 8TOC (TT) 8TOC (HH)8TCOC (HH) and 8TCOC (HT) respectively The absorp-tionmaxima of all compounds are further shifted by the effectof the dimethyl sulfoxide solventThis might be related to thegradient electrostatic potential and donor effect of the OCH

3

CH2OCH3 and OOCH

3groups Further there is a variation

of the absorption maximum displacement for the samecompound (HT TT andHH) this is the result of the differentconfigurations that one compound can take In DMSO

Journal of Chemistry 9

200 300 400 500 600 700 800 900 1000 1100

0

20000

40000

60000

80000

100000

120000

140000

8TAbEm

200 300 400 500 600 700 800 900 1000 1100

0

20000

40000

60000

80000

100000

120000

140000

8OOCAbEm

120582 (nm) 120582 (nm)

Ener

gy (a

u)

Ener

gy (a

u)

Δ120582

200 300 400 500 600 700 800 900 1000 1100

0

20000

40000

60000

80000

100000

120000

140000

AbsorptionEmission

8TCOCHHabHHemHTab

HTemTTabTTem

300 400 500 600 700 800 900 1000 1100 1200 1300

0

20000

40000

60000

80000

100000

120000Absorption Emission

8TCOHHabHHemHTab

HTemTTabTTem

120582 (nm) 120582 (nm)

Ener

gy (a

u)

Ener

gy (a

u)

Figure 7 Calculated electronic absorption and emission of octamers units of 8T 8TOC (HH HT and TT) 8TOOC and 8TCOC (HH HTand TT) obtained by CAM-B3LYP6-31G(dp)

the calculated results for the absorptionmaximumof all com-pounds are located between 56823 and 40435 nm (Table 4)The peak positions of those molecules in DMSO show a redshift when compared to those measured experimentally [26]

43 Electronic Emission Spectra TD-DFTB3LYP6-31G(dp)has been used for optimized structures and CAM-B3LYP6-31G(dp) was used to calculate the excited state and to sim-ulate the emission spectra of the considered polymers andthe first singlet excited states are listed in Table 5 Similar tothe absorption spectra 119878

1rarr 1198780fluorescence peaks in emi-

ssion spectra (Figure 6) have the greatest oscillator strengthsin all molecules and exclusively arise fromHOMOrarr LUMO(120587 rarr 120587lowast electronic transition) Polymers with aromatic orheterocyclic units generally absorb light with wavelengths in

the range from 300 to 700 nm due to 120587 rarr 120587lowast transitionsThe excited states of their chromophores (excitons) releaseenergy radiatively as well as nonradiatively on returning tothe ground state [26] The radiative decay of excitons to theground state can emit visible light These excitons are alsoformed when a bias potential is applied to an emissive poly-mer sandwiched between an anode and a cathode [52]

The theoretical studies of our molecules can be used toderive the Stokes shifts the difference between the positionof the maxima band of the absorption and emission spectrain wavelength which is about 80 to 93 nm for the structures8T 8TOC (HH TT and HT) 8TCOC (TT) and 8TOOCbut that for the 8TCOC (HH) and 8TCOC (TT) is 149 nmAmong them the compound 8TCOC has a relatively largerStokes shift which indicates that electron transitions break

10 Journal of Chemistry

Table 5 Emission spectra in gaseous phase obtained by the TD-CAM-B3LYP6-31G(d) optimized geometries of 119878

1excited states for

the octamers

Compounds 120582 (nm) 119864 (eV) OS Δ120582 = 120582ab minus 120582em55797 222 30531

8T 43390 285 00000 79836564 339 00000

8TOC

HT62147 199 29482

817646113 268 0005742181 293 02710

HH63709 196 30801

925446191 268 0000040654 304 00000

TT62147 199 29482

881546113 268 0005742181 293 02710

8TCOC

TT53079 233 26028

911840043 309 0035434914 355 03253

HH54518 247 27840

1490040748 304 0027535560 348 00001

HT56951 217 30310

1766942626 290 0000136784 337 0007956106 220 29875

8TOOC 42641 290 00002 868436421 340 00000

the strong conjugate effect leading to remarkable changes inthe structure and reorganization energy as discussed above

5 Conclusions

In this study we have used the DFTB3LYP method to inves-tigate the theoretical analysis of the geometries and electronicproperties of some type-in-derivatives structure of polythio-phene The modification of chemical structures can greatlymodify and improve the electronic and optical properties ofpristine studied materials The electronic properties of theconjugated materials based on thiophene compounds havebeen computed using the 6-31G(dp) basis set at a densityfunctional B3LYP level in order to guide the synthesis ofnovel materials with specific electronic properties

In summary the conclusions are as follows

(i) TheUV-vis absorption properties have been obtainedby using TDCAM-B3LYP and TD-B3LYP calcula-tions The obtained absorption maximums are in therange of 350ndash550 nm

(ii) The HOMO level LUMO level and band gap ofthe studied compounds were well controlled by theacceptor strength The calculated band gap (119864gap) ofthe studiedmolecules was in the range of 191ndash302 eV

(iii) The calculated values of 119881oc of the studied moleculesrange from 016 eV to 091 eVPCBM these values aresufficient for a possible efficient electron injection

The theoretical results suggest that both the donor strengthand the stable geometry contribute significantly to the elec-tronic properties of the conjugated polymers Finally the pro-cedures of theoretical calculations can be employed to predictthe electronic properties of the other compounds and furtherto design novel materials for organic solar cells

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work has been supported by the Volubilis Program(no MA11248) and the convention CNRSTCNRS (ProjectChimie 1009) The authors are grateful to the ldquoAssociationMarocaine des Chimistes Theoriciensrdquo (AMCT) for its per-tinent help Guillermo Salgado-Moran gratefully acknowl-edges Si Mohamed Bouzzine for his invitation to participatein this work Daniel Glossman-Mitnik is a researcher ofCIMAV and CONACYT and acknowledges both institutionsfor partial support

References

[1] H-J Wang C-P Chen and R-J Jeng ldquoPolythiophenes com-prising conjugated pendants for polymer solar cells a reviewrdquoMaterials vol 7 no 4 pp 2411ndash2439 2014

[2] S Pesant P Boulanger M Cote and M Ernzerhof ldquoAb initiostudy of ladder-type polymers polythiophene and polypyrrolerdquoChemical Physics Letters vol 450 no 4ndash6 pp 329ndash334 2008

[3] J Roncali ldquoConjugated poly(thiophenes) synthesis functional-ization and applicationsrdquo Chemical Reviews vol 92 no 4 pp711ndash738 1992

[4] Y Wei C-C Chan J Tian G-W Jang and K F HsuehldquoElectrochemical polymerization of thiophenes in the presenceof bithiophene or terthiophene kinetics and mechanism of thepolymerizationrdquo Chemistry of Materials vol 3 no 5 pp 888ndash897 1991

[5] R M Souto Maior K Hinkelmann H Eckert and FWudl ldquoSynthesis and characterization of two regiochemi-cally defined poly(dialkylbithiophenes) a comparative studyrdquoMacromolecules vol 23 no 5 pp 1268ndash1279 1990

[6] M-A Sato and H Morii ldquoNuclear magnetic resonance stud-ies on electrochemically prepared poly(3-dodecylthiophene)rdquoMacromolecules vol 24 no 5 pp 1196ndash1200 1991

[7] Y-J Cheng S-H Yang and C-S Hsu ldquoSynthesis of conjugatedpolymers for organic solar cell applicationsrdquo Chemical Reviewsvol 109 no 11 pp 5868ndash5923 2009

[8] A C AlgunoW C Chung R V Bantaculo et al ldquoAb initio anddensity functional studies of polythiophene energy band gaprdquoNECTEC Technical Journal vol 2 no 9 pp 215ndash218 2001

[9] J Pei W-L Yu W Huang and A J Heeger ldquoA novel series ofefficient thiophene-based light-emitting conjugated polymersand application in polymer light-emitting diodesrdquo Macro-molecules vol 33 no 7 pp 2462ndash2471 2000

Journal of Chemistry 11

[10] A K Bakhshi ldquoTheoretical tailoring of electrically conductingpolymers some new resultsrdquoMaterials Science and EngineeringC vol 3 no 3-4 pp 249ndash255 1995

[11] M S Senevirathne A Nanayakkara and G K R Senadeera ldquoAtheoretical investigation of band gaps of conducting polymersmdashpolythiophene polypyrrole and polyfuranrdquo inProceedings of the23rd Technical Sessions vol 23 pp 47ndash53 Institute of PhysicsColombo Sri Lanka March 2007

[12] U Salzner J B Lagowski P G Pickup and R A PoirierldquoDesign of low band gap polymers employing density func-tional theorymdashhybrid functionals ameliorate band gap prob-lemrdquo Journal of Computational Chemistry vol 18 no 15 pp1943ndash1953 1997

[13] E Bundgaard and F C Krebs ldquoLow band gap polymers fororganic photovoltaicsrdquo Solar Energy Materials and Solar Cellsvol 91 no 11 pp 954ndash985 2007

[14] M J Frisch G W Trucks H B Schlegel et al ldquoGaussian 09Revision B04rdquo Gaussian Inc Wallingford Conn USA 2009

[15] M E Casida C Jamorski K C Casida and D R SalahubldquoMolecular excitation energies to high-lying bound states fromtime-dependent density-functional response theory charac-terization and correction of the time-dependent local den-sity approximation ionization thresholdrdquo Journal of ChemicalPhysics vol 108 no 11 pp 4439ndash4449 1998

[16] R E Stratmann G E Scuseria and M J Frisch ldquoAn efficientimplementation of time-dependent density-functional theoryfor the calculation of excitation energies of largemoleculesrdquoTheJournal of Chemical Physics vol 109 no 19 pp 8218ndash8224 1998

[17] T Yanai D P Tew and N C Handy ldquoA new hybrid exchange-correlation functional using the Coulomb-attenuating method(CAM-B3LYP)rdquo Chemical Physics Letters vol 393 no 1ndash3 pp51ndash57 2004

[18] J Preat ldquoPhotoinduced energy-transfer and electron-transferprocesses in dye-sensitized solar cells TDDFT insights fortriphenylamine dyesrdquoThe Journal of Physical Chemistry C vol114 no 39 pp 16716ndash16725 2010

[19] B Camino M de La Pierre and A M Ferrari ldquoPhotoelectro-chemical properties of the CT1 dye a DFT studyrdquo Journal ofMolecular Structure vol 1046 pp 116ndash123 2013

[20] A Irfan R Jin A G Al-Sehemi and A M Asiri ldquoQuantumchemical study of the donor-bridge-acceptor triphenylaminebased sensitizersrdquo Spectrochimica Acta Part A Molecular andBiomolecular Spectroscopy vol 110 pp 60ndash66 2013

[21] S Jungsuttiwong R Tarsang T Sudyoadsuk V Promarak PKhongpracha and S Namuangruk ldquoTheoretical study on noveldouble donor-based dyes used in high efficient dye-sensitizedsolar cells the application of TDDFT study to the electroninjection processrdquoOrganic Electronics PhysicsMaterials Appli-cations vol 14 no 3 pp 711ndash722 2013

[22] E J Meijer D M de Leeuw S Setayesh et al ldquoSolution-processed ambipolar organic field-effect transistors and invert-ersrdquo Nature Materials vol 2 no 10 pp 678ndash682 2003

[23] V Hernandez J T L Navarrete and J L Marcos ldquoElectronicstructure and lattice dynamics of polyfuranrdquo Synthetic Metalsvol 41 no 3 pp 789ndash792 1991

[24] F B Kooistra J Knol F Kastenberg et al ldquoIncreasing the opencircuit voltage of bulk-heterojunction solar cells by raising theLUMO level of the acceptorrdquo Organic Letters vol 9 no 4 pp551ndash554 2007

[25] J J M Halls J Cornil D A dos Santos et al ldquoCharge- andenergy-transfer processes at polymerpolymer interfaces a joint

experimental and theoretical studyrdquo Physical Review B vol 60no 8 pp 5721ndash5727 1999

[26] M Fall J-J Aaron and D Gningue-Sall ldquoLuminescence prop-erties of poly(3-methoxythiophene)mdashbithiophene compositeoligomersrdquo Journal of Fluorescence vol 10 no 2 pp 107ndash1112000

[27] M Cossi N Rega G Scalmani and V Barone ldquoEnergiesstructures and electronic properties of molecules in solutionwith the C-PCM solvation modelrdquo Journal of ComputationalChemistry vol 24 no 6 pp 669ndash681 2003

[28] V Barone and M Cossi ldquoQuantum calculation of molecularenergies and energy gradients in solution by a conductor solventmodelrdquoThe Journal of Physical Chemistry A vol 102 no 11 pp1995ndash2001 1998

[29] J F Pan S J Chua and W Huang ldquoQuantum calculationof molecular energies and energy gradients in solution by aconductor solventmodelrdquoChemical Physics Letters vol 363 no1-2 pp 18ndash24 2002

[30] U Salzner J B Lagowski P G Pickup and R A Poirier ldquoCom-parison of geometries and electronic structures of polyacety-lene polyborole polycyclopentadiene polypyrrole polyfuranpolysilole polyphosphole polythiophene polyselenophene andpolytellurophenerdquo Synthetic Metals vol 96 no 3 pp 177ndash1891998

[31] A Kraak and H Wynberg ldquoCharge-transfer interaction ofdithienyls and cyclopentadithiophenes with 135-trinitroben-zene (TNB)rdquo Tetrahedron vol 24 no 10 pp 3881ndash3885 1968

[32] M Dietrich and J Heinze ldquoPoly(441015840-dimethoxybithiophe-ne)mdasha new conducting polymer with extraordinary redox andoptical propertiesrdquo SyntheticMetals vol 41 no 1-2 pp 503ndash5061991

[33] H Zgou M Hamidi M Bouachrine and K Hasnaoui ldquoTheDFT study and opto-electronic properties of copolymers basedon thiophene and phenylenerdquo Physical and Chemical News vol32 pp 81ndash87 2006

[34] L Yang J-K Feng and A-M Ren ldquoTheoretical studies onthe electronic and optical properties of two thiophene-fluorenebased 120587-conjugated copolymersrdquo Polymer vol 46 no 24 pp10970ndash10981 2005

[35] J L Bredas R Silbey D S Boudreaux and R R ChanceldquoChain-length dependence of electronic and electrochemicalproperties of conjugated systems polyacetylene polypheny-lene polythiophene and polypyrrolerdquo Journal of the AmericanChemical Society vol 105 no 22 pp 6555ndash6559 1983

[36] D Fichou G Horowitz B Xu and F Garnier ldquoStoichiometriccontrol of the successive generation of the radical cation anddication of extended 120572-conjugated oligothiophenes a quantita-tive model for doped polythiophenerdquo Synthetic Metals vol 39no 2 pp 243ndash259 1990

[37] D Fichou G Horowitz Y Nishikitani and F Garnier ldquoSemi-conducting conjugated oligomers for molecular electronicsrdquoSynthetic Metals vol 28 no 1-2 pp 723ndash727 1989

[38] V May and O Kuhn Charge and Energy Transfer Dynamics inMolecular Systems Wiley-VCH Berlin Germany 2000

[39] GDennlerMC Scharber andC J Brabec ldquoPolymer-fullerenebulk-heterojunction solar cellsrdquoAdvancedMaterials vol 21 no13 pp 1323ndash1338 2009

[40] JW Chen andY Cao ldquoDevelopment of novel conjugated donorpolymers for high-efficiency bulk-heterojunction photovoltaicdevicesrdquoAccounts of Chemical Research vol 42 no 11 pp 1709ndash1718 2009

12 Journal of Chemistry

[41] Z Cai-Rong L Zi-Jiang C Yu-Hong C Hong-Shan W You-Zhi and Y Li-Hua ldquoDFT and TDDFT study on organic dyesensitizersD5DST andDSS for solar cellsrdquo Journal ofMolecularStructure THEOCHEM vol 899 no 1ndash3 pp 86ndash93 2009

[42] Y He H-Y Chen J Hou and Y Li ldquoIndene-C60bisadduct a

new acceptor for high-performance polymer solar cellsrdquo Journalof the American Chemical Society vol 132 no 4 pp 1377ndash13822010

[43] S Gunes H Neugebauer and N S Sariciftci ldquoConjugatedpolymer-based organic solar cellsrdquo Chemical Reviews vol 107no 4 pp 1324ndash1338 2007

[44] C J Brabec A Cravino D Meissner et al ldquoOrigin of theopen circuit voltage of plastic solar cellsrdquo Advanced FuntionalMaterials vol 11 no 5 pp 374ndash380 2001

[45] M C Scharber D Muhlbacher M Koppe et al ldquoDesign rulesfor donors in bulk-heterojunction solar cellsmdashtowards 10energy-conversion efficiencyrdquo Advanced Materials vol 18 no6 pp 789ndash794 2006

[46] A Gadisa M Svensson M R Andersson and O InganasldquoCorrelation between oxidation potential and open-circuitvoltage of composite solar cells based on blends of polythio-phenesfullerene derivativerdquoApplied Physics Letters vol 84 no9 pp 1609ndash1611 2004

[47] K Kaneto K Yoshino and Y Inuishi ldquoElectrical and opticalproperties of polythiophene prepared by electrochemical poly-merizationrdquo Solid State Communications vol 46 no 5 pp 389ndash391 1983

[48] D Jacquemin J Preat V Wathelet M Fontaine and E APerpete ldquoThioindigo dyes highly accurate visible spectra withTD-DFTrdquo Journal of the American Chemical Society vol 128 no6 pp 2072ndash2083 2006

[49] N Santhanamoorthi K Senthilkumar and P KolandaivelldquoTautomerization and solvent effects on the absorption andemission properties of the Schiff base NN1015840-bis(salicylidene)-p-phenylenediaminemdasha TDDFT studyrdquoMolecular Physics vol108 no 14 pp 1817ndash1827 2010

[50] J Vasudevan R T Stibrany J Bumby et al ldquoAn edge-over-edgeZn(II) bacteriochlorin dimer having an unshifted Q

119910bandThe

importance of 120587-overlaprdquo Journal of the American ChemicalSociety vol 118 no 46 pp 11676ndash11677 1996

[51] H Scheer and H H Inhoffen ldquoHydroporphyrins reactivityspectroscopy and hydroporphyrin analoguesrdquo in The Por-phyrins DDolphin Ed vol 2 pp 45ndash90 Academic Press NewYork NY USA 1978

[52] R H Friend R W Gymer A B Holmes et al ldquoElectrolumi-nescence in conjugated polymersrdquoNature vol 397 no 6715 pp121ndash128 1999

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

Journal of Chemistry 5

1 2 3 4 5 6 7

120

130

140

150

160

170

180

190

200

210

Angle number Angle number

8T8TCOC (HT)

8TCOC (HH)8TCOC (TT)

1 2 3 4 5 6 7160

165

170

175

180

185

190

195

200

8T8TOC (HT)

8TOC (HH)8TOC (TT)

Valu

es o

f dih

edra

l ang

le (∘

)

Valu

es o

f dih

edra

l ang

le (∘

)

Figure 3 Optimized dihedral angle of 8T 8TCOC (HH HT and TT) and 8TOC (HH HT and TT) in neutral states with the number ofbonds studied by B3LY6-31G(dp) level

8T 8TOOC

8TCOC (HT) 8TCOC (TT)

8TCOC (HH)

8TOC (HT) 8TOC (HH)

8TOC (TT)

Figure 4 Optimized structures of the studied oligomers

6 Journal of Chemistry

HOMO LUMO

8T

8TOOC

8TOC (HT)

8TOC (TT)

8TOC (HH)

8TCOC (HT)

8TCOC (TT)

8TCOC (HH)

Figure 5 The contour plots of HOMO and LUMO orbitals of the studied compounds

33 Photovoltaic Properties Generally the most efficientpolymer solar cells are based on the bulk heterojunction(BHJ) structure of the blend of 120587-conjugated polymer donorsand fullerene derivative acceptors [7 36ndash40] Here we stud-ied the photovoltaic properties of polyalkyl thiophene with

[66]-phenyl-C61-butyric acidmethyl ester (PCBM) which isthe most widely used acceptor in solar cell devices The cor-responding structure of the photovoltaic devices is schemat-ically depicted in Figure 6 The difference in the HOMOenergy levels of 8T 8TCOC 8TOOC and the LUMO of

Journal of Chemistry 7En

ergy

(eV

)

HOMO

LUMO

minus65

minus60

minus55

minus50

minus45

minus40

minus35

minus30

minus25

minus20

minus15

PCBM

(C60

)

8TO

C (T

T)

8TO

C (H

T)

8TO

C (H

H)

8TCO

C (T

T)

8TCO

C (H

H)

8TCO

C (H

T)

8TO

OC8T

Voc

Egap

Figure 6 Band structure diagram illustrating the HOMO andLUMO energies of the studied compounds relative to the bandstructure of PCBM

PCBM was 073 eV 016 eV and 062 eV respectively butthe value of 8TOC is negative (Table 3) suggesting that thephotoexcited electron transfer from the study compounds toPCBM may be sufficiently efficient to be useful in photo-voltaic devices [24 41 42]

In principle the optimization of polymer-fullerene solarcells is based on fine-tuning the electronic properties andinteractions of the donor and acceptor components so as toabsorb themaximumquantity of light and generate the great-est number of free charges with minimal concomitant loss ofenergy and transport the charges to the electrodes Howeverit is necessary to know the ideal electronic characteristics thateach component should have for the design of the next gen-eration high-efficiency photovoltaic systems The two com-ponents required in these devices for electronic optimizationare a soluble fullerene (generally a C60 derivative) acceptorand a polymeric donor that can be processed in solutionFullerenes are currently considered to be the ideal acceptorsfor organic solar cells for several reasons First they have anenergetically deep-lying LUMO which endows the moleculewith a very high electron affinity relative to the numerouspotential organic donors [25]

It is apparent that the active layer donor-acceptor com-posite governs all aspects of the mechanism with theexception of charge collection which is based on the elec-tronic interface between the active layer composite and therespective electrode Besides the fundamental mechanisticsteps the open circuit voltage (119881oc) is also governed by theenergetic relationship between the donor and the acceptor(Figure 6) rather than the work functions of the cathode andanode as would be expected from a simplistic view of thesediode devices Specifically the energy difference between theHOMO of the donor and the LUMO of the acceptor is foundto be very closely correlated with the 119881oc value [43ndash45]

The maximum open circuit voltage (119881oc) of the BHJ solarcell is related to the difference between the highest occupiedmolecular orbital (HOMO) of the electron donor and theLUMO of the electron acceptor taking into account theenergy lost during the photocharge generation [46] The the-oretical values of open circuit voltage119881oc have been calculatedfrom the following expression

119881oc =10038161003816100381610038161003816119864HOMO

(Donor)10038161003816100381610038161003816minus

10038161003816100381610038161003816119864LUMO

(Acceptor)10038161003816100381610038161003816minus 03 (2)

Moreover these compounds have absorption maxima in theneighborhood of 400ndash540 nm (Table 4) which is the opti-mum range of absorption (UV-visible) for photovoltaic cellsIn addition they have an energy gap of the order of 200 eV(Table 3) for the elevation of the electron from the HOMO tothe LUMO orbitals This characteristic allows us to promotethese compounds for the production of solar cells Thesevalues are sufficient for a possible efficient electron injectionsystem Therefore all the studied molecules can be used asorganic solar cell components because the electron injectionprocess from the excited molecule to the conduction bandof the acceptor (PCBM) and the subsequent regeneration ispossible in photovoltaic cells

4 Optoelectronic Parameters

41 Electronic Absorption Spectra For a better understandingof the electronic properties of thiophene-based moleculesthe excitation energy based on the first and second singlet-singlet electronic transitions has been studied In recentyears time dependent density functional theory (TD-DFT)has emerged as a reliable standard tool for the theoreticaltreatment of electronic excitation spectra and recent worksdemonstrate better accuracy for a wide range of systems [4748] The TD-DFTB3LYP6-31G(dp) has been used on thebasis of the optimized geometry The nature and the energyof the singlet-singlet electronic transitions of all the oligomersin all series under study are reported in Table 4 All electronictransitions are 120587 rarr 120587lowast type and no localized electronictransitions are exhibited among the calculated singlet-singlettransition Table 4 summarizes the transition energies ofabsorption spectra and oscillator strength Two interestingtrends in oscillator strength can be found in all series ofcompounds the oscillator strength OS of 119878

0rarr 1198781is the

overwhelmingly largest of all the series of polymersAccording to Table 4 we note an excitation energy of

about 2 eV for all compounds studied In addition absorp-tion maxima were located in the 400ndash540 nm range for allcompounds indicating all molecules have only one band inthe visible region (120582abs gt 400 nm) The absorption spectra ofthese compounds showed a major absorption band assignedto the 120587 rarr 120587lowast transition local electron

According to the transition character most of the com-pounds show the HOMOrarr LUMO transition as the firstsinglet excitationThemaximum (120582max) wavelengths for UV-vis absorption spectra of all compounds simulated are shownin Figure 7 The calculated 120582max by TD-DFT-B3LY and TD-CAM-B3LYP is different by about 99 nm = 120582max(B3LYP) minus120582max(CAM-B3LYP)

8 Journal of Chemistry

Table 4 Excitation energy valuesΔ119864 for the studied compounds obtained by TD-DFTCAM-B3LYP TD-DFT B3LYPwith 6-31G (dp) level

Compounds 120582 (nm) Exp [26] TD-B3LYP TD-CAM-B3LYP (DMSO) TD-CAM-B3LYP120582 (nm) 119864 (eV) (OS) 120582 (nm) 119864 (eV) (OS) 120582 (nm) 119864 (eV) (OS) Molecular orbital

8T 44864459 192 (29063) 49362 251 (30912) 47807 259 (29578)

Hrarr L (063)55329 224 (0000) 41015 302 (0000) 39233 310 (00000)53639 231 (0000) 32315 383 (0000) 32300 383 (00000)

8TOC

HT71723 172 (14020) 54514 227 (32032) 52971 234 (29449)

Hrarr L (064)55736 222 (16056) 43788 283 (00002) 42071 294 (00021)51485 240 (00072) 36582 338 (02814) 36469 339 (02123)

HH66172 187 (28471) 56823 218 (31391) 54455 227 (30037)

Hrarr L (064)465 55155 224 (0000) 45348 273 (0000) 43004 288 (0000)45297 273 (0000) 36233 342 (0000) 36074 343 (0000)

TT64658 191 (28253) 55533 223 (30750) 53332 232 (29676)

Hrarr L (064)53795 230 (0000) 44230 280 (00041) 42118 294 (00035)

47532 260 (0000) 35593 348(00004) 35462 349 (00001)

8TCOC

HT52952 234 (24562) 45023 275 (25260) 43961 282 (28030)

Hrarr L (062)44536 278 (00966) 38134 325 (00568) 36861 336 (00488)42203 293 (00397) 33152 373 (03015) 32230 384 (02428)

HH47208 262 (21440) 40435 306 (26989) 39618 312 (25865)

Hrarr L (062)mdash 40834 303 (00008) 35682 347 (00998) 34623 358 (00852)

39627 312 (00661) 31908 388 (02093) 28581 433 (00000)

TT46712 265 (20300) 41163 301 (27553) 39282 315 (24701)

Hrarr L (062)40397 306 (00042) 36159 342 (00509) 34187 362 (00641)39818 311 (00434) 32429 382 (03900) 31340 395 (04098)

8TOOC mdash57329 216 (26859) 48934 253 (30704) 47422 261 (29274)

Hrarr L (064)47995 258 (0000) 40835 305 (0000) 39248 315 (00001)44588 278 (0000) 34835 355 (02826) 33704 367 (02340)

The prediction of the excitation energies and oscillatorstrengths by using the CAM-B3LYP is in better agreementwith the experimental results [49 50] than is found forB3LYP because the CAM- (Coulomb-attenuating method-)B3LYP also takes account of the long-range corrections fordescribing the long 120587-conjugation [51]The results are shownin Table 4 and we note that the excitation energy values Δ119864obtained by TD-DFTCAM-B3LYP6-31G(dp) level are inagreement with those obtained by the methods DFTB3LYP6-31G(dp) level therefore theCAM-B3LYP functional is veryuseful for predicting the excitation energies and oscillatorstrengths The values calculated using the TD-DFT CAM-B3LYP function of our compounds in vacuo for predictingthe excitation energies and oscillator strengths are listed inTable 4 The TDCAM-B3LYP6-31G(dp) method was alsoemployed to simulate the optical property of the compounds

42 Effect of Solvent Solvent effects attract considerable atte-ntion because most of the chemical processes occur in thesolution phaseThe solvent effects are included here to ensure

that the calculations are compatible with the typical con-ditions The effects of chemical environment are discussedfurther as follows In order to study the effect of solvents onthe ground state molecular geometry excitation energies andmaximum absorption quantum chemical calculations on thestudied molecules were carried out in vacuum in dimethylsulfoxide (DMSO) The longest wavelength peaks from C-PCM-TD-CAM-B3LYP6-31G(dp) results are shifted com-pared to the corresponding ones using the TD-CAM-B3LYPresults The magnitudes of the spectral shifts are about 15 nmfor 8T 8TOC (HT) and 8TOOC and 1881 2201 2368 817and 1062 nm for 8TCOC (TT) 8TOC (TT) 8TOC (HH)8TCOC (HH) and 8TCOC (HT) respectively The absorp-tionmaxima of all compounds are further shifted by the effectof the dimethyl sulfoxide solventThis might be related to thegradient electrostatic potential and donor effect of the OCH

3

CH2OCH3 and OOCH

3groups Further there is a variation

of the absorption maximum displacement for the samecompound (HT TT andHH) this is the result of the differentconfigurations that one compound can take In DMSO

Journal of Chemistry 9

200 300 400 500 600 700 800 900 1000 1100

0

20000

40000

60000

80000

100000

120000

140000

8TAbEm

200 300 400 500 600 700 800 900 1000 1100

0

20000

40000

60000

80000

100000

120000

140000

8OOCAbEm

120582 (nm) 120582 (nm)

Ener

gy (a

u)

Ener

gy (a

u)

Δ120582

200 300 400 500 600 700 800 900 1000 1100

0

20000

40000

60000

80000

100000

120000

140000

AbsorptionEmission

8TCOCHHabHHemHTab

HTemTTabTTem

300 400 500 600 700 800 900 1000 1100 1200 1300

0

20000

40000

60000

80000

100000

120000Absorption Emission

8TCOHHabHHemHTab

HTemTTabTTem

120582 (nm) 120582 (nm)

Ener

gy (a

u)

Ener

gy (a

u)

Figure 7 Calculated electronic absorption and emission of octamers units of 8T 8TOC (HH HT and TT) 8TOOC and 8TCOC (HH HTand TT) obtained by CAM-B3LYP6-31G(dp)

the calculated results for the absorptionmaximumof all com-pounds are located between 56823 and 40435 nm (Table 4)The peak positions of those molecules in DMSO show a redshift when compared to those measured experimentally [26]

43 Electronic Emission Spectra TD-DFTB3LYP6-31G(dp)has been used for optimized structures and CAM-B3LYP6-31G(dp) was used to calculate the excited state and to sim-ulate the emission spectra of the considered polymers andthe first singlet excited states are listed in Table 5 Similar tothe absorption spectra 119878

1rarr 1198780fluorescence peaks in emi-

ssion spectra (Figure 6) have the greatest oscillator strengthsin all molecules and exclusively arise fromHOMOrarr LUMO(120587 rarr 120587lowast electronic transition) Polymers with aromatic orheterocyclic units generally absorb light with wavelengths in

the range from 300 to 700 nm due to 120587 rarr 120587lowast transitionsThe excited states of their chromophores (excitons) releaseenergy radiatively as well as nonradiatively on returning tothe ground state [26] The radiative decay of excitons to theground state can emit visible light These excitons are alsoformed when a bias potential is applied to an emissive poly-mer sandwiched between an anode and a cathode [52]

The theoretical studies of our molecules can be used toderive the Stokes shifts the difference between the positionof the maxima band of the absorption and emission spectrain wavelength which is about 80 to 93 nm for the structures8T 8TOC (HH TT and HT) 8TCOC (TT) and 8TOOCbut that for the 8TCOC (HH) and 8TCOC (TT) is 149 nmAmong them the compound 8TCOC has a relatively largerStokes shift which indicates that electron transitions break

10 Journal of Chemistry

Table 5 Emission spectra in gaseous phase obtained by the TD-CAM-B3LYP6-31G(d) optimized geometries of 119878

1excited states for

the octamers

Compounds 120582 (nm) 119864 (eV) OS Δ120582 = 120582ab minus 120582em55797 222 30531

8T 43390 285 00000 79836564 339 00000

8TOC

HT62147 199 29482

817646113 268 0005742181 293 02710

HH63709 196 30801

925446191 268 0000040654 304 00000

TT62147 199 29482

881546113 268 0005742181 293 02710

8TCOC

TT53079 233 26028

911840043 309 0035434914 355 03253

HH54518 247 27840

1490040748 304 0027535560 348 00001

HT56951 217 30310

1766942626 290 0000136784 337 0007956106 220 29875

8TOOC 42641 290 00002 868436421 340 00000

the strong conjugate effect leading to remarkable changes inthe structure and reorganization energy as discussed above

5 Conclusions

In this study we have used the DFTB3LYP method to inves-tigate the theoretical analysis of the geometries and electronicproperties of some type-in-derivatives structure of polythio-phene The modification of chemical structures can greatlymodify and improve the electronic and optical properties ofpristine studied materials The electronic properties of theconjugated materials based on thiophene compounds havebeen computed using the 6-31G(dp) basis set at a densityfunctional B3LYP level in order to guide the synthesis ofnovel materials with specific electronic properties

In summary the conclusions are as follows

(i) TheUV-vis absorption properties have been obtainedby using TDCAM-B3LYP and TD-B3LYP calcula-tions The obtained absorption maximums are in therange of 350ndash550 nm

(ii) The HOMO level LUMO level and band gap ofthe studied compounds were well controlled by theacceptor strength The calculated band gap (119864gap) ofthe studiedmolecules was in the range of 191ndash302 eV

(iii) The calculated values of 119881oc of the studied moleculesrange from 016 eV to 091 eVPCBM these values aresufficient for a possible efficient electron injection

The theoretical results suggest that both the donor strengthand the stable geometry contribute significantly to the elec-tronic properties of the conjugated polymers Finally the pro-cedures of theoretical calculations can be employed to predictthe electronic properties of the other compounds and furtherto design novel materials for organic solar cells

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work has been supported by the Volubilis Program(no MA11248) and the convention CNRSTCNRS (ProjectChimie 1009) The authors are grateful to the ldquoAssociationMarocaine des Chimistes Theoriciensrdquo (AMCT) for its per-tinent help Guillermo Salgado-Moran gratefully acknowl-edges Si Mohamed Bouzzine for his invitation to participatein this work Daniel Glossman-Mitnik is a researcher ofCIMAV and CONACYT and acknowledges both institutionsfor partial support

References

[1] H-J Wang C-P Chen and R-J Jeng ldquoPolythiophenes com-prising conjugated pendants for polymer solar cells a reviewrdquoMaterials vol 7 no 4 pp 2411ndash2439 2014

[2] S Pesant P Boulanger M Cote and M Ernzerhof ldquoAb initiostudy of ladder-type polymers polythiophene and polypyrrolerdquoChemical Physics Letters vol 450 no 4ndash6 pp 329ndash334 2008

[3] J Roncali ldquoConjugated poly(thiophenes) synthesis functional-ization and applicationsrdquo Chemical Reviews vol 92 no 4 pp711ndash738 1992

[4] Y Wei C-C Chan J Tian G-W Jang and K F HsuehldquoElectrochemical polymerization of thiophenes in the presenceof bithiophene or terthiophene kinetics and mechanism of thepolymerizationrdquo Chemistry of Materials vol 3 no 5 pp 888ndash897 1991

[5] R M Souto Maior K Hinkelmann H Eckert and FWudl ldquoSynthesis and characterization of two regiochemi-cally defined poly(dialkylbithiophenes) a comparative studyrdquoMacromolecules vol 23 no 5 pp 1268ndash1279 1990

[6] M-A Sato and H Morii ldquoNuclear magnetic resonance stud-ies on electrochemically prepared poly(3-dodecylthiophene)rdquoMacromolecules vol 24 no 5 pp 1196ndash1200 1991

[7] Y-J Cheng S-H Yang and C-S Hsu ldquoSynthesis of conjugatedpolymers for organic solar cell applicationsrdquo Chemical Reviewsvol 109 no 11 pp 5868ndash5923 2009

[8] A C AlgunoW C Chung R V Bantaculo et al ldquoAb initio anddensity functional studies of polythiophene energy band gaprdquoNECTEC Technical Journal vol 2 no 9 pp 215ndash218 2001

[9] J Pei W-L Yu W Huang and A J Heeger ldquoA novel series ofefficient thiophene-based light-emitting conjugated polymersand application in polymer light-emitting diodesrdquo Macro-molecules vol 33 no 7 pp 2462ndash2471 2000

Journal of Chemistry 11

[10] A K Bakhshi ldquoTheoretical tailoring of electrically conductingpolymers some new resultsrdquoMaterials Science and EngineeringC vol 3 no 3-4 pp 249ndash255 1995

[11] M S Senevirathne A Nanayakkara and G K R Senadeera ldquoAtheoretical investigation of band gaps of conducting polymersmdashpolythiophene polypyrrole and polyfuranrdquo inProceedings of the23rd Technical Sessions vol 23 pp 47ndash53 Institute of PhysicsColombo Sri Lanka March 2007

[12] U Salzner J B Lagowski P G Pickup and R A PoirierldquoDesign of low band gap polymers employing density func-tional theorymdashhybrid functionals ameliorate band gap prob-lemrdquo Journal of Computational Chemistry vol 18 no 15 pp1943ndash1953 1997

[13] E Bundgaard and F C Krebs ldquoLow band gap polymers fororganic photovoltaicsrdquo Solar Energy Materials and Solar Cellsvol 91 no 11 pp 954ndash985 2007

[14] M J Frisch G W Trucks H B Schlegel et al ldquoGaussian 09Revision B04rdquo Gaussian Inc Wallingford Conn USA 2009

[15] M E Casida C Jamorski K C Casida and D R SalahubldquoMolecular excitation energies to high-lying bound states fromtime-dependent density-functional response theory charac-terization and correction of the time-dependent local den-sity approximation ionization thresholdrdquo Journal of ChemicalPhysics vol 108 no 11 pp 4439ndash4449 1998

[16] R E Stratmann G E Scuseria and M J Frisch ldquoAn efficientimplementation of time-dependent density-functional theoryfor the calculation of excitation energies of largemoleculesrdquoTheJournal of Chemical Physics vol 109 no 19 pp 8218ndash8224 1998

[17] T Yanai D P Tew and N C Handy ldquoA new hybrid exchange-correlation functional using the Coulomb-attenuating method(CAM-B3LYP)rdquo Chemical Physics Letters vol 393 no 1ndash3 pp51ndash57 2004

[18] J Preat ldquoPhotoinduced energy-transfer and electron-transferprocesses in dye-sensitized solar cells TDDFT insights fortriphenylamine dyesrdquoThe Journal of Physical Chemistry C vol114 no 39 pp 16716ndash16725 2010

[19] B Camino M de La Pierre and A M Ferrari ldquoPhotoelectro-chemical properties of the CT1 dye a DFT studyrdquo Journal ofMolecular Structure vol 1046 pp 116ndash123 2013

[20] A Irfan R Jin A G Al-Sehemi and A M Asiri ldquoQuantumchemical study of the donor-bridge-acceptor triphenylaminebased sensitizersrdquo Spectrochimica Acta Part A Molecular andBiomolecular Spectroscopy vol 110 pp 60ndash66 2013

[21] S Jungsuttiwong R Tarsang T Sudyoadsuk V Promarak PKhongpracha and S Namuangruk ldquoTheoretical study on noveldouble donor-based dyes used in high efficient dye-sensitizedsolar cells the application of TDDFT study to the electroninjection processrdquoOrganic Electronics PhysicsMaterials Appli-cations vol 14 no 3 pp 711ndash722 2013

[22] E J Meijer D M de Leeuw S Setayesh et al ldquoSolution-processed ambipolar organic field-effect transistors and invert-ersrdquo Nature Materials vol 2 no 10 pp 678ndash682 2003

[23] V Hernandez J T L Navarrete and J L Marcos ldquoElectronicstructure and lattice dynamics of polyfuranrdquo Synthetic Metalsvol 41 no 3 pp 789ndash792 1991

[24] F B Kooistra J Knol F Kastenberg et al ldquoIncreasing the opencircuit voltage of bulk-heterojunction solar cells by raising theLUMO level of the acceptorrdquo Organic Letters vol 9 no 4 pp551ndash554 2007

[25] J J M Halls J Cornil D A dos Santos et al ldquoCharge- andenergy-transfer processes at polymerpolymer interfaces a joint

experimental and theoretical studyrdquo Physical Review B vol 60no 8 pp 5721ndash5727 1999

[26] M Fall J-J Aaron and D Gningue-Sall ldquoLuminescence prop-erties of poly(3-methoxythiophene)mdashbithiophene compositeoligomersrdquo Journal of Fluorescence vol 10 no 2 pp 107ndash1112000

[27] M Cossi N Rega G Scalmani and V Barone ldquoEnergiesstructures and electronic properties of molecules in solutionwith the C-PCM solvation modelrdquo Journal of ComputationalChemistry vol 24 no 6 pp 669ndash681 2003

[28] V Barone and M Cossi ldquoQuantum calculation of molecularenergies and energy gradients in solution by a conductor solventmodelrdquoThe Journal of Physical Chemistry A vol 102 no 11 pp1995ndash2001 1998

[29] J F Pan S J Chua and W Huang ldquoQuantum calculationof molecular energies and energy gradients in solution by aconductor solventmodelrdquoChemical Physics Letters vol 363 no1-2 pp 18ndash24 2002

[30] U Salzner J B Lagowski P G Pickup and R A Poirier ldquoCom-parison of geometries and electronic structures of polyacety-lene polyborole polycyclopentadiene polypyrrole polyfuranpolysilole polyphosphole polythiophene polyselenophene andpolytellurophenerdquo Synthetic Metals vol 96 no 3 pp 177ndash1891998

[31] A Kraak and H Wynberg ldquoCharge-transfer interaction ofdithienyls and cyclopentadithiophenes with 135-trinitroben-zene (TNB)rdquo Tetrahedron vol 24 no 10 pp 3881ndash3885 1968

[32] M Dietrich and J Heinze ldquoPoly(441015840-dimethoxybithiophe-ne)mdasha new conducting polymer with extraordinary redox andoptical propertiesrdquo SyntheticMetals vol 41 no 1-2 pp 503ndash5061991

[33] H Zgou M Hamidi M Bouachrine and K Hasnaoui ldquoTheDFT study and opto-electronic properties of copolymers basedon thiophene and phenylenerdquo Physical and Chemical News vol32 pp 81ndash87 2006

[34] L Yang J-K Feng and A-M Ren ldquoTheoretical studies onthe electronic and optical properties of two thiophene-fluorenebased 120587-conjugated copolymersrdquo Polymer vol 46 no 24 pp10970ndash10981 2005

[35] J L Bredas R Silbey D S Boudreaux and R R ChanceldquoChain-length dependence of electronic and electrochemicalproperties of conjugated systems polyacetylene polypheny-lene polythiophene and polypyrrolerdquo Journal of the AmericanChemical Society vol 105 no 22 pp 6555ndash6559 1983

[36] D Fichou G Horowitz B Xu and F Garnier ldquoStoichiometriccontrol of the successive generation of the radical cation anddication of extended 120572-conjugated oligothiophenes a quantita-tive model for doped polythiophenerdquo Synthetic Metals vol 39no 2 pp 243ndash259 1990

[37] D Fichou G Horowitz Y Nishikitani and F Garnier ldquoSemi-conducting conjugated oligomers for molecular electronicsrdquoSynthetic Metals vol 28 no 1-2 pp 723ndash727 1989

[38] V May and O Kuhn Charge and Energy Transfer Dynamics inMolecular Systems Wiley-VCH Berlin Germany 2000

[39] GDennlerMC Scharber andC J Brabec ldquoPolymer-fullerenebulk-heterojunction solar cellsrdquoAdvancedMaterials vol 21 no13 pp 1323ndash1338 2009

[40] JW Chen andY Cao ldquoDevelopment of novel conjugated donorpolymers for high-efficiency bulk-heterojunction photovoltaicdevicesrdquoAccounts of Chemical Research vol 42 no 11 pp 1709ndash1718 2009

12 Journal of Chemistry

[41] Z Cai-Rong L Zi-Jiang C Yu-Hong C Hong-Shan W You-Zhi and Y Li-Hua ldquoDFT and TDDFT study on organic dyesensitizersD5DST andDSS for solar cellsrdquo Journal ofMolecularStructure THEOCHEM vol 899 no 1ndash3 pp 86ndash93 2009

[42] Y He H-Y Chen J Hou and Y Li ldquoIndene-C60bisadduct a

new acceptor for high-performance polymer solar cellsrdquo Journalof the American Chemical Society vol 132 no 4 pp 1377ndash13822010

[43] S Gunes H Neugebauer and N S Sariciftci ldquoConjugatedpolymer-based organic solar cellsrdquo Chemical Reviews vol 107no 4 pp 1324ndash1338 2007

[44] C J Brabec A Cravino D Meissner et al ldquoOrigin of theopen circuit voltage of plastic solar cellsrdquo Advanced FuntionalMaterials vol 11 no 5 pp 374ndash380 2001

[45] M C Scharber D Muhlbacher M Koppe et al ldquoDesign rulesfor donors in bulk-heterojunction solar cellsmdashtowards 10energy-conversion efficiencyrdquo Advanced Materials vol 18 no6 pp 789ndash794 2006

[46] A Gadisa M Svensson M R Andersson and O InganasldquoCorrelation between oxidation potential and open-circuitvoltage of composite solar cells based on blends of polythio-phenesfullerene derivativerdquoApplied Physics Letters vol 84 no9 pp 1609ndash1611 2004

[47] K Kaneto K Yoshino and Y Inuishi ldquoElectrical and opticalproperties of polythiophene prepared by electrochemical poly-merizationrdquo Solid State Communications vol 46 no 5 pp 389ndash391 1983

[48] D Jacquemin J Preat V Wathelet M Fontaine and E APerpete ldquoThioindigo dyes highly accurate visible spectra withTD-DFTrdquo Journal of the American Chemical Society vol 128 no6 pp 2072ndash2083 2006

[49] N Santhanamoorthi K Senthilkumar and P KolandaivelldquoTautomerization and solvent effects on the absorption andemission properties of the Schiff base NN1015840-bis(salicylidene)-p-phenylenediaminemdasha TDDFT studyrdquoMolecular Physics vol108 no 14 pp 1817ndash1827 2010

[50] J Vasudevan R T Stibrany J Bumby et al ldquoAn edge-over-edgeZn(II) bacteriochlorin dimer having an unshifted Q

119910bandThe

importance of 120587-overlaprdquo Journal of the American ChemicalSociety vol 118 no 46 pp 11676ndash11677 1996

[51] H Scheer and H H Inhoffen ldquoHydroporphyrins reactivityspectroscopy and hydroporphyrin analoguesrdquo in The Por-phyrins DDolphin Ed vol 2 pp 45ndash90 Academic Press NewYork NY USA 1978

[52] R H Friend R W Gymer A B Holmes et al ldquoElectrolumi-nescence in conjugated polymersrdquoNature vol 397 no 6715 pp121ndash128 1999

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

6 Journal of Chemistry

HOMO LUMO

8T

8TOOC

8TOC (HT)

8TOC (TT)

8TOC (HH)

8TCOC (HT)

8TCOC (TT)

8TCOC (HH)

Figure 5 The contour plots of HOMO and LUMO orbitals of the studied compounds

33 Photovoltaic Properties Generally the most efficientpolymer solar cells are based on the bulk heterojunction(BHJ) structure of the blend of 120587-conjugated polymer donorsand fullerene derivative acceptors [7 36ndash40] Here we stud-ied the photovoltaic properties of polyalkyl thiophene with

[66]-phenyl-C61-butyric acidmethyl ester (PCBM) which isthe most widely used acceptor in solar cell devices The cor-responding structure of the photovoltaic devices is schemat-ically depicted in Figure 6 The difference in the HOMOenergy levels of 8T 8TCOC 8TOOC and the LUMO of

Journal of Chemistry 7En

ergy

(eV

)

HOMO

LUMO

minus65

minus60

minus55

minus50

minus45

minus40

minus35

minus30

minus25

minus20

minus15

PCBM

(C60

)

8TO

C (T

T)

8TO

C (H

T)

8TO

C (H

H)

8TCO

C (T

T)

8TCO

C (H

H)

8TCO

C (H

T)

8TO

OC8T

Voc

Egap

Figure 6 Band structure diagram illustrating the HOMO andLUMO energies of the studied compounds relative to the bandstructure of PCBM

PCBM was 073 eV 016 eV and 062 eV respectively butthe value of 8TOC is negative (Table 3) suggesting that thephotoexcited electron transfer from the study compounds toPCBM may be sufficiently efficient to be useful in photo-voltaic devices [24 41 42]

In principle the optimization of polymer-fullerene solarcells is based on fine-tuning the electronic properties andinteractions of the donor and acceptor components so as toabsorb themaximumquantity of light and generate the great-est number of free charges with minimal concomitant loss ofenergy and transport the charges to the electrodes Howeverit is necessary to know the ideal electronic characteristics thateach component should have for the design of the next gen-eration high-efficiency photovoltaic systems The two com-ponents required in these devices for electronic optimizationare a soluble fullerene (generally a C60 derivative) acceptorand a polymeric donor that can be processed in solutionFullerenes are currently considered to be the ideal acceptorsfor organic solar cells for several reasons First they have anenergetically deep-lying LUMO which endows the moleculewith a very high electron affinity relative to the numerouspotential organic donors [25]

It is apparent that the active layer donor-acceptor com-posite governs all aspects of the mechanism with theexception of charge collection which is based on the elec-tronic interface between the active layer composite and therespective electrode Besides the fundamental mechanisticsteps the open circuit voltage (119881oc) is also governed by theenergetic relationship between the donor and the acceptor(Figure 6) rather than the work functions of the cathode andanode as would be expected from a simplistic view of thesediode devices Specifically the energy difference between theHOMO of the donor and the LUMO of the acceptor is foundto be very closely correlated with the 119881oc value [43ndash45]

The maximum open circuit voltage (119881oc) of the BHJ solarcell is related to the difference between the highest occupiedmolecular orbital (HOMO) of the electron donor and theLUMO of the electron acceptor taking into account theenergy lost during the photocharge generation [46] The the-oretical values of open circuit voltage119881oc have been calculatedfrom the following expression

119881oc =10038161003816100381610038161003816119864HOMO

(Donor)10038161003816100381610038161003816minus

10038161003816100381610038161003816119864LUMO

(Acceptor)10038161003816100381610038161003816minus 03 (2)

Moreover these compounds have absorption maxima in theneighborhood of 400ndash540 nm (Table 4) which is the opti-mum range of absorption (UV-visible) for photovoltaic cellsIn addition they have an energy gap of the order of 200 eV(Table 3) for the elevation of the electron from the HOMO tothe LUMO orbitals This characteristic allows us to promotethese compounds for the production of solar cells Thesevalues are sufficient for a possible efficient electron injectionsystem Therefore all the studied molecules can be used asorganic solar cell components because the electron injectionprocess from the excited molecule to the conduction bandof the acceptor (PCBM) and the subsequent regeneration ispossible in photovoltaic cells

4 Optoelectronic Parameters

41 Electronic Absorption Spectra For a better understandingof the electronic properties of thiophene-based moleculesthe excitation energy based on the first and second singlet-singlet electronic transitions has been studied In recentyears time dependent density functional theory (TD-DFT)has emerged as a reliable standard tool for the theoreticaltreatment of electronic excitation spectra and recent worksdemonstrate better accuracy for a wide range of systems [4748] The TD-DFTB3LYP6-31G(dp) has been used on thebasis of the optimized geometry The nature and the energyof the singlet-singlet electronic transitions of all the oligomersin all series under study are reported in Table 4 All electronictransitions are 120587 rarr 120587lowast type and no localized electronictransitions are exhibited among the calculated singlet-singlettransition Table 4 summarizes the transition energies ofabsorption spectra and oscillator strength Two interestingtrends in oscillator strength can be found in all series ofcompounds the oscillator strength OS of 119878

0rarr 1198781is the

overwhelmingly largest of all the series of polymersAccording to Table 4 we note an excitation energy of

about 2 eV for all compounds studied In addition absorp-tion maxima were located in the 400ndash540 nm range for allcompounds indicating all molecules have only one band inthe visible region (120582abs gt 400 nm) The absorption spectra ofthese compounds showed a major absorption band assignedto the 120587 rarr 120587lowast transition local electron

According to the transition character most of the com-pounds show the HOMOrarr LUMO transition as the firstsinglet excitationThemaximum (120582max) wavelengths for UV-vis absorption spectra of all compounds simulated are shownin Figure 7 The calculated 120582max by TD-DFT-B3LY and TD-CAM-B3LYP is different by about 99 nm = 120582max(B3LYP) minus120582max(CAM-B3LYP)

8 Journal of Chemistry

Table 4 Excitation energy valuesΔ119864 for the studied compounds obtained by TD-DFTCAM-B3LYP TD-DFT B3LYPwith 6-31G (dp) level

Compounds 120582 (nm) Exp [26] TD-B3LYP TD-CAM-B3LYP (DMSO) TD-CAM-B3LYP120582 (nm) 119864 (eV) (OS) 120582 (nm) 119864 (eV) (OS) 120582 (nm) 119864 (eV) (OS) Molecular orbital

8T 44864459 192 (29063) 49362 251 (30912) 47807 259 (29578)

Hrarr L (063)55329 224 (0000) 41015 302 (0000) 39233 310 (00000)53639 231 (0000) 32315 383 (0000) 32300 383 (00000)

8TOC

HT71723 172 (14020) 54514 227 (32032) 52971 234 (29449)

Hrarr L (064)55736 222 (16056) 43788 283 (00002) 42071 294 (00021)51485 240 (00072) 36582 338 (02814) 36469 339 (02123)

HH66172 187 (28471) 56823 218 (31391) 54455 227 (30037)

Hrarr L (064)465 55155 224 (0000) 45348 273 (0000) 43004 288 (0000)45297 273 (0000) 36233 342 (0000) 36074 343 (0000)

TT64658 191 (28253) 55533 223 (30750) 53332 232 (29676)

Hrarr L (064)53795 230 (0000) 44230 280 (00041) 42118 294 (00035)

47532 260 (0000) 35593 348(00004) 35462 349 (00001)

8TCOC

HT52952 234 (24562) 45023 275 (25260) 43961 282 (28030)

Hrarr L (062)44536 278 (00966) 38134 325 (00568) 36861 336 (00488)42203 293 (00397) 33152 373 (03015) 32230 384 (02428)

HH47208 262 (21440) 40435 306 (26989) 39618 312 (25865)

Hrarr L (062)mdash 40834 303 (00008) 35682 347 (00998) 34623 358 (00852)

39627 312 (00661) 31908 388 (02093) 28581 433 (00000)

TT46712 265 (20300) 41163 301 (27553) 39282 315 (24701)

Hrarr L (062)40397 306 (00042) 36159 342 (00509) 34187 362 (00641)39818 311 (00434) 32429 382 (03900) 31340 395 (04098)

8TOOC mdash57329 216 (26859) 48934 253 (30704) 47422 261 (29274)

Hrarr L (064)47995 258 (0000) 40835 305 (0000) 39248 315 (00001)44588 278 (0000) 34835 355 (02826) 33704 367 (02340)

The prediction of the excitation energies and oscillatorstrengths by using the CAM-B3LYP is in better agreementwith the experimental results [49 50] than is found forB3LYP because the CAM- (Coulomb-attenuating method-)B3LYP also takes account of the long-range corrections fordescribing the long 120587-conjugation [51]The results are shownin Table 4 and we note that the excitation energy values Δ119864obtained by TD-DFTCAM-B3LYP6-31G(dp) level are inagreement with those obtained by the methods DFTB3LYP6-31G(dp) level therefore theCAM-B3LYP functional is veryuseful for predicting the excitation energies and oscillatorstrengths The values calculated using the TD-DFT CAM-B3LYP function of our compounds in vacuo for predictingthe excitation energies and oscillator strengths are listed inTable 4 The TDCAM-B3LYP6-31G(dp) method was alsoemployed to simulate the optical property of the compounds

42 Effect of Solvent Solvent effects attract considerable atte-ntion because most of the chemical processes occur in thesolution phaseThe solvent effects are included here to ensure

that the calculations are compatible with the typical con-ditions The effects of chemical environment are discussedfurther as follows In order to study the effect of solvents onthe ground state molecular geometry excitation energies andmaximum absorption quantum chemical calculations on thestudied molecules were carried out in vacuum in dimethylsulfoxide (DMSO) The longest wavelength peaks from C-PCM-TD-CAM-B3LYP6-31G(dp) results are shifted com-pared to the corresponding ones using the TD-CAM-B3LYPresults The magnitudes of the spectral shifts are about 15 nmfor 8T 8TOC (HT) and 8TOOC and 1881 2201 2368 817and 1062 nm for 8TCOC (TT) 8TOC (TT) 8TOC (HH)8TCOC (HH) and 8TCOC (HT) respectively The absorp-tionmaxima of all compounds are further shifted by the effectof the dimethyl sulfoxide solventThis might be related to thegradient electrostatic potential and donor effect of the OCH

3

CH2OCH3 and OOCH

3groups Further there is a variation

of the absorption maximum displacement for the samecompound (HT TT andHH) this is the result of the differentconfigurations that one compound can take In DMSO

Journal of Chemistry 9

200 300 400 500 600 700 800 900 1000 1100

0

20000

40000

60000

80000

100000

120000

140000

8TAbEm

200 300 400 500 600 700 800 900 1000 1100

0

20000

40000

60000

80000

100000

120000

140000

8OOCAbEm

120582 (nm) 120582 (nm)

Ener

gy (a

u)

Ener

gy (a

u)

Δ120582

200 300 400 500 600 700 800 900 1000 1100

0

20000

40000

60000

80000

100000

120000

140000

AbsorptionEmission

8TCOCHHabHHemHTab

HTemTTabTTem

300 400 500 600 700 800 900 1000 1100 1200 1300

0

20000

40000

60000

80000

100000

120000Absorption Emission

8TCOHHabHHemHTab

HTemTTabTTem

120582 (nm) 120582 (nm)

Ener

gy (a

u)

Ener

gy (a

u)

Figure 7 Calculated electronic absorption and emission of octamers units of 8T 8TOC (HH HT and TT) 8TOOC and 8TCOC (HH HTand TT) obtained by CAM-B3LYP6-31G(dp)

the calculated results for the absorptionmaximumof all com-pounds are located between 56823 and 40435 nm (Table 4)The peak positions of those molecules in DMSO show a redshift when compared to those measured experimentally [26]

43 Electronic Emission Spectra TD-DFTB3LYP6-31G(dp)has been used for optimized structures and CAM-B3LYP6-31G(dp) was used to calculate the excited state and to sim-ulate the emission spectra of the considered polymers andthe first singlet excited states are listed in Table 5 Similar tothe absorption spectra 119878

1rarr 1198780fluorescence peaks in emi-

ssion spectra (Figure 6) have the greatest oscillator strengthsin all molecules and exclusively arise fromHOMOrarr LUMO(120587 rarr 120587lowast electronic transition) Polymers with aromatic orheterocyclic units generally absorb light with wavelengths in

the range from 300 to 700 nm due to 120587 rarr 120587lowast transitionsThe excited states of their chromophores (excitons) releaseenergy radiatively as well as nonradiatively on returning tothe ground state [26] The radiative decay of excitons to theground state can emit visible light These excitons are alsoformed when a bias potential is applied to an emissive poly-mer sandwiched between an anode and a cathode [52]

The theoretical studies of our molecules can be used toderive the Stokes shifts the difference between the positionof the maxima band of the absorption and emission spectrain wavelength which is about 80 to 93 nm for the structures8T 8TOC (HH TT and HT) 8TCOC (TT) and 8TOOCbut that for the 8TCOC (HH) and 8TCOC (TT) is 149 nmAmong them the compound 8TCOC has a relatively largerStokes shift which indicates that electron transitions break

10 Journal of Chemistry

Table 5 Emission spectra in gaseous phase obtained by the TD-CAM-B3LYP6-31G(d) optimized geometries of 119878

1excited states for

the octamers

Compounds 120582 (nm) 119864 (eV) OS Δ120582 = 120582ab minus 120582em55797 222 30531

8T 43390 285 00000 79836564 339 00000

8TOC

HT62147 199 29482

817646113 268 0005742181 293 02710

HH63709 196 30801

925446191 268 0000040654 304 00000

TT62147 199 29482

881546113 268 0005742181 293 02710

8TCOC

TT53079 233 26028

911840043 309 0035434914 355 03253

HH54518 247 27840

1490040748 304 0027535560 348 00001

HT56951 217 30310

1766942626 290 0000136784 337 0007956106 220 29875

8TOOC 42641 290 00002 868436421 340 00000

the strong conjugate effect leading to remarkable changes inthe structure and reorganization energy as discussed above

5 Conclusions

In this study we have used the DFTB3LYP method to inves-tigate the theoretical analysis of the geometries and electronicproperties of some type-in-derivatives structure of polythio-phene The modification of chemical structures can greatlymodify and improve the electronic and optical properties ofpristine studied materials The electronic properties of theconjugated materials based on thiophene compounds havebeen computed using the 6-31G(dp) basis set at a densityfunctional B3LYP level in order to guide the synthesis ofnovel materials with specific electronic properties

In summary the conclusions are as follows

(i) TheUV-vis absorption properties have been obtainedby using TDCAM-B3LYP and TD-B3LYP calcula-tions The obtained absorption maximums are in therange of 350ndash550 nm

(ii) The HOMO level LUMO level and band gap ofthe studied compounds were well controlled by theacceptor strength The calculated band gap (119864gap) ofthe studiedmolecules was in the range of 191ndash302 eV

(iii) The calculated values of 119881oc of the studied moleculesrange from 016 eV to 091 eVPCBM these values aresufficient for a possible efficient electron injection

The theoretical results suggest that both the donor strengthand the stable geometry contribute significantly to the elec-tronic properties of the conjugated polymers Finally the pro-cedures of theoretical calculations can be employed to predictthe electronic properties of the other compounds and furtherto design novel materials for organic solar cells

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work has been supported by the Volubilis Program(no MA11248) and the convention CNRSTCNRS (ProjectChimie 1009) The authors are grateful to the ldquoAssociationMarocaine des Chimistes Theoriciensrdquo (AMCT) for its per-tinent help Guillermo Salgado-Moran gratefully acknowl-edges Si Mohamed Bouzzine for his invitation to participatein this work Daniel Glossman-Mitnik is a researcher ofCIMAV and CONACYT and acknowledges both institutionsfor partial support

References

[1] H-J Wang C-P Chen and R-J Jeng ldquoPolythiophenes com-prising conjugated pendants for polymer solar cells a reviewrdquoMaterials vol 7 no 4 pp 2411ndash2439 2014

[2] S Pesant P Boulanger M Cote and M Ernzerhof ldquoAb initiostudy of ladder-type polymers polythiophene and polypyrrolerdquoChemical Physics Letters vol 450 no 4ndash6 pp 329ndash334 2008

[3] J Roncali ldquoConjugated poly(thiophenes) synthesis functional-ization and applicationsrdquo Chemical Reviews vol 92 no 4 pp711ndash738 1992

[4] Y Wei C-C Chan J Tian G-W Jang and K F HsuehldquoElectrochemical polymerization of thiophenes in the presenceof bithiophene or terthiophene kinetics and mechanism of thepolymerizationrdquo Chemistry of Materials vol 3 no 5 pp 888ndash897 1991

[5] R M Souto Maior K Hinkelmann H Eckert and FWudl ldquoSynthesis and characterization of two regiochemi-cally defined poly(dialkylbithiophenes) a comparative studyrdquoMacromolecules vol 23 no 5 pp 1268ndash1279 1990

[6] M-A Sato and H Morii ldquoNuclear magnetic resonance stud-ies on electrochemically prepared poly(3-dodecylthiophene)rdquoMacromolecules vol 24 no 5 pp 1196ndash1200 1991

[7] Y-J Cheng S-H Yang and C-S Hsu ldquoSynthesis of conjugatedpolymers for organic solar cell applicationsrdquo Chemical Reviewsvol 109 no 11 pp 5868ndash5923 2009

[8] A C AlgunoW C Chung R V Bantaculo et al ldquoAb initio anddensity functional studies of polythiophene energy band gaprdquoNECTEC Technical Journal vol 2 no 9 pp 215ndash218 2001

[9] J Pei W-L Yu W Huang and A J Heeger ldquoA novel series ofefficient thiophene-based light-emitting conjugated polymersand application in polymer light-emitting diodesrdquo Macro-molecules vol 33 no 7 pp 2462ndash2471 2000

Journal of Chemistry 11

[10] A K Bakhshi ldquoTheoretical tailoring of electrically conductingpolymers some new resultsrdquoMaterials Science and EngineeringC vol 3 no 3-4 pp 249ndash255 1995

[11] M S Senevirathne A Nanayakkara and G K R Senadeera ldquoAtheoretical investigation of band gaps of conducting polymersmdashpolythiophene polypyrrole and polyfuranrdquo inProceedings of the23rd Technical Sessions vol 23 pp 47ndash53 Institute of PhysicsColombo Sri Lanka March 2007

[12] U Salzner J B Lagowski P G Pickup and R A PoirierldquoDesign of low band gap polymers employing density func-tional theorymdashhybrid functionals ameliorate band gap prob-lemrdquo Journal of Computational Chemistry vol 18 no 15 pp1943ndash1953 1997

[13] E Bundgaard and F C Krebs ldquoLow band gap polymers fororganic photovoltaicsrdquo Solar Energy Materials and Solar Cellsvol 91 no 11 pp 954ndash985 2007

[14] M J Frisch G W Trucks H B Schlegel et al ldquoGaussian 09Revision B04rdquo Gaussian Inc Wallingford Conn USA 2009

[15] M E Casida C Jamorski K C Casida and D R SalahubldquoMolecular excitation energies to high-lying bound states fromtime-dependent density-functional response theory charac-terization and correction of the time-dependent local den-sity approximation ionization thresholdrdquo Journal of ChemicalPhysics vol 108 no 11 pp 4439ndash4449 1998

[16] R E Stratmann G E Scuseria and M J Frisch ldquoAn efficientimplementation of time-dependent density-functional theoryfor the calculation of excitation energies of largemoleculesrdquoTheJournal of Chemical Physics vol 109 no 19 pp 8218ndash8224 1998

[17] T Yanai D P Tew and N C Handy ldquoA new hybrid exchange-correlation functional using the Coulomb-attenuating method(CAM-B3LYP)rdquo Chemical Physics Letters vol 393 no 1ndash3 pp51ndash57 2004

[18] J Preat ldquoPhotoinduced energy-transfer and electron-transferprocesses in dye-sensitized solar cells TDDFT insights fortriphenylamine dyesrdquoThe Journal of Physical Chemistry C vol114 no 39 pp 16716ndash16725 2010

[19] B Camino M de La Pierre and A M Ferrari ldquoPhotoelectro-chemical properties of the CT1 dye a DFT studyrdquo Journal ofMolecular Structure vol 1046 pp 116ndash123 2013

[20] A Irfan R Jin A G Al-Sehemi and A M Asiri ldquoQuantumchemical study of the donor-bridge-acceptor triphenylaminebased sensitizersrdquo Spectrochimica Acta Part A Molecular andBiomolecular Spectroscopy vol 110 pp 60ndash66 2013

[21] S Jungsuttiwong R Tarsang T Sudyoadsuk V Promarak PKhongpracha and S Namuangruk ldquoTheoretical study on noveldouble donor-based dyes used in high efficient dye-sensitizedsolar cells the application of TDDFT study to the electroninjection processrdquoOrganic Electronics PhysicsMaterials Appli-cations vol 14 no 3 pp 711ndash722 2013

[22] E J Meijer D M de Leeuw S Setayesh et al ldquoSolution-processed ambipolar organic field-effect transistors and invert-ersrdquo Nature Materials vol 2 no 10 pp 678ndash682 2003

[23] V Hernandez J T L Navarrete and J L Marcos ldquoElectronicstructure and lattice dynamics of polyfuranrdquo Synthetic Metalsvol 41 no 3 pp 789ndash792 1991

[24] F B Kooistra J Knol F Kastenberg et al ldquoIncreasing the opencircuit voltage of bulk-heterojunction solar cells by raising theLUMO level of the acceptorrdquo Organic Letters vol 9 no 4 pp551ndash554 2007

[25] J J M Halls J Cornil D A dos Santos et al ldquoCharge- andenergy-transfer processes at polymerpolymer interfaces a joint

experimental and theoretical studyrdquo Physical Review B vol 60no 8 pp 5721ndash5727 1999

[26] M Fall J-J Aaron and D Gningue-Sall ldquoLuminescence prop-erties of poly(3-methoxythiophene)mdashbithiophene compositeoligomersrdquo Journal of Fluorescence vol 10 no 2 pp 107ndash1112000

[27] M Cossi N Rega G Scalmani and V Barone ldquoEnergiesstructures and electronic properties of molecules in solutionwith the C-PCM solvation modelrdquo Journal of ComputationalChemistry vol 24 no 6 pp 669ndash681 2003

[28] V Barone and M Cossi ldquoQuantum calculation of molecularenergies and energy gradients in solution by a conductor solventmodelrdquoThe Journal of Physical Chemistry A vol 102 no 11 pp1995ndash2001 1998

[29] J F Pan S J Chua and W Huang ldquoQuantum calculationof molecular energies and energy gradients in solution by aconductor solventmodelrdquoChemical Physics Letters vol 363 no1-2 pp 18ndash24 2002

[30] U Salzner J B Lagowski P G Pickup and R A Poirier ldquoCom-parison of geometries and electronic structures of polyacety-lene polyborole polycyclopentadiene polypyrrole polyfuranpolysilole polyphosphole polythiophene polyselenophene andpolytellurophenerdquo Synthetic Metals vol 96 no 3 pp 177ndash1891998

[31] A Kraak and H Wynberg ldquoCharge-transfer interaction ofdithienyls and cyclopentadithiophenes with 135-trinitroben-zene (TNB)rdquo Tetrahedron vol 24 no 10 pp 3881ndash3885 1968

[32] M Dietrich and J Heinze ldquoPoly(441015840-dimethoxybithiophe-ne)mdasha new conducting polymer with extraordinary redox andoptical propertiesrdquo SyntheticMetals vol 41 no 1-2 pp 503ndash5061991

[33] H Zgou M Hamidi M Bouachrine and K Hasnaoui ldquoTheDFT study and opto-electronic properties of copolymers basedon thiophene and phenylenerdquo Physical and Chemical News vol32 pp 81ndash87 2006

[34] L Yang J-K Feng and A-M Ren ldquoTheoretical studies onthe electronic and optical properties of two thiophene-fluorenebased 120587-conjugated copolymersrdquo Polymer vol 46 no 24 pp10970ndash10981 2005

[35] J L Bredas R Silbey D S Boudreaux and R R ChanceldquoChain-length dependence of electronic and electrochemicalproperties of conjugated systems polyacetylene polypheny-lene polythiophene and polypyrrolerdquo Journal of the AmericanChemical Society vol 105 no 22 pp 6555ndash6559 1983

[36] D Fichou G Horowitz B Xu and F Garnier ldquoStoichiometriccontrol of the successive generation of the radical cation anddication of extended 120572-conjugated oligothiophenes a quantita-tive model for doped polythiophenerdquo Synthetic Metals vol 39no 2 pp 243ndash259 1990

[37] D Fichou G Horowitz Y Nishikitani and F Garnier ldquoSemi-conducting conjugated oligomers for molecular electronicsrdquoSynthetic Metals vol 28 no 1-2 pp 723ndash727 1989

[38] V May and O Kuhn Charge and Energy Transfer Dynamics inMolecular Systems Wiley-VCH Berlin Germany 2000

[39] GDennlerMC Scharber andC J Brabec ldquoPolymer-fullerenebulk-heterojunction solar cellsrdquoAdvancedMaterials vol 21 no13 pp 1323ndash1338 2009

[40] JW Chen andY Cao ldquoDevelopment of novel conjugated donorpolymers for high-efficiency bulk-heterojunction photovoltaicdevicesrdquoAccounts of Chemical Research vol 42 no 11 pp 1709ndash1718 2009

12 Journal of Chemistry

[41] Z Cai-Rong L Zi-Jiang C Yu-Hong C Hong-Shan W You-Zhi and Y Li-Hua ldquoDFT and TDDFT study on organic dyesensitizersD5DST andDSS for solar cellsrdquo Journal ofMolecularStructure THEOCHEM vol 899 no 1ndash3 pp 86ndash93 2009

[42] Y He H-Y Chen J Hou and Y Li ldquoIndene-C60bisadduct a

new acceptor for high-performance polymer solar cellsrdquo Journalof the American Chemical Society vol 132 no 4 pp 1377ndash13822010

[43] S Gunes H Neugebauer and N S Sariciftci ldquoConjugatedpolymer-based organic solar cellsrdquo Chemical Reviews vol 107no 4 pp 1324ndash1338 2007

[44] C J Brabec A Cravino D Meissner et al ldquoOrigin of theopen circuit voltage of plastic solar cellsrdquo Advanced FuntionalMaterials vol 11 no 5 pp 374ndash380 2001

[45] M C Scharber D Muhlbacher M Koppe et al ldquoDesign rulesfor donors in bulk-heterojunction solar cellsmdashtowards 10energy-conversion efficiencyrdquo Advanced Materials vol 18 no6 pp 789ndash794 2006

[46] A Gadisa M Svensson M R Andersson and O InganasldquoCorrelation between oxidation potential and open-circuitvoltage of composite solar cells based on blends of polythio-phenesfullerene derivativerdquoApplied Physics Letters vol 84 no9 pp 1609ndash1611 2004

[47] K Kaneto K Yoshino and Y Inuishi ldquoElectrical and opticalproperties of polythiophene prepared by electrochemical poly-merizationrdquo Solid State Communications vol 46 no 5 pp 389ndash391 1983

[48] D Jacquemin J Preat V Wathelet M Fontaine and E APerpete ldquoThioindigo dyes highly accurate visible spectra withTD-DFTrdquo Journal of the American Chemical Society vol 128 no6 pp 2072ndash2083 2006

[49] N Santhanamoorthi K Senthilkumar and P KolandaivelldquoTautomerization and solvent effects on the absorption andemission properties of the Schiff base NN1015840-bis(salicylidene)-p-phenylenediaminemdasha TDDFT studyrdquoMolecular Physics vol108 no 14 pp 1817ndash1827 2010

[50] J Vasudevan R T Stibrany J Bumby et al ldquoAn edge-over-edgeZn(II) bacteriochlorin dimer having an unshifted Q

119910bandThe

importance of 120587-overlaprdquo Journal of the American ChemicalSociety vol 118 no 46 pp 11676ndash11677 1996

[51] H Scheer and H H Inhoffen ldquoHydroporphyrins reactivityspectroscopy and hydroporphyrin analoguesrdquo in The Por-phyrins DDolphin Ed vol 2 pp 45ndash90 Academic Press NewYork NY USA 1978

[52] R H Friend R W Gymer A B Holmes et al ldquoElectrolumi-nescence in conjugated polymersrdquoNature vol 397 no 6715 pp121ndash128 1999

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

Journal of Chemistry 7En

ergy

(eV

)

HOMO

LUMO

minus65

minus60

minus55

minus50

minus45

minus40

minus35

minus30

minus25

minus20

minus15

PCBM

(C60

)

8TO

C (T

T)

8TO

C (H

T)

8TO

C (H

H)

8TCO

C (T

T)

8TCO

C (H

H)

8TCO

C (H

T)

8TO

OC8T

Voc

Egap

Figure 6 Band structure diagram illustrating the HOMO andLUMO energies of the studied compounds relative to the bandstructure of PCBM

PCBM was 073 eV 016 eV and 062 eV respectively butthe value of 8TOC is negative (Table 3) suggesting that thephotoexcited electron transfer from the study compounds toPCBM may be sufficiently efficient to be useful in photo-voltaic devices [24 41 42]

In principle the optimization of polymer-fullerene solarcells is based on fine-tuning the electronic properties andinteractions of the donor and acceptor components so as toabsorb themaximumquantity of light and generate the great-est number of free charges with minimal concomitant loss ofenergy and transport the charges to the electrodes Howeverit is necessary to know the ideal electronic characteristics thateach component should have for the design of the next gen-eration high-efficiency photovoltaic systems The two com-ponents required in these devices for electronic optimizationare a soluble fullerene (generally a C60 derivative) acceptorand a polymeric donor that can be processed in solutionFullerenes are currently considered to be the ideal acceptorsfor organic solar cells for several reasons First they have anenergetically deep-lying LUMO which endows the moleculewith a very high electron affinity relative to the numerouspotential organic donors [25]

It is apparent that the active layer donor-acceptor com-posite governs all aspects of the mechanism with theexception of charge collection which is based on the elec-tronic interface between the active layer composite and therespective electrode Besides the fundamental mechanisticsteps the open circuit voltage (119881oc) is also governed by theenergetic relationship between the donor and the acceptor(Figure 6) rather than the work functions of the cathode andanode as would be expected from a simplistic view of thesediode devices Specifically the energy difference between theHOMO of the donor and the LUMO of the acceptor is foundto be very closely correlated with the 119881oc value [43ndash45]

The maximum open circuit voltage (119881oc) of the BHJ solarcell is related to the difference between the highest occupiedmolecular orbital (HOMO) of the electron donor and theLUMO of the electron acceptor taking into account theenergy lost during the photocharge generation [46] The the-oretical values of open circuit voltage119881oc have been calculatedfrom the following expression

119881oc =10038161003816100381610038161003816119864HOMO

(Donor)10038161003816100381610038161003816minus

10038161003816100381610038161003816119864LUMO

(Acceptor)10038161003816100381610038161003816minus 03 (2)

Moreover these compounds have absorption maxima in theneighborhood of 400ndash540 nm (Table 4) which is the opti-mum range of absorption (UV-visible) for photovoltaic cellsIn addition they have an energy gap of the order of 200 eV(Table 3) for the elevation of the electron from the HOMO tothe LUMO orbitals This characteristic allows us to promotethese compounds for the production of solar cells Thesevalues are sufficient for a possible efficient electron injectionsystem Therefore all the studied molecules can be used asorganic solar cell components because the electron injectionprocess from the excited molecule to the conduction bandof the acceptor (PCBM) and the subsequent regeneration ispossible in photovoltaic cells

4 Optoelectronic Parameters

41 Electronic Absorption Spectra For a better understandingof the electronic properties of thiophene-based moleculesthe excitation energy based on the first and second singlet-singlet electronic transitions has been studied In recentyears time dependent density functional theory (TD-DFT)has emerged as a reliable standard tool for the theoreticaltreatment of electronic excitation spectra and recent worksdemonstrate better accuracy for a wide range of systems [4748] The TD-DFTB3LYP6-31G(dp) has been used on thebasis of the optimized geometry The nature and the energyof the singlet-singlet electronic transitions of all the oligomersin all series under study are reported in Table 4 All electronictransitions are 120587 rarr 120587lowast type and no localized electronictransitions are exhibited among the calculated singlet-singlettransition Table 4 summarizes the transition energies ofabsorption spectra and oscillator strength Two interestingtrends in oscillator strength can be found in all series ofcompounds the oscillator strength OS of 119878

0rarr 1198781is the

overwhelmingly largest of all the series of polymersAccording to Table 4 we note an excitation energy of

about 2 eV for all compounds studied In addition absorp-tion maxima were located in the 400ndash540 nm range for allcompounds indicating all molecules have only one band inthe visible region (120582abs gt 400 nm) The absorption spectra ofthese compounds showed a major absorption band assignedto the 120587 rarr 120587lowast transition local electron

According to the transition character most of the com-pounds show the HOMOrarr LUMO transition as the firstsinglet excitationThemaximum (120582max) wavelengths for UV-vis absorption spectra of all compounds simulated are shownin Figure 7 The calculated 120582max by TD-DFT-B3LY and TD-CAM-B3LYP is different by about 99 nm = 120582max(B3LYP) minus120582max(CAM-B3LYP)

8 Journal of Chemistry

Table 4 Excitation energy valuesΔ119864 for the studied compounds obtained by TD-DFTCAM-B3LYP TD-DFT B3LYPwith 6-31G (dp) level

Compounds 120582 (nm) Exp [26] TD-B3LYP TD-CAM-B3LYP (DMSO) TD-CAM-B3LYP120582 (nm) 119864 (eV) (OS) 120582 (nm) 119864 (eV) (OS) 120582 (nm) 119864 (eV) (OS) Molecular orbital

8T 44864459 192 (29063) 49362 251 (30912) 47807 259 (29578)

Hrarr L (063)55329 224 (0000) 41015 302 (0000) 39233 310 (00000)53639 231 (0000) 32315 383 (0000) 32300 383 (00000)

8TOC

HT71723 172 (14020) 54514 227 (32032) 52971 234 (29449)

Hrarr L (064)55736 222 (16056) 43788 283 (00002) 42071 294 (00021)51485 240 (00072) 36582 338 (02814) 36469 339 (02123)

HH66172 187 (28471) 56823 218 (31391) 54455 227 (30037)

Hrarr L (064)465 55155 224 (0000) 45348 273 (0000) 43004 288 (0000)45297 273 (0000) 36233 342 (0000) 36074 343 (0000)

TT64658 191 (28253) 55533 223 (30750) 53332 232 (29676)

Hrarr L (064)53795 230 (0000) 44230 280 (00041) 42118 294 (00035)

47532 260 (0000) 35593 348(00004) 35462 349 (00001)

8TCOC

HT52952 234 (24562) 45023 275 (25260) 43961 282 (28030)

Hrarr L (062)44536 278 (00966) 38134 325 (00568) 36861 336 (00488)42203 293 (00397) 33152 373 (03015) 32230 384 (02428)

HH47208 262 (21440) 40435 306 (26989) 39618 312 (25865)

Hrarr L (062)mdash 40834 303 (00008) 35682 347 (00998) 34623 358 (00852)

39627 312 (00661) 31908 388 (02093) 28581 433 (00000)

TT46712 265 (20300) 41163 301 (27553) 39282 315 (24701)

Hrarr L (062)40397 306 (00042) 36159 342 (00509) 34187 362 (00641)39818 311 (00434) 32429 382 (03900) 31340 395 (04098)

8TOOC mdash57329 216 (26859) 48934 253 (30704) 47422 261 (29274)

Hrarr L (064)47995 258 (0000) 40835 305 (0000) 39248 315 (00001)44588 278 (0000) 34835 355 (02826) 33704 367 (02340)

The prediction of the excitation energies and oscillatorstrengths by using the CAM-B3LYP is in better agreementwith the experimental results [49 50] than is found forB3LYP because the CAM- (Coulomb-attenuating method-)B3LYP also takes account of the long-range corrections fordescribing the long 120587-conjugation [51]The results are shownin Table 4 and we note that the excitation energy values Δ119864obtained by TD-DFTCAM-B3LYP6-31G(dp) level are inagreement with those obtained by the methods DFTB3LYP6-31G(dp) level therefore theCAM-B3LYP functional is veryuseful for predicting the excitation energies and oscillatorstrengths The values calculated using the TD-DFT CAM-B3LYP function of our compounds in vacuo for predictingthe excitation energies and oscillator strengths are listed inTable 4 The TDCAM-B3LYP6-31G(dp) method was alsoemployed to simulate the optical property of the compounds

42 Effect of Solvent Solvent effects attract considerable atte-ntion because most of the chemical processes occur in thesolution phaseThe solvent effects are included here to ensure

that the calculations are compatible with the typical con-ditions The effects of chemical environment are discussedfurther as follows In order to study the effect of solvents onthe ground state molecular geometry excitation energies andmaximum absorption quantum chemical calculations on thestudied molecules were carried out in vacuum in dimethylsulfoxide (DMSO) The longest wavelength peaks from C-PCM-TD-CAM-B3LYP6-31G(dp) results are shifted com-pared to the corresponding ones using the TD-CAM-B3LYPresults The magnitudes of the spectral shifts are about 15 nmfor 8T 8TOC (HT) and 8TOOC and 1881 2201 2368 817and 1062 nm for 8TCOC (TT) 8TOC (TT) 8TOC (HH)8TCOC (HH) and 8TCOC (HT) respectively The absorp-tionmaxima of all compounds are further shifted by the effectof the dimethyl sulfoxide solventThis might be related to thegradient electrostatic potential and donor effect of the OCH

3

CH2OCH3 and OOCH

3groups Further there is a variation

of the absorption maximum displacement for the samecompound (HT TT andHH) this is the result of the differentconfigurations that one compound can take In DMSO

Journal of Chemistry 9

200 300 400 500 600 700 800 900 1000 1100

0

20000

40000

60000

80000

100000

120000

140000

8TAbEm

200 300 400 500 600 700 800 900 1000 1100

0

20000

40000

60000

80000

100000

120000

140000

8OOCAbEm

120582 (nm) 120582 (nm)

Ener

gy (a

u)

Ener

gy (a

u)

Δ120582

200 300 400 500 600 700 800 900 1000 1100

0

20000

40000

60000

80000

100000

120000

140000

AbsorptionEmission

8TCOCHHabHHemHTab

HTemTTabTTem

300 400 500 600 700 800 900 1000 1100 1200 1300

0

20000

40000

60000

80000

100000

120000Absorption Emission

8TCOHHabHHemHTab

HTemTTabTTem

120582 (nm) 120582 (nm)

Ener

gy (a

u)

Ener

gy (a

u)

Figure 7 Calculated electronic absorption and emission of octamers units of 8T 8TOC (HH HT and TT) 8TOOC and 8TCOC (HH HTand TT) obtained by CAM-B3LYP6-31G(dp)

the calculated results for the absorptionmaximumof all com-pounds are located between 56823 and 40435 nm (Table 4)The peak positions of those molecules in DMSO show a redshift when compared to those measured experimentally [26]

43 Electronic Emission Spectra TD-DFTB3LYP6-31G(dp)has been used for optimized structures and CAM-B3LYP6-31G(dp) was used to calculate the excited state and to sim-ulate the emission spectra of the considered polymers andthe first singlet excited states are listed in Table 5 Similar tothe absorption spectra 119878

1rarr 1198780fluorescence peaks in emi-

ssion spectra (Figure 6) have the greatest oscillator strengthsin all molecules and exclusively arise fromHOMOrarr LUMO(120587 rarr 120587lowast electronic transition) Polymers with aromatic orheterocyclic units generally absorb light with wavelengths in

the range from 300 to 700 nm due to 120587 rarr 120587lowast transitionsThe excited states of their chromophores (excitons) releaseenergy radiatively as well as nonradiatively on returning tothe ground state [26] The radiative decay of excitons to theground state can emit visible light These excitons are alsoformed when a bias potential is applied to an emissive poly-mer sandwiched between an anode and a cathode [52]

The theoretical studies of our molecules can be used toderive the Stokes shifts the difference between the positionof the maxima band of the absorption and emission spectrain wavelength which is about 80 to 93 nm for the structures8T 8TOC (HH TT and HT) 8TCOC (TT) and 8TOOCbut that for the 8TCOC (HH) and 8TCOC (TT) is 149 nmAmong them the compound 8TCOC has a relatively largerStokes shift which indicates that electron transitions break

10 Journal of Chemistry

Table 5 Emission spectra in gaseous phase obtained by the TD-CAM-B3LYP6-31G(d) optimized geometries of 119878

1excited states for

the octamers

Compounds 120582 (nm) 119864 (eV) OS Δ120582 = 120582ab minus 120582em55797 222 30531

8T 43390 285 00000 79836564 339 00000

8TOC

HT62147 199 29482

817646113 268 0005742181 293 02710

HH63709 196 30801

925446191 268 0000040654 304 00000

TT62147 199 29482

881546113 268 0005742181 293 02710

8TCOC

TT53079 233 26028

911840043 309 0035434914 355 03253

HH54518 247 27840

1490040748 304 0027535560 348 00001

HT56951 217 30310

1766942626 290 0000136784 337 0007956106 220 29875

8TOOC 42641 290 00002 868436421 340 00000

the strong conjugate effect leading to remarkable changes inthe structure and reorganization energy as discussed above

5 Conclusions

In this study we have used the DFTB3LYP method to inves-tigate the theoretical analysis of the geometries and electronicproperties of some type-in-derivatives structure of polythio-phene The modification of chemical structures can greatlymodify and improve the electronic and optical properties ofpristine studied materials The electronic properties of theconjugated materials based on thiophene compounds havebeen computed using the 6-31G(dp) basis set at a densityfunctional B3LYP level in order to guide the synthesis ofnovel materials with specific electronic properties

In summary the conclusions are as follows

(i) TheUV-vis absorption properties have been obtainedby using TDCAM-B3LYP and TD-B3LYP calcula-tions The obtained absorption maximums are in therange of 350ndash550 nm

(ii) The HOMO level LUMO level and band gap ofthe studied compounds were well controlled by theacceptor strength The calculated band gap (119864gap) ofthe studiedmolecules was in the range of 191ndash302 eV

(iii) The calculated values of 119881oc of the studied moleculesrange from 016 eV to 091 eVPCBM these values aresufficient for a possible efficient electron injection

The theoretical results suggest that both the donor strengthand the stable geometry contribute significantly to the elec-tronic properties of the conjugated polymers Finally the pro-cedures of theoretical calculations can be employed to predictthe electronic properties of the other compounds and furtherto design novel materials for organic solar cells

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work has been supported by the Volubilis Program(no MA11248) and the convention CNRSTCNRS (ProjectChimie 1009) The authors are grateful to the ldquoAssociationMarocaine des Chimistes Theoriciensrdquo (AMCT) for its per-tinent help Guillermo Salgado-Moran gratefully acknowl-edges Si Mohamed Bouzzine for his invitation to participatein this work Daniel Glossman-Mitnik is a researcher ofCIMAV and CONACYT and acknowledges both institutionsfor partial support

References

[1] H-J Wang C-P Chen and R-J Jeng ldquoPolythiophenes com-prising conjugated pendants for polymer solar cells a reviewrdquoMaterials vol 7 no 4 pp 2411ndash2439 2014

[2] S Pesant P Boulanger M Cote and M Ernzerhof ldquoAb initiostudy of ladder-type polymers polythiophene and polypyrrolerdquoChemical Physics Letters vol 450 no 4ndash6 pp 329ndash334 2008

[3] J Roncali ldquoConjugated poly(thiophenes) synthesis functional-ization and applicationsrdquo Chemical Reviews vol 92 no 4 pp711ndash738 1992

[4] Y Wei C-C Chan J Tian G-W Jang and K F HsuehldquoElectrochemical polymerization of thiophenes in the presenceof bithiophene or terthiophene kinetics and mechanism of thepolymerizationrdquo Chemistry of Materials vol 3 no 5 pp 888ndash897 1991

[5] R M Souto Maior K Hinkelmann H Eckert and FWudl ldquoSynthesis and characterization of two regiochemi-cally defined poly(dialkylbithiophenes) a comparative studyrdquoMacromolecules vol 23 no 5 pp 1268ndash1279 1990

[6] M-A Sato and H Morii ldquoNuclear magnetic resonance stud-ies on electrochemically prepared poly(3-dodecylthiophene)rdquoMacromolecules vol 24 no 5 pp 1196ndash1200 1991

[7] Y-J Cheng S-H Yang and C-S Hsu ldquoSynthesis of conjugatedpolymers for organic solar cell applicationsrdquo Chemical Reviewsvol 109 no 11 pp 5868ndash5923 2009

[8] A C AlgunoW C Chung R V Bantaculo et al ldquoAb initio anddensity functional studies of polythiophene energy band gaprdquoNECTEC Technical Journal vol 2 no 9 pp 215ndash218 2001

[9] J Pei W-L Yu W Huang and A J Heeger ldquoA novel series ofefficient thiophene-based light-emitting conjugated polymersand application in polymer light-emitting diodesrdquo Macro-molecules vol 33 no 7 pp 2462ndash2471 2000

Journal of Chemistry 11

[10] A K Bakhshi ldquoTheoretical tailoring of electrically conductingpolymers some new resultsrdquoMaterials Science and EngineeringC vol 3 no 3-4 pp 249ndash255 1995

[11] M S Senevirathne A Nanayakkara and G K R Senadeera ldquoAtheoretical investigation of band gaps of conducting polymersmdashpolythiophene polypyrrole and polyfuranrdquo inProceedings of the23rd Technical Sessions vol 23 pp 47ndash53 Institute of PhysicsColombo Sri Lanka March 2007

[12] U Salzner J B Lagowski P G Pickup and R A PoirierldquoDesign of low band gap polymers employing density func-tional theorymdashhybrid functionals ameliorate band gap prob-lemrdquo Journal of Computational Chemistry vol 18 no 15 pp1943ndash1953 1997

[13] E Bundgaard and F C Krebs ldquoLow band gap polymers fororganic photovoltaicsrdquo Solar Energy Materials and Solar Cellsvol 91 no 11 pp 954ndash985 2007

[14] M J Frisch G W Trucks H B Schlegel et al ldquoGaussian 09Revision B04rdquo Gaussian Inc Wallingford Conn USA 2009

[15] M E Casida C Jamorski K C Casida and D R SalahubldquoMolecular excitation energies to high-lying bound states fromtime-dependent density-functional response theory charac-terization and correction of the time-dependent local den-sity approximation ionization thresholdrdquo Journal of ChemicalPhysics vol 108 no 11 pp 4439ndash4449 1998

[16] R E Stratmann G E Scuseria and M J Frisch ldquoAn efficientimplementation of time-dependent density-functional theoryfor the calculation of excitation energies of largemoleculesrdquoTheJournal of Chemical Physics vol 109 no 19 pp 8218ndash8224 1998

[17] T Yanai D P Tew and N C Handy ldquoA new hybrid exchange-correlation functional using the Coulomb-attenuating method(CAM-B3LYP)rdquo Chemical Physics Letters vol 393 no 1ndash3 pp51ndash57 2004

[18] J Preat ldquoPhotoinduced energy-transfer and electron-transferprocesses in dye-sensitized solar cells TDDFT insights fortriphenylamine dyesrdquoThe Journal of Physical Chemistry C vol114 no 39 pp 16716ndash16725 2010

[19] B Camino M de La Pierre and A M Ferrari ldquoPhotoelectro-chemical properties of the CT1 dye a DFT studyrdquo Journal ofMolecular Structure vol 1046 pp 116ndash123 2013

[20] A Irfan R Jin A G Al-Sehemi and A M Asiri ldquoQuantumchemical study of the donor-bridge-acceptor triphenylaminebased sensitizersrdquo Spectrochimica Acta Part A Molecular andBiomolecular Spectroscopy vol 110 pp 60ndash66 2013

[21] S Jungsuttiwong R Tarsang T Sudyoadsuk V Promarak PKhongpracha and S Namuangruk ldquoTheoretical study on noveldouble donor-based dyes used in high efficient dye-sensitizedsolar cells the application of TDDFT study to the electroninjection processrdquoOrganic Electronics PhysicsMaterials Appli-cations vol 14 no 3 pp 711ndash722 2013

[22] E J Meijer D M de Leeuw S Setayesh et al ldquoSolution-processed ambipolar organic field-effect transistors and invert-ersrdquo Nature Materials vol 2 no 10 pp 678ndash682 2003

[23] V Hernandez J T L Navarrete and J L Marcos ldquoElectronicstructure and lattice dynamics of polyfuranrdquo Synthetic Metalsvol 41 no 3 pp 789ndash792 1991

[24] F B Kooistra J Knol F Kastenberg et al ldquoIncreasing the opencircuit voltage of bulk-heterojunction solar cells by raising theLUMO level of the acceptorrdquo Organic Letters vol 9 no 4 pp551ndash554 2007

[25] J J M Halls J Cornil D A dos Santos et al ldquoCharge- andenergy-transfer processes at polymerpolymer interfaces a joint

experimental and theoretical studyrdquo Physical Review B vol 60no 8 pp 5721ndash5727 1999

[26] M Fall J-J Aaron and D Gningue-Sall ldquoLuminescence prop-erties of poly(3-methoxythiophene)mdashbithiophene compositeoligomersrdquo Journal of Fluorescence vol 10 no 2 pp 107ndash1112000

[27] M Cossi N Rega G Scalmani and V Barone ldquoEnergiesstructures and electronic properties of molecules in solutionwith the C-PCM solvation modelrdquo Journal of ComputationalChemistry vol 24 no 6 pp 669ndash681 2003

[28] V Barone and M Cossi ldquoQuantum calculation of molecularenergies and energy gradients in solution by a conductor solventmodelrdquoThe Journal of Physical Chemistry A vol 102 no 11 pp1995ndash2001 1998

[29] J F Pan S J Chua and W Huang ldquoQuantum calculationof molecular energies and energy gradients in solution by aconductor solventmodelrdquoChemical Physics Letters vol 363 no1-2 pp 18ndash24 2002

[30] U Salzner J B Lagowski P G Pickup and R A Poirier ldquoCom-parison of geometries and electronic structures of polyacety-lene polyborole polycyclopentadiene polypyrrole polyfuranpolysilole polyphosphole polythiophene polyselenophene andpolytellurophenerdquo Synthetic Metals vol 96 no 3 pp 177ndash1891998

[31] A Kraak and H Wynberg ldquoCharge-transfer interaction ofdithienyls and cyclopentadithiophenes with 135-trinitroben-zene (TNB)rdquo Tetrahedron vol 24 no 10 pp 3881ndash3885 1968

[32] M Dietrich and J Heinze ldquoPoly(441015840-dimethoxybithiophe-ne)mdasha new conducting polymer with extraordinary redox andoptical propertiesrdquo SyntheticMetals vol 41 no 1-2 pp 503ndash5061991

[33] H Zgou M Hamidi M Bouachrine and K Hasnaoui ldquoTheDFT study and opto-electronic properties of copolymers basedon thiophene and phenylenerdquo Physical and Chemical News vol32 pp 81ndash87 2006

[34] L Yang J-K Feng and A-M Ren ldquoTheoretical studies onthe electronic and optical properties of two thiophene-fluorenebased 120587-conjugated copolymersrdquo Polymer vol 46 no 24 pp10970ndash10981 2005

[35] J L Bredas R Silbey D S Boudreaux and R R ChanceldquoChain-length dependence of electronic and electrochemicalproperties of conjugated systems polyacetylene polypheny-lene polythiophene and polypyrrolerdquo Journal of the AmericanChemical Society vol 105 no 22 pp 6555ndash6559 1983

[36] D Fichou G Horowitz B Xu and F Garnier ldquoStoichiometriccontrol of the successive generation of the radical cation anddication of extended 120572-conjugated oligothiophenes a quantita-tive model for doped polythiophenerdquo Synthetic Metals vol 39no 2 pp 243ndash259 1990

[37] D Fichou G Horowitz Y Nishikitani and F Garnier ldquoSemi-conducting conjugated oligomers for molecular electronicsrdquoSynthetic Metals vol 28 no 1-2 pp 723ndash727 1989

[38] V May and O Kuhn Charge and Energy Transfer Dynamics inMolecular Systems Wiley-VCH Berlin Germany 2000

[39] GDennlerMC Scharber andC J Brabec ldquoPolymer-fullerenebulk-heterojunction solar cellsrdquoAdvancedMaterials vol 21 no13 pp 1323ndash1338 2009

[40] JW Chen andY Cao ldquoDevelopment of novel conjugated donorpolymers for high-efficiency bulk-heterojunction photovoltaicdevicesrdquoAccounts of Chemical Research vol 42 no 11 pp 1709ndash1718 2009

12 Journal of Chemistry

[41] Z Cai-Rong L Zi-Jiang C Yu-Hong C Hong-Shan W You-Zhi and Y Li-Hua ldquoDFT and TDDFT study on organic dyesensitizersD5DST andDSS for solar cellsrdquo Journal ofMolecularStructure THEOCHEM vol 899 no 1ndash3 pp 86ndash93 2009

[42] Y He H-Y Chen J Hou and Y Li ldquoIndene-C60bisadduct a

new acceptor for high-performance polymer solar cellsrdquo Journalof the American Chemical Society vol 132 no 4 pp 1377ndash13822010

[43] S Gunes H Neugebauer and N S Sariciftci ldquoConjugatedpolymer-based organic solar cellsrdquo Chemical Reviews vol 107no 4 pp 1324ndash1338 2007

[44] C J Brabec A Cravino D Meissner et al ldquoOrigin of theopen circuit voltage of plastic solar cellsrdquo Advanced FuntionalMaterials vol 11 no 5 pp 374ndash380 2001

[45] M C Scharber D Muhlbacher M Koppe et al ldquoDesign rulesfor donors in bulk-heterojunction solar cellsmdashtowards 10energy-conversion efficiencyrdquo Advanced Materials vol 18 no6 pp 789ndash794 2006

[46] A Gadisa M Svensson M R Andersson and O InganasldquoCorrelation between oxidation potential and open-circuitvoltage of composite solar cells based on blends of polythio-phenesfullerene derivativerdquoApplied Physics Letters vol 84 no9 pp 1609ndash1611 2004

[47] K Kaneto K Yoshino and Y Inuishi ldquoElectrical and opticalproperties of polythiophene prepared by electrochemical poly-merizationrdquo Solid State Communications vol 46 no 5 pp 389ndash391 1983

[48] D Jacquemin J Preat V Wathelet M Fontaine and E APerpete ldquoThioindigo dyes highly accurate visible spectra withTD-DFTrdquo Journal of the American Chemical Society vol 128 no6 pp 2072ndash2083 2006

[49] N Santhanamoorthi K Senthilkumar and P KolandaivelldquoTautomerization and solvent effects on the absorption andemission properties of the Schiff base NN1015840-bis(salicylidene)-p-phenylenediaminemdasha TDDFT studyrdquoMolecular Physics vol108 no 14 pp 1817ndash1827 2010

[50] J Vasudevan R T Stibrany J Bumby et al ldquoAn edge-over-edgeZn(II) bacteriochlorin dimer having an unshifted Q

119910bandThe

importance of 120587-overlaprdquo Journal of the American ChemicalSociety vol 118 no 46 pp 11676ndash11677 1996

[51] H Scheer and H H Inhoffen ldquoHydroporphyrins reactivityspectroscopy and hydroporphyrin analoguesrdquo in The Por-phyrins DDolphin Ed vol 2 pp 45ndash90 Academic Press NewYork NY USA 1978

[52] R H Friend R W Gymer A B Holmes et al ldquoElectrolumi-nescence in conjugated polymersrdquoNature vol 397 no 6715 pp121ndash128 1999

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

8 Journal of Chemistry

Table 4 Excitation energy valuesΔ119864 for the studied compounds obtained by TD-DFTCAM-B3LYP TD-DFT B3LYPwith 6-31G (dp) level

Compounds 120582 (nm) Exp [26] TD-B3LYP TD-CAM-B3LYP (DMSO) TD-CAM-B3LYP120582 (nm) 119864 (eV) (OS) 120582 (nm) 119864 (eV) (OS) 120582 (nm) 119864 (eV) (OS) Molecular orbital

8T 44864459 192 (29063) 49362 251 (30912) 47807 259 (29578)

Hrarr L (063)55329 224 (0000) 41015 302 (0000) 39233 310 (00000)53639 231 (0000) 32315 383 (0000) 32300 383 (00000)

8TOC

HT71723 172 (14020) 54514 227 (32032) 52971 234 (29449)

Hrarr L (064)55736 222 (16056) 43788 283 (00002) 42071 294 (00021)51485 240 (00072) 36582 338 (02814) 36469 339 (02123)

HH66172 187 (28471) 56823 218 (31391) 54455 227 (30037)

Hrarr L (064)465 55155 224 (0000) 45348 273 (0000) 43004 288 (0000)45297 273 (0000) 36233 342 (0000) 36074 343 (0000)

TT64658 191 (28253) 55533 223 (30750) 53332 232 (29676)

Hrarr L (064)53795 230 (0000) 44230 280 (00041) 42118 294 (00035)

47532 260 (0000) 35593 348(00004) 35462 349 (00001)

8TCOC

HT52952 234 (24562) 45023 275 (25260) 43961 282 (28030)

Hrarr L (062)44536 278 (00966) 38134 325 (00568) 36861 336 (00488)42203 293 (00397) 33152 373 (03015) 32230 384 (02428)

HH47208 262 (21440) 40435 306 (26989) 39618 312 (25865)

Hrarr L (062)mdash 40834 303 (00008) 35682 347 (00998) 34623 358 (00852)

39627 312 (00661) 31908 388 (02093) 28581 433 (00000)

TT46712 265 (20300) 41163 301 (27553) 39282 315 (24701)

Hrarr L (062)40397 306 (00042) 36159 342 (00509) 34187 362 (00641)39818 311 (00434) 32429 382 (03900) 31340 395 (04098)

8TOOC mdash57329 216 (26859) 48934 253 (30704) 47422 261 (29274)

Hrarr L (064)47995 258 (0000) 40835 305 (0000) 39248 315 (00001)44588 278 (0000) 34835 355 (02826) 33704 367 (02340)

The prediction of the excitation energies and oscillatorstrengths by using the CAM-B3LYP is in better agreementwith the experimental results [49 50] than is found forB3LYP because the CAM- (Coulomb-attenuating method-)B3LYP also takes account of the long-range corrections fordescribing the long 120587-conjugation [51]The results are shownin Table 4 and we note that the excitation energy values Δ119864obtained by TD-DFTCAM-B3LYP6-31G(dp) level are inagreement with those obtained by the methods DFTB3LYP6-31G(dp) level therefore theCAM-B3LYP functional is veryuseful for predicting the excitation energies and oscillatorstrengths The values calculated using the TD-DFT CAM-B3LYP function of our compounds in vacuo for predictingthe excitation energies and oscillator strengths are listed inTable 4 The TDCAM-B3LYP6-31G(dp) method was alsoemployed to simulate the optical property of the compounds

42 Effect of Solvent Solvent effects attract considerable atte-ntion because most of the chemical processes occur in thesolution phaseThe solvent effects are included here to ensure

that the calculations are compatible with the typical con-ditions The effects of chemical environment are discussedfurther as follows In order to study the effect of solvents onthe ground state molecular geometry excitation energies andmaximum absorption quantum chemical calculations on thestudied molecules were carried out in vacuum in dimethylsulfoxide (DMSO) The longest wavelength peaks from C-PCM-TD-CAM-B3LYP6-31G(dp) results are shifted com-pared to the corresponding ones using the TD-CAM-B3LYPresults The magnitudes of the spectral shifts are about 15 nmfor 8T 8TOC (HT) and 8TOOC and 1881 2201 2368 817and 1062 nm for 8TCOC (TT) 8TOC (TT) 8TOC (HH)8TCOC (HH) and 8TCOC (HT) respectively The absorp-tionmaxima of all compounds are further shifted by the effectof the dimethyl sulfoxide solventThis might be related to thegradient electrostatic potential and donor effect of the OCH

3

CH2OCH3 and OOCH

3groups Further there is a variation

of the absorption maximum displacement for the samecompound (HT TT andHH) this is the result of the differentconfigurations that one compound can take In DMSO

Journal of Chemistry 9

200 300 400 500 600 700 800 900 1000 1100

0

20000

40000

60000

80000

100000

120000

140000

8TAbEm

200 300 400 500 600 700 800 900 1000 1100

0

20000

40000

60000

80000

100000

120000

140000

8OOCAbEm

120582 (nm) 120582 (nm)

Ener

gy (a

u)

Ener

gy (a

u)

Δ120582

200 300 400 500 600 700 800 900 1000 1100

0

20000

40000

60000

80000

100000

120000

140000

AbsorptionEmission

8TCOCHHabHHemHTab

HTemTTabTTem

300 400 500 600 700 800 900 1000 1100 1200 1300

0

20000

40000

60000

80000

100000

120000Absorption Emission

8TCOHHabHHemHTab

HTemTTabTTem

120582 (nm) 120582 (nm)

Ener

gy (a

u)

Ener

gy (a

u)

Figure 7 Calculated electronic absorption and emission of octamers units of 8T 8TOC (HH HT and TT) 8TOOC and 8TCOC (HH HTand TT) obtained by CAM-B3LYP6-31G(dp)

the calculated results for the absorptionmaximumof all com-pounds are located between 56823 and 40435 nm (Table 4)The peak positions of those molecules in DMSO show a redshift when compared to those measured experimentally [26]

43 Electronic Emission Spectra TD-DFTB3LYP6-31G(dp)has been used for optimized structures and CAM-B3LYP6-31G(dp) was used to calculate the excited state and to sim-ulate the emission spectra of the considered polymers andthe first singlet excited states are listed in Table 5 Similar tothe absorption spectra 119878

1rarr 1198780fluorescence peaks in emi-

ssion spectra (Figure 6) have the greatest oscillator strengthsin all molecules and exclusively arise fromHOMOrarr LUMO(120587 rarr 120587lowast electronic transition) Polymers with aromatic orheterocyclic units generally absorb light with wavelengths in

the range from 300 to 700 nm due to 120587 rarr 120587lowast transitionsThe excited states of their chromophores (excitons) releaseenergy radiatively as well as nonradiatively on returning tothe ground state [26] The radiative decay of excitons to theground state can emit visible light These excitons are alsoformed when a bias potential is applied to an emissive poly-mer sandwiched between an anode and a cathode [52]

The theoretical studies of our molecules can be used toderive the Stokes shifts the difference between the positionof the maxima band of the absorption and emission spectrain wavelength which is about 80 to 93 nm for the structures8T 8TOC (HH TT and HT) 8TCOC (TT) and 8TOOCbut that for the 8TCOC (HH) and 8TCOC (TT) is 149 nmAmong them the compound 8TCOC has a relatively largerStokes shift which indicates that electron transitions break

10 Journal of Chemistry

Table 5 Emission spectra in gaseous phase obtained by the TD-CAM-B3LYP6-31G(d) optimized geometries of 119878

1excited states for

the octamers

Compounds 120582 (nm) 119864 (eV) OS Δ120582 = 120582ab minus 120582em55797 222 30531

8T 43390 285 00000 79836564 339 00000

8TOC

HT62147 199 29482

817646113 268 0005742181 293 02710

HH63709 196 30801

925446191 268 0000040654 304 00000

TT62147 199 29482

881546113 268 0005742181 293 02710

8TCOC

TT53079 233 26028

911840043 309 0035434914 355 03253

HH54518 247 27840

1490040748 304 0027535560 348 00001

HT56951 217 30310

1766942626 290 0000136784 337 0007956106 220 29875

8TOOC 42641 290 00002 868436421 340 00000

the strong conjugate effect leading to remarkable changes inthe structure and reorganization energy as discussed above

5 Conclusions

In this study we have used the DFTB3LYP method to inves-tigate the theoretical analysis of the geometries and electronicproperties of some type-in-derivatives structure of polythio-phene The modification of chemical structures can greatlymodify and improve the electronic and optical properties ofpristine studied materials The electronic properties of theconjugated materials based on thiophene compounds havebeen computed using the 6-31G(dp) basis set at a densityfunctional B3LYP level in order to guide the synthesis ofnovel materials with specific electronic properties

In summary the conclusions are as follows

(i) TheUV-vis absorption properties have been obtainedby using TDCAM-B3LYP and TD-B3LYP calcula-tions The obtained absorption maximums are in therange of 350ndash550 nm

(ii) The HOMO level LUMO level and band gap ofthe studied compounds were well controlled by theacceptor strength The calculated band gap (119864gap) ofthe studiedmolecules was in the range of 191ndash302 eV

(iii) The calculated values of 119881oc of the studied moleculesrange from 016 eV to 091 eVPCBM these values aresufficient for a possible efficient electron injection

The theoretical results suggest that both the donor strengthand the stable geometry contribute significantly to the elec-tronic properties of the conjugated polymers Finally the pro-cedures of theoretical calculations can be employed to predictthe electronic properties of the other compounds and furtherto design novel materials for organic solar cells

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work has been supported by the Volubilis Program(no MA11248) and the convention CNRSTCNRS (ProjectChimie 1009) The authors are grateful to the ldquoAssociationMarocaine des Chimistes Theoriciensrdquo (AMCT) for its per-tinent help Guillermo Salgado-Moran gratefully acknowl-edges Si Mohamed Bouzzine for his invitation to participatein this work Daniel Glossman-Mitnik is a researcher ofCIMAV and CONACYT and acknowledges both institutionsfor partial support

References

[1] H-J Wang C-P Chen and R-J Jeng ldquoPolythiophenes com-prising conjugated pendants for polymer solar cells a reviewrdquoMaterials vol 7 no 4 pp 2411ndash2439 2014

[2] S Pesant P Boulanger M Cote and M Ernzerhof ldquoAb initiostudy of ladder-type polymers polythiophene and polypyrrolerdquoChemical Physics Letters vol 450 no 4ndash6 pp 329ndash334 2008

[3] J Roncali ldquoConjugated poly(thiophenes) synthesis functional-ization and applicationsrdquo Chemical Reviews vol 92 no 4 pp711ndash738 1992

[4] Y Wei C-C Chan J Tian G-W Jang and K F HsuehldquoElectrochemical polymerization of thiophenes in the presenceof bithiophene or terthiophene kinetics and mechanism of thepolymerizationrdquo Chemistry of Materials vol 3 no 5 pp 888ndash897 1991

[5] R M Souto Maior K Hinkelmann H Eckert and FWudl ldquoSynthesis and characterization of two regiochemi-cally defined poly(dialkylbithiophenes) a comparative studyrdquoMacromolecules vol 23 no 5 pp 1268ndash1279 1990

[6] M-A Sato and H Morii ldquoNuclear magnetic resonance stud-ies on electrochemically prepared poly(3-dodecylthiophene)rdquoMacromolecules vol 24 no 5 pp 1196ndash1200 1991

[7] Y-J Cheng S-H Yang and C-S Hsu ldquoSynthesis of conjugatedpolymers for organic solar cell applicationsrdquo Chemical Reviewsvol 109 no 11 pp 5868ndash5923 2009

[8] A C AlgunoW C Chung R V Bantaculo et al ldquoAb initio anddensity functional studies of polythiophene energy band gaprdquoNECTEC Technical Journal vol 2 no 9 pp 215ndash218 2001

[9] J Pei W-L Yu W Huang and A J Heeger ldquoA novel series ofefficient thiophene-based light-emitting conjugated polymersand application in polymer light-emitting diodesrdquo Macro-molecules vol 33 no 7 pp 2462ndash2471 2000

Journal of Chemistry 11

[10] A K Bakhshi ldquoTheoretical tailoring of electrically conductingpolymers some new resultsrdquoMaterials Science and EngineeringC vol 3 no 3-4 pp 249ndash255 1995

[11] M S Senevirathne A Nanayakkara and G K R Senadeera ldquoAtheoretical investigation of band gaps of conducting polymersmdashpolythiophene polypyrrole and polyfuranrdquo inProceedings of the23rd Technical Sessions vol 23 pp 47ndash53 Institute of PhysicsColombo Sri Lanka March 2007

[12] U Salzner J B Lagowski P G Pickup and R A PoirierldquoDesign of low band gap polymers employing density func-tional theorymdashhybrid functionals ameliorate band gap prob-lemrdquo Journal of Computational Chemistry vol 18 no 15 pp1943ndash1953 1997

[13] E Bundgaard and F C Krebs ldquoLow band gap polymers fororganic photovoltaicsrdquo Solar Energy Materials and Solar Cellsvol 91 no 11 pp 954ndash985 2007

[14] M J Frisch G W Trucks H B Schlegel et al ldquoGaussian 09Revision B04rdquo Gaussian Inc Wallingford Conn USA 2009

[15] M E Casida C Jamorski K C Casida and D R SalahubldquoMolecular excitation energies to high-lying bound states fromtime-dependent density-functional response theory charac-terization and correction of the time-dependent local den-sity approximation ionization thresholdrdquo Journal of ChemicalPhysics vol 108 no 11 pp 4439ndash4449 1998

[16] R E Stratmann G E Scuseria and M J Frisch ldquoAn efficientimplementation of time-dependent density-functional theoryfor the calculation of excitation energies of largemoleculesrdquoTheJournal of Chemical Physics vol 109 no 19 pp 8218ndash8224 1998

[17] T Yanai D P Tew and N C Handy ldquoA new hybrid exchange-correlation functional using the Coulomb-attenuating method(CAM-B3LYP)rdquo Chemical Physics Letters vol 393 no 1ndash3 pp51ndash57 2004

[18] J Preat ldquoPhotoinduced energy-transfer and electron-transferprocesses in dye-sensitized solar cells TDDFT insights fortriphenylamine dyesrdquoThe Journal of Physical Chemistry C vol114 no 39 pp 16716ndash16725 2010

[19] B Camino M de La Pierre and A M Ferrari ldquoPhotoelectro-chemical properties of the CT1 dye a DFT studyrdquo Journal ofMolecular Structure vol 1046 pp 116ndash123 2013

[20] A Irfan R Jin A G Al-Sehemi and A M Asiri ldquoQuantumchemical study of the donor-bridge-acceptor triphenylaminebased sensitizersrdquo Spectrochimica Acta Part A Molecular andBiomolecular Spectroscopy vol 110 pp 60ndash66 2013

[21] S Jungsuttiwong R Tarsang T Sudyoadsuk V Promarak PKhongpracha and S Namuangruk ldquoTheoretical study on noveldouble donor-based dyes used in high efficient dye-sensitizedsolar cells the application of TDDFT study to the electroninjection processrdquoOrganic Electronics PhysicsMaterials Appli-cations vol 14 no 3 pp 711ndash722 2013

[22] E J Meijer D M de Leeuw S Setayesh et al ldquoSolution-processed ambipolar organic field-effect transistors and invert-ersrdquo Nature Materials vol 2 no 10 pp 678ndash682 2003

[23] V Hernandez J T L Navarrete and J L Marcos ldquoElectronicstructure and lattice dynamics of polyfuranrdquo Synthetic Metalsvol 41 no 3 pp 789ndash792 1991

[24] F B Kooistra J Knol F Kastenberg et al ldquoIncreasing the opencircuit voltage of bulk-heterojunction solar cells by raising theLUMO level of the acceptorrdquo Organic Letters vol 9 no 4 pp551ndash554 2007

[25] J J M Halls J Cornil D A dos Santos et al ldquoCharge- andenergy-transfer processes at polymerpolymer interfaces a joint

experimental and theoretical studyrdquo Physical Review B vol 60no 8 pp 5721ndash5727 1999

[26] M Fall J-J Aaron and D Gningue-Sall ldquoLuminescence prop-erties of poly(3-methoxythiophene)mdashbithiophene compositeoligomersrdquo Journal of Fluorescence vol 10 no 2 pp 107ndash1112000

[27] M Cossi N Rega G Scalmani and V Barone ldquoEnergiesstructures and electronic properties of molecules in solutionwith the C-PCM solvation modelrdquo Journal of ComputationalChemistry vol 24 no 6 pp 669ndash681 2003

[28] V Barone and M Cossi ldquoQuantum calculation of molecularenergies and energy gradients in solution by a conductor solventmodelrdquoThe Journal of Physical Chemistry A vol 102 no 11 pp1995ndash2001 1998

[29] J F Pan S J Chua and W Huang ldquoQuantum calculationof molecular energies and energy gradients in solution by aconductor solventmodelrdquoChemical Physics Letters vol 363 no1-2 pp 18ndash24 2002

[30] U Salzner J B Lagowski P G Pickup and R A Poirier ldquoCom-parison of geometries and electronic structures of polyacety-lene polyborole polycyclopentadiene polypyrrole polyfuranpolysilole polyphosphole polythiophene polyselenophene andpolytellurophenerdquo Synthetic Metals vol 96 no 3 pp 177ndash1891998

[31] A Kraak and H Wynberg ldquoCharge-transfer interaction ofdithienyls and cyclopentadithiophenes with 135-trinitroben-zene (TNB)rdquo Tetrahedron vol 24 no 10 pp 3881ndash3885 1968

[32] M Dietrich and J Heinze ldquoPoly(441015840-dimethoxybithiophe-ne)mdasha new conducting polymer with extraordinary redox andoptical propertiesrdquo SyntheticMetals vol 41 no 1-2 pp 503ndash5061991

[33] H Zgou M Hamidi M Bouachrine and K Hasnaoui ldquoTheDFT study and opto-electronic properties of copolymers basedon thiophene and phenylenerdquo Physical and Chemical News vol32 pp 81ndash87 2006

[34] L Yang J-K Feng and A-M Ren ldquoTheoretical studies onthe electronic and optical properties of two thiophene-fluorenebased 120587-conjugated copolymersrdquo Polymer vol 46 no 24 pp10970ndash10981 2005

[35] J L Bredas R Silbey D S Boudreaux and R R ChanceldquoChain-length dependence of electronic and electrochemicalproperties of conjugated systems polyacetylene polypheny-lene polythiophene and polypyrrolerdquo Journal of the AmericanChemical Society vol 105 no 22 pp 6555ndash6559 1983

[36] D Fichou G Horowitz B Xu and F Garnier ldquoStoichiometriccontrol of the successive generation of the radical cation anddication of extended 120572-conjugated oligothiophenes a quantita-tive model for doped polythiophenerdquo Synthetic Metals vol 39no 2 pp 243ndash259 1990

[37] D Fichou G Horowitz Y Nishikitani and F Garnier ldquoSemi-conducting conjugated oligomers for molecular electronicsrdquoSynthetic Metals vol 28 no 1-2 pp 723ndash727 1989

[38] V May and O Kuhn Charge and Energy Transfer Dynamics inMolecular Systems Wiley-VCH Berlin Germany 2000

[39] GDennlerMC Scharber andC J Brabec ldquoPolymer-fullerenebulk-heterojunction solar cellsrdquoAdvancedMaterials vol 21 no13 pp 1323ndash1338 2009

[40] JW Chen andY Cao ldquoDevelopment of novel conjugated donorpolymers for high-efficiency bulk-heterojunction photovoltaicdevicesrdquoAccounts of Chemical Research vol 42 no 11 pp 1709ndash1718 2009

12 Journal of Chemistry

[41] Z Cai-Rong L Zi-Jiang C Yu-Hong C Hong-Shan W You-Zhi and Y Li-Hua ldquoDFT and TDDFT study on organic dyesensitizersD5DST andDSS for solar cellsrdquo Journal ofMolecularStructure THEOCHEM vol 899 no 1ndash3 pp 86ndash93 2009

[42] Y He H-Y Chen J Hou and Y Li ldquoIndene-C60bisadduct a

new acceptor for high-performance polymer solar cellsrdquo Journalof the American Chemical Society vol 132 no 4 pp 1377ndash13822010

[43] S Gunes H Neugebauer and N S Sariciftci ldquoConjugatedpolymer-based organic solar cellsrdquo Chemical Reviews vol 107no 4 pp 1324ndash1338 2007

[44] C J Brabec A Cravino D Meissner et al ldquoOrigin of theopen circuit voltage of plastic solar cellsrdquo Advanced FuntionalMaterials vol 11 no 5 pp 374ndash380 2001

[45] M C Scharber D Muhlbacher M Koppe et al ldquoDesign rulesfor donors in bulk-heterojunction solar cellsmdashtowards 10energy-conversion efficiencyrdquo Advanced Materials vol 18 no6 pp 789ndash794 2006

[46] A Gadisa M Svensson M R Andersson and O InganasldquoCorrelation between oxidation potential and open-circuitvoltage of composite solar cells based on blends of polythio-phenesfullerene derivativerdquoApplied Physics Letters vol 84 no9 pp 1609ndash1611 2004

[47] K Kaneto K Yoshino and Y Inuishi ldquoElectrical and opticalproperties of polythiophene prepared by electrochemical poly-merizationrdquo Solid State Communications vol 46 no 5 pp 389ndash391 1983

[48] D Jacquemin J Preat V Wathelet M Fontaine and E APerpete ldquoThioindigo dyes highly accurate visible spectra withTD-DFTrdquo Journal of the American Chemical Society vol 128 no6 pp 2072ndash2083 2006

[49] N Santhanamoorthi K Senthilkumar and P KolandaivelldquoTautomerization and solvent effects on the absorption andemission properties of the Schiff base NN1015840-bis(salicylidene)-p-phenylenediaminemdasha TDDFT studyrdquoMolecular Physics vol108 no 14 pp 1817ndash1827 2010

[50] J Vasudevan R T Stibrany J Bumby et al ldquoAn edge-over-edgeZn(II) bacteriochlorin dimer having an unshifted Q

119910bandThe

importance of 120587-overlaprdquo Journal of the American ChemicalSociety vol 118 no 46 pp 11676ndash11677 1996

[51] H Scheer and H H Inhoffen ldquoHydroporphyrins reactivityspectroscopy and hydroporphyrin analoguesrdquo in The Por-phyrins DDolphin Ed vol 2 pp 45ndash90 Academic Press NewYork NY USA 1978

[52] R H Friend R W Gymer A B Holmes et al ldquoElectrolumi-nescence in conjugated polymersrdquoNature vol 397 no 6715 pp121ndash128 1999

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

Journal of Chemistry 9

200 300 400 500 600 700 800 900 1000 1100

0

20000

40000

60000

80000

100000

120000

140000

8TAbEm

200 300 400 500 600 700 800 900 1000 1100

0

20000

40000

60000

80000

100000

120000

140000

8OOCAbEm

120582 (nm) 120582 (nm)

Ener

gy (a

u)

Ener

gy (a

u)

Δ120582

200 300 400 500 600 700 800 900 1000 1100

0

20000

40000

60000

80000

100000

120000

140000

AbsorptionEmission

8TCOCHHabHHemHTab

HTemTTabTTem

300 400 500 600 700 800 900 1000 1100 1200 1300

0

20000

40000

60000

80000

100000

120000Absorption Emission

8TCOHHabHHemHTab

HTemTTabTTem

120582 (nm) 120582 (nm)

Ener

gy (a

u)

Ener

gy (a

u)

Figure 7 Calculated electronic absorption and emission of octamers units of 8T 8TOC (HH HT and TT) 8TOOC and 8TCOC (HH HTand TT) obtained by CAM-B3LYP6-31G(dp)

the calculated results for the absorptionmaximumof all com-pounds are located between 56823 and 40435 nm (Table 4)The peak positions of those molecules in DMSO show a redshift when compared to those measured experimentally [26]

43 Electronic Emission Spectra TD-DFTB3LYP6-31G(dp)has been used for optimized structures and CAM-B3LYP6-31G(dp) was used to calculate the excited state and to sim-ulate the emission spectra of the considered polymers andthe first singlet excited states are listed in Table 5 Similar tothe absorption spectra 119878

1rarr 1198780fluorescence peaks in emi-

ssion spectra (Figure 6) have the greatest oscillator strengthsin all molecules and exclusively arise fromHOMOrarr LUMO(120587 rarr 120587lowast electronic transition) Polymers with aromatic orheterocyclic units generally absorb light with wavelengths in

the range from 300 to 700 nm due to 120587 rarr 120587lowast transitionsThe excited states of their chromophores (excitons) releaseenergy radiatively as well as nonradiatively on returning tothe ground state [26] The radiative decay of excitons to theground state can emit visible light These excitons are alsoformed when a bias potential is applied to an emissive poly-mer sandwiched between an anode and a cathode [52]

The theoretical studies of our molecules can be used toderive the Stokes shifts the difference between the positionof the maxima band of the absorption and emission spectrain wavelength which is about 80 to 93 nm for the structures8T 8TOC (HH TT and HT) 8TCOC (TT) and 8TOOCbut that for the 8TCOC (HH) and 8TCOC (TT) is 149 nmAmong them the compound 8TCOC has a relatively largerStokes shift which indicates that electron transitions break

10 Journal of Chemistry

Table 5 Emission spectra in gaseous phase obtained by the TD-CAM-B3LYP6-31G(d) optimized geometries of 119878

1excited states for

the octamers

Compounds 120582 (nm) 119864 (eV) OS Δ120582 = 120582ab minus 120582em55797 222 30531

8T 43390 285 00000 79836564 339 00000

8TOC

HT62147 199 29482

817646113 268 0005742181 293 02710

HH63709 196 30801

925446191 268 0000040654 304 00000

TT62147 199 29482

881546113 268 0005742181 293 02710

8TCOC

TT53079 233 26028

911840043 309 0035434914 355 03253

HH54518 247 27840

1490040748 304 0027535560 348 00001

HT56951 217 30310

1766942626 290 0000136784 337 0007956106 220 29875

8TOOC 42641 290 00002 868436421 340 00000

the strong conjugate effect leading to remarkable changes inthe structure and reorganization energy as discussed above

5 Conclusions

In this study we have used the DFTB3LYP method to inves-tigate the theoretical analysis of the geometries and electronicproperties of some type-in-derivatives structure of polythio-phene The modification of chemical structures can greatlymodify and improve the electronic and optical properties ofpristine studied materials The electronic properties of theconjugated materials based on thiophene compounds havebeen computed using the 6-31G(dp) basis set at a densityfunctional B3LYP level in order to guide the synthesis ofnovel materials with specific electronic properties

In summary the conclusions are as follows

(i) TheUV-vis absorption properties have been obtainedby using TDCAM-B3LYP and TD-B3LYP calcula-tions The obtained absorption maximums are in therange of 350ndash550 nm

(ii) The HOMO level LUMO level and band gap ofthe studied compounds were well controlled by theacceptor strength The calculated band gap (119864gap) ofthe studiedmolecules was in the range of 191ndash302 eV

(iii) The calculated values of 119881oc of the studied moleculesrange from 016 eV to 091 eVPCBM these values aresufficient for a possible efficient electron injection

The theoretical results suggest that both the donor strengthand the stable geometry contribute significantly to the elec-tronic properties of the conjugated polymers Finally the pro-cedures of theoretical calculations can be employed to predictthe electronic properties of the other compounds and furtherto design novel materials for organic solar cells

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work has been supported by the Volubilis Program(no MA11248) and the convention CNRSTCNRS (ProjectChimie 1009) The authors are grateful to the ldquoAssociationMarocaine des Chimistes Theoriciensrdquo (AMCT) for its per-tinent help Guillermo Salgado-Moran gratefully acknowl-edges Si Mohamed Bouzzine for his invitation to participatein this work Daniel Glossman-Mitnik is a researcher ofCIMAV and CONACYT and acknowledges both institutionsfor partial support

References

[1] H-J Wang C-P Chen and R-J Jeng ldquoPolythiophenes com-prising conjugated pendants for polymer solar cells a reviewrdquoMaterials vol 7 no 4 pp 2411ndash2439 2014

[2] S Pesant P Boulanger M Cote and M Ernzerhof ldquoAb initiostudy of ladder-type polymers polythiophene and polypyrrolerdquoChemical Physics Letters vol 450 no 4ndash6 pp 329ndash334 2008

[3] J Roncali ldquoConjugated poly(thiophenes) synthesis functional-ization and applicationsrdquo Chemical Reviews vol 92 no 4 pp711ndash738 1992

[4] Y Wei C-C Chan J Tian G-W Jang and K F HsuehldquoElectrochemical polymerization of thiophenes in the presenceof bithiophene or terthiophene kinetics and mechanism of thepolymerizationrdquo Chemistry of Materials vol 3 no 5 pp 888ndash897 1991

[5] R M Souto Maior K Hinkelmann H Eckert and FWudl ldquoSynthesis and characterization of two regiochemi-cally defined poly(dialkylbithiophenes) a comparative studyrdquoMacromolecules vol 23 no 5 pp 1268ndash1279 1990

[6] M-A Sato and H Morii ldquoNuclear magnetic resonance stud-ies on electrochemically prepared poly(3-dodecylthiophene)rdquoMacromolecules vol 24 no 5 pp 1196ndash1200 1991

[7] Y-J Cheng S-H Yang and C-S Hsu ldquoSynthesis of conjugatedpolymers for organic solar cell applicationsrdquo Chemical Reviewsvol 109 no 11 pp 5868ndash5923 2009

[8] A C AlgunoW C Chung R V Bantaculo et al ldquoAb initio anddensity functional studies of polythiophene energy band gaprdquoNECTEC Technical Journal vol 2 no 9 pp 215ndash218 2001

[9] J Pei W-L Yu W Huang and A J Heeger ldquoA novel series ofefficient thiophene-based light-emitting conjugated polymersand application in polymer light-emitting diodesrdquo Macro-molecules vol 33 no 7 pp 2462ndash2471 2000

Journal of Chemistry 11

[10] A K Bakhshi ldquoTheoretical tailoring of electrically conductingpolymers some new resultsrdquoMaterials Science and EngineeringC vol 3 no 3-4 pp 249ndash255 1995

[11] M S Senevirathne A Nanayakkara and G K R Senadeera ldquoAtheoretical investigation of band gaps of conducting polymersmdashpolythiophene polypyrrole and polyfuranrdquo inProceedings of the23rd Technical Sessions vol 23 pp 47ndash53 Institute of PhysicsColombo Sri Lanka March 2007

[12] U Salzner J B Lagowski P G Pickup and R A PoirierldquoDesign of low band gap polymers employing density func-tional theorymdashhybrid functionals ameliorate band gap prob-lemrdquo Journal of Computational Chemistry vol 18 no 15 pp1943ndash1953 1997

[13] E Bundgaard and F C Krebs ldquoLow band gap polymers fororganic photovoltaicsrdquo Solar Energy Materials and Solar Cellsvol 91 no 11 pp 954ndash985 2007

[14] M J Frisch G W Trucks H B Schlegel et al ldquoGaussian 09Revision B04rdquo Gaussian Inc Wallingford Conn USA 2009

[15] M E Casida C Jamorski K C Casida and D R SalahubldquoMolecular excitation energies to high-lying bound states fromtime-dependent density-functional response theory charac-terization and correction of the time-dependent local den-sity approximation ionization thresholdrdquo Journal of ChemicalPhysics vol 108 no 11 pp 4439ndash4449 1998

[16] R E Stratmann G E Scuseria and M J Frisch ldquoAn efficientimplementation of time-dependent density-functional theoryfor the calculation of excitation energies of largemoleculesrdquoTheJournal of Chemical Physics vol 109 no 19 pp 8218ndash8224 1998

[17] T Yanai D P Tew and N C Handy ldquoA new hybrid exchange-correlation functional using the Coulomb-attenuating method(CAM-B3LYP)rdquo Chemical Physics Letters vol 393 no 1ndash3 pp51ndash57 2004

[18] J Preat ldquoPhotoinduced energy-transfer and electron-transferprocesses in dye-sensitized solar cells TDDFT insights fortriphenylamine dyesrdquoThe Journal of Physical Chemistry C vol114 no 39 pp 16716ndash16725 2010

[19] B Camino M de La Pierre and A M Ferrari ldquoPhotoelectro-chemical properties of the CT1 dye a DFT studyrdquo Journal ofMolecular Structure vol 1046 pp 116ndash123 2013

[20] A Irfan R Jin A G Al-Sehemi and A M Asiri ldquoQuantumchemical study of the donor-bridge-acceptor triphenylaminebased sensitizersrdquo Spectrochimica Acta Part A Molecular andBiomolecular Spectroscopy vol 110 pp 60ndash66 2013

[21] S Jungsuttiwong R Tarsang T Sudyoadsuk V Promarak PKhongpracha and S Namuangruk ldquoTheoretical study on noveldouble donor-based dyes used in high efficient dye-sensitizedsolar cells the application of TDDFT study to the electroninjection processrdquoOrganic Electronics PhysicsMaterials Appli-cations vol 14 no 3 pp 711ndash722 2013

[22] E J Meijer D M de Leeuw S Setayesh et al ldquoSolution-processed ambipolar organic field-effect transistors and invert-ersrdquo Nature Materials vol 2 no 10 pp 678ndash682 2003

[23] V Hernandez J T L Navarrete and J L Marcos ldquoElectronicstructure and lattice dynamics of polyfuranrdquo Synthetic Metalsvol 41 no 3 pp 789ndash792 1991

[24] F B Kooistra J Knol F Kastenberg et al ldquoIncreasing the opencircuit voltage of bulk-heterojunction solar cells by raising theLUMO level of the acceptorrdquo Organic Letters vol 9 no 4 pp551ndash554 2007

[25] J J M Halls J Cornil D A dos Santos et al ldquoCharge- andenergy-transfer processes at polymerpolymer interfaces a joint

experimental and theoretical studyrdquo Physical Review B vol 60no 8 pp 5721ndash5727 1999

[26] M Fall J-J Aaron and D Gningue-Sall ldquoLuminescence prop-erties of poly(3-methoxythiophene)mdashbithiophene compositeoligomersrdquo Journal of Fluorescence vol 10 no 2 pp 107ndash1112000

[27] M Cossi N Rega G Scalmani and V Barone ldquoEnergiesstructures and electronic properties of molecules in solutionwith the C-PCM solvation modelrdquo Journal of ComputationalChemistry vol 24 no 6 pp 669ndash681 2003

[28] V Barone and M Cossi ldquoQuantum calculation of molecularenergies and energy gradients in solution by a conductor solventmodelrdquoThe Journal of Physical Chemistry A vol 102 no 11 pp1995ndash2001 1998

[29] J F Pan S J Chua and W Huang ldquoQuantum calculationof molecular energies and energy gradients in solution by aconductor solventmodelrdquoChemical Physics Letters vol 363 no1-2 pp 18ndash24 2002

[30] U Salzner J B Lagowski P G Pickup and R A Poirier ldquoCom-parison of geometries and electronic structures of polyacety-lene polyborole polycyclopentadiene polypyrrole polyfuranpolysilole polyphosphole polythiophene polyselenophene andpolytellurophenerdquo Synthetic Metals vol 96 no 3 pp 177ndash1891998

[31] A Kraak and H Wynberg ldquoCharge-transfer interaction ofdithienyls and cyclopentadithiophenes with 135-trinitroben-zene (TNB)rdquo Tetrahedron vol 24 no 10 pp 3881ndash3885 1968

[32] M Dietrich and J Heinze ldquoPoly(441015840-dimethoxybithiophe-ne)mdasha new conducting polymer with extraordinary redox andoptical propertiesrdquo SyntheticMetals vol 41 no 1-2 pp 503ndash5061991

[33] H Zgou M Hamidi M Bouachrine and K Hasnaoui ldquoTheDFT study and opto-electronic properties of copolymers basedon thiophene and phenylenerdquo Physical and Chemical News vol32 pp 81ndash87 2006

[34] L Yang J-K Feng and A-M Ren ldquoTheoretical studies onthe electronic and optical properties of two thiophene-fluorenebased 120587-conjugated copolymersrdquo Polymer vol 46 no 24 pp10970ndash10981 2005

[35] J L Bredas R Silbey D S Boudreaux and R R ChanceldquoChain-length dependence of electronic and electrochemicalproperties of conjugated systems polyacetylene polypheny-lene polythiophene and polypyrrolerdquo Journal of the AmericanChemical Society vol 105 no 22 pp 6555ndash6559 1983

[36] D Fichou G Horowitz B Xu and F Garnier ldquoStoichiometriccontrol of the successive generation of the radical cation anddication of extended 120572-conjugated oligothiophenes a quantita-tive model for doped polythiophenerdquo Synthetic Metals vol 39no 2 pp 243ndash259 1990

[37] D Fichou G Horowitz Y Nishikitani and F Garnier ldquoSemi-conducting conjugated oligomers for molecular electronicsrdquoSynthetic Metals vol 28 no 1-2 pp 723ndash727 1989

[38] V May and O Kuhn Charge and Energy Transfer Dynamics inMolecular Systems Wiley-VCH Berlin Germany 2000

[39] GDennlerMC Scharber andC J Brabec ldquoPolymer-fullerenebulk-heterojunction solar cellsrdquoAdvancedMaterials vol 21 no13 pp 1323ndash1338 2009

[40] JW Chen andY Cao ldquoDevelopment of novel conjugated donorpolymers for high-efficiency bulk-heterojunction photovoltaicdevicesrdquoAccounts of Chemical Research vol 42 no 11 pp 1709ndash1718 2009

12 Journal of Chemistry

[41] Z Cai-Rong L Zi-Jiang C Yu-Hong C Hong-Shan W You-Zhi and Y Li-Hua ldquoDFT and TDDFT study on organic dyesensitizersD5DST andDSS for solar cellsrdquo Journal ofMolecularStructure THEOCHEM vol 899 no 1ndash3 pp 86ndash93 2009

[42] Y He H-Y Chen J Hou and Y Li ldquoIndene-C60bisadduct a

new acceptor for high-performance polymer solar cellsrdquo Journalof the American Chemical Society vol 132 no 4 pp 1377ndash13822010

[43] S Gunes H Neugebauer and N S Sariciftci ldquoConjugatedpolymer-based organic solar cellsrdquo Chemical Reviews vol 107no 4 pp 1324ndash1338 2007

[44] C J Brabec A Cravino D Meissner et al ldquoOrigin of theopen circuit voltage of plastic solar cellsrdquo Advanced FuntionalMaterials vol 11 no 5 pp 374ndash380 2001

[45] M C Scharber D Muhlbacher M Koppe et al ldquoDesign rulesfor donors in bulk-heterojunction solar cellsmdashtowards 10energy-conversion efficiencyrdquo Advanced Materials vol 18 no6 pp 789ndash794 2006

[46] A Gadisa M Svensson M R Andersson and O InganasldquoCorrelation between oxidation potential and open-circuitvoltage of composite solar cells based on blends of polythio-phenesfullerene derivativerdquoApplied Physics Letters vol 84 no9 pp 1609ndash1611 2004

[47] K Kaneto K Yoshino and Y Inuishi ldquoElectrical and opticalproperties of polythiophene prepared by electrochemical poly-merizationrdquo Solid State Communications vol 46 no 5 pp 389ndash391 1983

[48] D Jacquemin J Preat V Wathelet M Fontaine and E APerpete ldquoThioindigo dyes highly accurate visible spectra withTD-DFTrdquo Journal of the American Chemical Society vol 128 no6 pp 2072ndash2083 2006

[49] N Santhanamoorthi K Senthilkumar and P KolandaivelldquoTautomerization and solvent effects on the absorption andemission properties of the Schiff base NN1015840-bis(salicylidene)-p-phenylenediaminemdasha TDDFT studyrdquoMolecular Physics vol108 no 14 pp 1817ndash1827 2010

[50] J Vasudevan R T Stibrany J Bumby et al ldquoAn edge-over-edgeZn(II) bacteriochlorin dimer having an unshifted Q

119910bandThe

importance of 120587-overlaprdquo Journal of the American ChemicalSociety vol 118 no 46 pp 11676ndash11677 1996

[51] H Scheer and H H Inhoffen ldquoHydroporphyrins reactivityspectroscopy and hydroporphyrin analoguesrdquo in The Por-phyrins DDolphin Ed vol 2 pp 45ndash90 Academic Press NewYork NY USA 1978

[52] R H Friend R W Gymer A B Holmes et al ldquoElectrolumi-nescence in conjugated polymersrdquoNature vol 397 no 6715 pp121ndash128 1999

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

10 Journal of Chemistry

Table 5 Emission spectra in gaseous phase obtained by the TD-CAM-B3LYP6-31G(d) optimized geometries of 119878

1excited states for

the octamers

Compounds 120582 (nm) 119864 (eV) OS Δ120582 = 120582ab minus 120582em55797 222 30531

8T 43390 285 00000 79836564 339 00000

8TOC

HT62147 199 29482

817646113 268 0005742181 293 02710

HH63709 196 30801

925446191 268 0000040654 304 00000

TT62147 199 29482

881546113 268 0005742181 293 02710

8TCOC

TT53079 233 26028

911840043 309 0035434914 355 03253

HH54518 247 27840

1490040748 304 0027535560 348 00001

HT56951 217 30310

1766942626 290 0000136784 337 0007956106 220 29875

8TOOC 42641 290 00002 868436421 340 00000

the strong conjugate effect leading to remarkable changes inthe structure and reorganization energy as discussed above

5 Conclusions

In this study we have used the DFTB3LYP method to inves-tigate the theoretical analysis of the geometries and electronicproperties of some type-in-derivatives structure of polythio-phene The modification of chemical structures can greatlymodify and improve the electronic and optical properties ofpristine studied materials The electronic properties of theconjugated materials based on thiophene compounds havebeen computed using the 6-31G(dp) basis set at a densityfunctional B3LYP level in order to guide the synthesis ofnovel materials with specific electronic properties

In summary the conclusions are as follows

(i) TheUV-vis absorption properties have been obtainedby using TDCAM-B3LYP and TD-B3LYP calcula-tions The obtained absorption maximums are in therange of 350ndash550 nm

(ii) The HOMO level LUMO level and band gap ofthe studied compounds were well controlled by theacceptor strength The calculated band gap (119864gap) ofthe studiedmolecules was in the range of 191ndash302 eV

(iii) The calculated values of 119881oc of the studied moleculesrange from 016 eV to 091 eVPCBM these values aresufficient for a possible efficient electron injection

The theoretical results suggest that both the donor strengthand the stable geometry contribute significantly to the elec-tronic properties of the conjugated polymers Finally the pro-cedures of theoretical calculations can be employed to predictthe electronic properties of the other compounds and furtherto design novel materials for organic solar cells

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work has been supported by the Volubilis Program(no MA11248) and the convention CNRSTCNRS (ProjectChimie 1009) The authors are grateful to the ldquoAssociationMarocaine des Chimistes Theoriciensrdquo (AMCT) for its per-tinent help Guillermo Salgado-Moran gratefully acknowl-edges Si Mohamed Bouzzine for his invitation to participatein this work Daniel Glossman-Mitnik is a researcher ofCIMAV and CONACYT and acknowledges both institutionsfor partial support

References

[1] H-J Wang C-P Chen and R-J Jeng ldquoPolythiophenes com-prising conjugated pendants for polymer solar cells a reviewrdquoMaterials vol 7 no 4 pp 2411ndash2439 2014

[2] S Pesant P Boulanger M Cote and M Ernzerhof ldquoAb initiostudy of ladder-type polymers polythiophene and polypyrrolerdquoChemical Physics Letters vol 450 no 4ndash6 pp 329ndash334 2008

[3] J Roncali ldquoConjugated poly(thiophenes) synthesis functional-ization and applicationsrdquo Chemical Reviews vol 92 no 4 pp711ndash738 1992

[4] Y Wei C-C Chan J Tian G-W Jang and K F HsuehldquoElectrochemical polymerization of thiophenes in the presenceof bithiophene or terthiophene kinetics and mechanism of thepolymerizationrdquo Chemistry of Materials vol 3 no 5 pp 888ndash897 1991

[5] R M Souto Maior K Hinkelmann H Eckert and FWudl ldquoSynthesis and characterization of two regiochemi-cally defined poly(dialkylbithiophenes) a comparative studyrdquoMacromolecules vol 23 no 5 pp 1268ndash1279 1990

[6] M-A Sato and H Morii ldquoNuclear magnetic resonance stud-ies on electrochemically prepared poly(3-dodecylthiophene)rdquoMacromolecules vol 24 no 5 pp 1196ndash1200 1991

[7] Y-J Cheng S-H Yang and C-S Hsu ldquoSynthesis of conjugatedpolymers for organic solar cell applicationsrdquo Chemical Reviewsvol 109 no 11 pp 5868ndash5923 2009

[8] A C AlgunoW C Chung R V Bantaculo et al ldquoAb initio anddensity functional studies of polythiophene energy band gaprdquoNECTEC Technical Journal vol 2 no 9 pp 215ndash218 2001

[9] J Pei W-L Yu W Huang and A J Heeger ldquoA novel series ofefficient thiophene-based light-emitting conjugated polymersand application in polymer light-emitting diodesrdquo Macro-molecules vol 33 no 7 pp 2462ndash2471 2000

Journal of Chemistry 11

[10] A K Bakhshi ldquoTheoretical tailoring of electrically conductingpolymers some new resultsrdquoMaterials Science and EngineeringC vol 3 no 3-4 pp 249ndash255 1995

[11] M S Senevirathne A Nanayakkara and G K R Senadeera ldquoAtheoretical investigation of band gaps of conducting polymersmdashpolythiophene polypyrrole and polyfuranrdquo inProceedings of the23rd Technical Sessions vol 23 pp 47ndash53 Institute of PhysicsColombo Sri Lanka March 2007

[12] U Salzner J B Lagowski P G Pickup and R A PoirierldquoDesign of low band gap polymers employing density func-tional theorymdashhybrid functionals ameliorate band gap prob-lemrdquo Journal of Computational Chemistry vol 18 no 15 pp1943ndash1953 1997

[13] E Bundgaard and F C Krebs ldquoLow band gap polymers fororganic photovoltaicsrdquo Solar Energy Materials and Solar Cellsvol 91 no 11 pp 954ndash985 2007

[14] M J Frisch G W Trucks H B Schlegel et al ldquoGaussian 09Revision B04rdquo Gaussian Inc Wallingford Conn USA 2009

[15] M E Casida C Jamorski K C Casida and D R SalahubldquoMolecular excitation energies to high-lying bound states fromtime-dependent density-functional response theory charac-terization and correction of the time-dependent local den-sity approximation ionization thresholdrdquo Journal of ChemicalPhysics vol 108 no 11 pp 4439ndash4449 1998

[16] R E Stratmann G E Scuseria and M J Frisch ldquoAn efficientimplementation of time-dependent density-functional theoryfor the calculation of excitation energies of largemoleculesrdquoTheJournal of Chemical Physics vol 109 no 19 pp 8218ndash8224 1998

[17] T Yanai D P Tew and N C Handy ldquoA new hybrid exchange-correlation functional using the Coulomb-attenuating method(CAM-B3LYP)rdquo Chemical Physics Letters vol 393 no 1ndash3 pp51ndash57 2004

[18] J Preat ldquoPhotoinduced energy-transfer and electron-transferprocesses in dye-sensitized solar cells TDDFT insights fortriphenylamine dyesrdquoThe Journal of Physical Chemistry C vol114 no 39 pp 16716ndash16725 2010

[19] B Camino M de La Pierre and A M Ferrari ldquoPhotoelectro-chemical properties of the CT1 dye a DFT studyrdquo Journal ofMolecular Structure vol 1046 pp 116ndash123 2013

[20] A Irfan R Jin A G Al-Sehemi and A M Asiri ldquoQuantumchemical study of the donor-bridge-acceptor triphenylaminebased sensitizersrdquo Spectrochimica Acta Part A Molecular andBiomolecular Spectroscopy vol 110 pp 60ndash66 2013

[21] S Jungsuttiwong R Tarsang T Sudyoadsuk V Promarak PKhongpracha and S Namuangruk ldquoTheoretical study on noveldouble donor-based dyes used in high efficient dye-sensitizedsolar cells the application of TDDFT study to the electroninjection processrdquoOrganic Electronics PhysicsMaterials Appli-cations vol 14 no 3 pp 711ndash722 2013

[22] E J Meijer D M de Leeuw S Setayesh et al ldquoSolution-processed ambipolar organic field-effect transistors and invert-ersrdquo Nature Materials vol 2 no 10 pp 678ndash682 2003

[23] V Hernandez J T L Navarrete and J L Marcos ldquoElectronicstructure and lattice dynamics of polyfuranrdquo Synthetic Metalsvol 41 no 3 pp 789ndash792 1991

[24] F B Kooistra J Knol F Kastenberg et al ldquoIncreasing the opencircuit voltage of bulk-heterojunction solar cells by raising theLUMO level of the acceptorrdquo Organic Letters vol 9 no 4 pp551ndash554 2007

[25] J J M Halls J Cornil D A dos Santos et al ldquoCharge- andenergy-transfer processes at polymerpolymer interfaces a joint

experimental and theoretical studyrdquo Physical Review B vol 60no 8 pp 5721ndash5727 1999

[26] M Fall J-J Aaron and D Gningue-Sall ldquoLuminescence prop-erties of poly(3-methoxythiophene)mdashbithiophene compositeoligomersrdquo Journal of Fluorescence vol 10 no 2 pp 107ndash1112000

[27] M Cossi N Rega G Scalmani and V Barone ldquoEnergiesstructures and electronic properties of molecules in solutionwith the C-PCM solvation modelrdquo Journal of ComputationalChemistry vol 24 no 6 pp 669ndash681 2003

[28] V Barone and M Cossi ldquoQuantum calculation of molecularenergies and energy gradients in solution by a conductor solventmodelrdquoThe Journal of Physical Chemistry A vol 102 no 11 pp1995ndash2001 1998

[29] J F Pan S J Chua and W Huang ldquoQuantum calculationof molecular energies and energy gradients in solution by aconductor solventmodelrdquoChemical Physics Letters vol 363 no1-2 pp 18ndash24 2002

[30] U Salzner J B Lagowski P G Pickup and R A Poirier ldquoCom-parison of geometries and electronic structures of polyacety-lene polyborole polycyclopentadiene polypyrrole polyfuranpolysilole polyphosphole polythiophene polyselenophene andpolytellurophenerdquo Synthetic Metals vol 96 no 3 pp 177ndash1891998

[31] A Kraak and H Wynberg ldquoCharge-transfer interaction ofdithienyls and cyclopentadithiophenes with 135-trinitroben-zene (TNB)rdquo Tetrahedron vol 24 no 10 pp 3881ndash3885 1968

[32] M Dietrich and J Heinze ldquoPoly(441015840-dimethoxybithiophe-ne)mdasha new conducting polymer with extraordinary redox andoptical propertiesrdquo SyntheticMetals vol 41 no 1-2 pp 503ndash5061991

[33] H Zgou M Hamidi M Bouachrine and K Hasnaoui ldquoTheDFT study and opto-electronic properties of copolymers basedon thiophene and phenylenerdquo Physical and Chemical News vol32 pp 81ndash87 2006

[34] L Yang J-K Feng and A-M Ren ldquoTheoretical studies onthe electronic and optical properties of two thiophene-fluorenebased 120587-conjugated copolymersrdquo Polymer vol 46 no 24 pp10970ndash10981 2005

[35] J L Bredas R Silbey D S Boudreaux and R R ChanceldquoChain-length dependence of electronic and electrochemicalproperties of conjugated systems polyacetylene polypheny-lene polythiophene and polypyrrolerdquo Journal of the AmericanChemical Society vol 105 no 22 pp 6555ndash6559 1983

[36] D Fichou G Horowitz B Xu and F Garnier ldquoStoichiometriccontrol of the successive generation of the radical cation anddication of extended 120572-conjugated oligothiophenes a quantita-tive model for doped polythiophenerdquo Synthetic Metals vol 39no 2 pp 243ndash259 1990

[37] D Fichou G Horowitz Y Nishikitani and F Garnier ldquoSemi-conducting conjugated oligomers for molecular electronicsrdquoSynthetic Metals vol 28 no 1-2 pp 723ndash727 1989

[38] V May and O Kuhn Charge and Energy Transfer Dynamics inMolecular Systems Wiley-VCH Berlin Germany 2000

[39] GDennlerMC Scharber andC J Brabec ldquoPolymer-fullerenebulk-heterojunction solar cellsrdquoAdvancedMaterials vol 21 no13 pp 1323ndash1338 2009

[40] JW Chen andY Cao ldquoDevelopment of novel conjugated donorpolymers for high-efficiency bulk-heterojunction photovoltaicdevicesrdquoAccounts of Chemical Research vol 42 no 11 pp 1709ndash1718 2009

12 Journal of Chemistry

[41] Z Cai-Rong L Zi-Jiang C Yu-Hong C Hong-Shan W You-Zhi and Y Li-Hua ldquoDFT and TDDFT study on organic dyesensitizersD5DST andDSS for solar cellsrdquo Journal ofMolecularStructure THEOCHEM vol 899 no 1ndash3 pp 86ndash93 2009

[42] Y He H-Y Chen J Hou and Y Li ldquoIndene-C60bisadduct a

new acceptor for high-performance polymer solar cellsrdquo Journalof the American Chemical Society vol 132 no 4 pp 1377ndash13822010

[43] S Gunes H Neugebauer and N S Sariciftci ldquoConjugatedpolymer-based organic solar cellsrdquo Chemical Reviews vol 107no 4 pp 1324ndash1338 2007

[44] C J Brabec A Cravino D Meissner et al ldquoOrigin of theopen circuit voltage of plastic solar cellsrdquo Advanced FuntionalMaterials vol 11 no 5 pp 374ndash380 2001

[45] M C Scharber D Muhlbacher M Koppe et al ldquoDesign rulesfor donors in bulk-heterojunction solar cellsmdashtowards 10energy-conversion efficiencyrdquo Advanced Materials vol 18 no6 pp 789ndash794 2006

[46] A Gadisa M Svensson M R Andersson and O InganasldquoCorrelation between oxidation potential and open-circuitvoltage of composite solar cells based on blends of polythio-phenesfullerene derivativerdquoApplied Physics Letters vol 84 no9 pp 1609ndash1611 2004

[47] K Kaneto K Yoshino and Y Inuishi ldquoElectrical and opticalproperties of polythiophene prepared by electrochemical poly-merizationrdquo Solid State Communications vol 46 no 5 pp 389ndash391 1983

[48] D Jacquemin J Preat V Wathelet M Fontaine and E APerpete ldquoThioindigo dyes highly accurate visible spectra withTD-DFTrdquo Journal of the American Chemical Society vol 128 no6 pp 2072ndash2083 2006

[49] N Santhanamoorthi K Senthilkumar and P KolandaivelldquoTautomerization and solvent effects on the absorption andemission properties of the Schiff base NN1015840-bis(salicylidene)-p-phenylenediaminemdasha TDDFT studyrdquoMolecular Physics vol108 no 14 pp 1817ndash1827 2010

[50] J Vasudevan R T Stibrany J Bumby et al ldquoAn edge-over-edgeZn(II) bacteriochlorin dimer having an unshifted Q

119910bandThe

importance of 120587-overlaprdquo Journal of the American ChemicalSociety vol 118 no 46 pp 11676ndash11677 1996

[51] H Scheer and H H Inhoffen ldquoHydroporphyrins reactivityspectroscopy and hydroporphyrin analoguesrdquo in The Por-phyrins DDolphin Ed vol 2 pp 45ndash90 Academic Press NewYork NY USA 1978

[52] R H Friend R W Gymer A B Holmes et al ldquoElectrolumi-nescence in conjugated polymersrdquoNature vol 397 no 6715 pp121ndash128 1999

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

Journal of Chemistry 11

[10] A K Bakhshi ldquoTheoretical tailoring of electrically conductingpolymers some new resultsrdquoMaterials Science and EngineeringC vol 3 no 3-4 pp 249ndash255 1995

[11] M S Senevirathne A Nanayakkara and G K R Senadeera ldquoAtheoretical investigation of band gaps of conducting polymersmdashpolythiophene polypyrrole and polyfuranrdquo inProceedings of the23rd Technical Sessions vol 23 pp 47ndash53 Institute of PhysicsColombo Sri Lanka March 2007

[12] U Salzner J B Lagowski P G Pickup and R A PoirierldquoDesign of low band gap polymers employing density func-tional theorymdashhybrid functionals ameliorate band gap prob-lemrdquo Journal of Computational Chemistry vol 18 no 15 pp1943ndash1953 1997

[13] E Bundgaard and F C Krebs ldquoLow band gap polymers fororganic photovoltaicsrdquo Solar Energy Materials and Solar Cellsvol 91 no 11 pp 954ndash985 2007

[14] M J Frisch G W Trucks H B Schlegel et al ldquoGaussian 09Revision B04rdquo Gaussian Inc Wallingford Conn USA 2009

[15] M E Casida C Jamorski K C Casida and D R SalahubldquoMolecular excitation energies to high-lying bound states fromtime-dependent density-functional response theory charac-terization and correction of the time-dependent local den-sity approximation ionization thresholdrdquo Journal of ChemicalPhysics vol 108 no 11 pp 4439ndash4449 1998

[16] R E Stratmann G E Scuseria and M J Frisch ldquoAn efficientimplementation of time-dependent density-functional theoryfor the calculation of excitation energies of largemoleculesrdquoTheJournal of Chemical Physics vol 109 no 19 pp 8218ndash8224 1998

[17] T Yanai D P Tew and N C Handy ldquoA new hybrid exchange-correlation functional using the Coulomb-attenuating method(CAM-B3LYP)rdquo Chemical Physics Letters vol 393 no 1ndash3 pp51ndash57 2004

[18] J Preat ldquoPhotoinduced energy-transfer and electron-transferprocesses in dye-sensitized solar cells TDDFT insights fortriphenylamine dyesrdquoThe Journal of Physical Chemistry C vol114 no 39 pp 16716ndash16725 2010

[19] B Camino M de La Pierre and A M Ferrari ldquoPhotoelectro-chemical properties of the CT1 dye a DFT studyrdquo Journal ofMolecular Structure vol 1046 pp 116ndash123 2013

[20] A Irfan R Jin A G Al-Sehemi and A M Asiri ldquoQuantumchemical study of the donor-bridge-acceptor triphenylaminebased sensitizersrdquo Spectrochimica Acta Part A Molecular andBiomolecular Spectroscopy vol 110 pp 60ndash66 2013

[21] S Jungsuttiwong R Tarsang T Sudyoadsuk V Promarak PKhongpracha and S Namuangruk ldquoTheoretical study on noveldouble donor-based dyes used in high efficient dye-sensitizedsolar cells the application of TDDFT study to the electroninjection processrdquoOrganic Electronics PhysicsMaterials Appli-cations vol 14 no 3 pp 711ndash722 2013

[22] E J Meijer D M de Leeuw S Setayesh et al ldquoSolution-processed ambipolar organic field-effect transistors and invert-ersrdquo Nature Materials vol 2 no 10 pp 678ndash682 2003

[23] V Hernandez J T L Navarrete and J L Marcos ldquoElectronicstructure and lattice dynamics of polyfuranrdquo Synthetic Metalsvol 41 no 3 pp 789ndash792 1991

[24] F B Kooistra J Knol F Kastenberg et al ldquoIncreasing the opencircuit voltage of bulk-heterojunction solar cells by raising theLUMO level of the acceptorrdquo Organic Letters vol 9 no 4 pp551ndash554 2007

[25] J J M Halls J Cornil D A dos Santos et al ldquoCharge- andenergy-transfer processes at polymerpolymer interfaces a joint

experimental and theoretical studyrdquo Physical Review B vol 60no 8 pp 5721ndash5727 1999

[26] M Fall J-J Aaron and D Gningue-Sall ldquoLuminescence prop-erties of poly(3-methoxythiophene)mdashbithiophene compositeoligomersrdquo Journal of Fluorescence vol 10 no 2 pp 107ndash1112000

[27] M Cossi N Rega G Scalmani and V Barone ldquoEnergiesstructures and electronic properties of molecules in solutionwith the C-PCM solvation modelrdquo Journal of ComputationalChemistry vol 24 no 6 pp 669ndash681 2003

[28] V Barone and M Cossi ldquoQuantum calculation of molecularenergies and energy gradients in solution by a conductor solventmodelrdquoThe Journal of Physical Chemistry A vol 102 no 11 pp1995ndash2001 1998

[29] J F Pan S J Chua and W Huang ldquoQuantum calculationof molecular energies and energy gradients in solution by aconductor solventmodelrdquoChemical Physics Letters vol 363 no1-2 pp 18ndash24 2002

[30] U Salzner J B Lagowski P G Pickup and R A Poirier ldquoCom-parison of geometries and electronic structures of polyacety-lene polyborole polycyclopentadiene polypyrrole polyfuranpolysilole polyphosphole polythiophene polyselenophene andpolytellurophenerdquo Synthetic Metals vol 96 no 3 pp 177ndash1891998

[31] A Kraak and H Wynberg ldquoCharge-transfer interaction ofdithienyls and cyclopentadithiophenes with 135-trinitroben-zene (TNB)rdquo Tetrahedron vol 24 no 10 pp 3881ndash3885 1968

[32] M Dietrich and J Heinze ldquoPoly(441015840-dimethoxybithiophe-ne)mdasha new conducting polymer with extraordinary redox andoptical propertiesrdquo SyntheticMetals vol 41 no 1-2 pp 503ndash5061991

[33] H Zgou M Hamidi M Bouachrine and K Hasnaoui ldquoTheDFT study and opto-electronic properties of copolymers basedon thiophene and phenylenerdquo Physical and Chemical News vol32 pp 81ndash87 2006

[34] L Yang J-K Feng and A-M Ren ldquoTheoretical studies onthe electronic and optical properties of two thiophene-fluorenebased 120587-conjugated copolymersrdquo Polymer vol 46 no 24 pp10970ndash10981 2005

[35] J L Bredas R Silbey D S Boudreaux and R R ChanceldquoChain-length dependence of electronic and electrochemicalproperties of conjugated systems polyacetylene polypheny-lene polythiophene and polypyrrolerdquo Journal of the AmericanChemical Society vol 105 no 22 pp 6555ndash6559 1983

[36] D Fichou G Horowitz B Xu and F Garnier ldquoStoichiometriccontrol of the successive generation of the radical cation anddication of extended 120572-conjugated oligothiophenes a quantita-tive model for doped polythiophenerdquo Synthetic Metals vol 39no 2 pp 243ndash259 1990

[37] D Fichou G Horowitz Y Nishikitani and F Garnier ldquoSemi-conducting conjugated oligomers for molecular electronicsrdquoSynthetic Metals vol 28 no 1-2 pp 723ndash727 1989

[38] V May and O Kuhn Charge and Energy Transfer Dynamics inMolecular Systems Wiley-VCH Berlin Germany 2000

[39] GDennlerMC Scharber andC J Brabec ldquoPolymer-fullerenebulk-heterojunction solar cellsrdquoAdvancedMaterials vol 21 no13 pp 1323ndash1338 2009

[40] JW Chen andY Cao ldquoDevelopment of novel conjugated donorpolymers for high-efficiency bulk-heterojunction photovoltaicdevicesrdquoAccounts of Chemical Research vol 42 no 11 pp 1709ndash1718 2009

12 Journal of Chemistry

[41] Z Cai-Rong L Zi-Jiang C Yu-Hong C Hong-Shan W You-Zhi and Y Li-Hua ldquoDFT and TDDFT study on organic dyesensitizersD5DST andDSS for solar cellsrdquo Journal ofMolecularStructure THEOCHEM vol 899 no 1ndash3 pp 86ndash93 2009

[42] Y He H-Y Chen J Hou and Y Li ldquoIndene-C60bisadduct a

new acceptor for high-performance polymer solar cellsrdquo Journalof the American Chemical Society vol 132 no 4 pp 1377ndash13822010

[43] S Gunes H Neugebauer and N S Sariciftci ldquoConjugatedpolymer-based organic solar cellsrdquo Chemical Reviews vol 107no 4 pp 1324ndash1338 2007

[44] C J Brabec A Cravino D Meissner et al ldquoOrigin of theopen circuit voltage of plastic solar cellsrdquo Advanced FuntionalMaterials vol 11 no 5 pp 374ndash380 2001

[45] M C Scharber D Muhlbacher M Koppe et al ldquoDesign rulesfor donors in bulk-heterojunction solar cellsmdashtowards 10energy-conversion efficiencyrdquo Advanced Materials vol 18 no6 pp 789ndash794 2006

[46] A Gadisa M Svensson M R Andersson and O InganasldquoCorrelation between oxidation potential and open-circuitvoltage of composite solar cells based on blends of polythio-phenesfullerene derivativerdquoApplied Physics Letters vol 84 no9 pp 1609ndash1611 2004

[47] K Kaneto K Yoshino and Y Inuishi ldquoElectrical and opticalproperties of polythiophene prepared by electrochemical poly-merizationrdquo Solid State Communications vol 46 no 5 pp 389ndash391 1983

[48] D Jacquemin J Preat V Wathelet M Fontaine and E APerpete ldquoThioindigo dyes highly accurate visible spectra withTD-DFTrdquo Journal of the American Chemical Society vol 128 no6 pp 2072ndash2083 2006

[49] N Santhanamoorthi K Senthilkumar and P KolandaivelldquoTautomerization and solvent effects on the absorption andemission properties of the Schiff base NN1015840-bis(salicylidene)-p-phenylenediaminemdasha TDDFT studyrdquoMolecular Physics vol108 no 14 pp 1817ndash1827 2010

[50] J Vasudevan R T Stibrany J Bumby et al ldquoAn edge-over-edgeZn(II) bacteriochlorin dimer having an unshifted Q

119910bandThe

importance of 120587-overlaprdquo Journal of the American ChemicalSociety vol 118 no 46 pp 11676ndash11677 1996

[51] H Scheer and H H Inhoffen ldquoHydroporphyrins reactivityspectroscopy and hydroporphyrin analoguesrdquo in The Por-phyrins DDolphin Ed vol 2 pp 45ndash90 Academic Press NewYork NY USA 1978

[52] R H Friend R W Gymer A B Holmes et al ldquoElectrolumi-nescence in conjugated polymersrdquoNature vol 397 no 6715 pp121ndash128 1999

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

12 Journal of Chemistry

[41] Z Cai-Rong L Zi-Jiang C Yu-Hong C Hong-Shan W You-Zhi and Y Li-Hua ldquoDFT and TDDFT study on organic dyesensitizersD5DST andDSS for solar cellsrdquo Journal ofMolecularStructure THEOCHEM vol 899 no 1ndash3 pp 86ndash93 2009

[42] Y He H-Y Chen J Hou and Y Li ldquoIndene-C60bisadduct a

new acceptor for high-performance polymer solar cellsrdquo Journalof the American Chemical Society vol 132 no 4 pp 1377ndash13822010

[43] S Gunes H Neugebauer and N S Sariciftci ldquoConjugatedpolymer-based organic solar cellsrdquo Chemical Reviews vol 107no 4 pp 1324ndash1338 2007

[44] C J Brabec A Cravino D Meissner et al ldquoOrigin of theopen circuit voltage of plastic solar cellsrdquo Advanced FuntionalMaterials vol 11 no 5 pp 374ndash380 2001

[45] M C Scharber D Muhlbacher M Koppe et al ldquoDesign rulesfor donors in bulk-heterojunction solar cellsmdashtowards 10energy-conversion efficiencyrdquo Advanced Materials vol 18 no6 pp 789ndash794 2006

[46] A Gadisa M Svensson M R Andersson and O InganasldquoCorrelation between oxidation potential and open-circuitvoltage of composite solar cells based on blends of polythio-phenesfullerene derivativerdquoApplied Physics Letters vol 84 no9 pp 1609ndash1611 2004

[47] K Kaneto K Yoshino and Y Inuishi ldquoElectrical and opticalproperties of polythiophene prepared by electrochemical poly-merizationrdquo Solid State Communications vol 46 no 5 pp 389ndash391 1983

[48] D Jacquemin J Preat V Wathelet M Fontaine and E APerpete ldquoThioindigo dyes highly accurate visible spectra withTD-DFTrdquo Journal of the American Chemical Society vol 128 no6 pp 2072ndash2083 2006

[49] N Santhanamoorthi K Senthilkumar and P KolandaivelldquoTautomerization and solvent effects on the absorption andemission properties of the Schiff base NN1015840-bis(salicylidene)-p-phenylenediaminemdasha TDDFT studyrdquoMolecular Physics vol108 no 14 pp 1817ndash1827 2010

[50] J Vasudevan R T Stibrany J Bumby et al ldquoAn edge-over-edgeZn(II) bacteriochlorin dimer having an unshifted Q

119910bandThe

importance of 120587-overlaprdquo Journal of the American ChemicalSociety vol 118 no 46 pp 11676ndash11677 1996

[51] H Scheer and H H Inhoffen ldquoHydroporphyrins reactivityspectroscopy and hydroporphyrin analoguesrdquo in The Por-phyrins DDolphin Ed vol 2 pp 45ndash90 Academic Press NewYork NY USA 1978

[52] R H Friend R W Gymer A B Holmes et al ldquoElectrolumi-nescence in conjugated polymersrdquoNature vol 397 no 6715 pp121ndash128 1999

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of