ABSTRACT A convenient, facile synthesis of a series of stabilized acenes that incorporate several...
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6,13-B IS-2,6-D IETH YLPH EN YLPEN TAC EN E -0.1 0.1 0.3 0.5 0.7 0.9 1.1 1.3 320 370 420 470 520 570 620 W AVELENGTH (nm ) A B SO R B A N C E (A ) NO LIGHT 5 SEC 100 SEC 200 SEC 300 SEC 420 SEC 570 SEC 660 SEC 750 SEC 840 SEC 1065 SEC 1200 SEC 1320 SEC 1440 SEC 1620 SEC 1740 SEC 1860 SEC 2040 SEC 2220 SEC ABSTRACT ABSTRACT A convenient, facile A convenient, facile synthesis of a series of synthesis of a series of stabilized acenes that stabilized acenes that incorporate several incorporate several different aryl substituents different aryl substituents located at different located at different positions along the acene positions along the acene backbone is described. backbone is described. These structurally modified These structurally modified acenes show vastly improved acenes show vastly improved solubility (processability) solubility (processability) and greater photooxidative and greater photooxidative stability. stability. INTRODUCTION INTRODUCTION During the last few years, During the last few years, the development of organic the development of organic thin film transistors thin film transistors (OTFTs) has attracted much (OTFTs) has attracted much interest because organic interest because organic molecules can be deposited molecules can be deposited over large surface areas over large surface areas and are compatible with and are compatible with flexible plastic flexible plastic substrates[1]. substrates[1]. Pentacene molecules have Pentacene molecules have been deposited on a wide been deposited on a wide variety of materials to variety of materials to build flexible electronics. build flexible electronics. Acenes including Acenes including pentacene has been utilized pentacene has been utilized in photovoltaics, organic in photovoltaics, organic light emitting diodes light emitting diodes (OLEDs) and other (OLEDs) and other electronic applications. electronic applications. Problems encountered Problems encountered include a lack of include a lack of solubility and photo- solubility and photo- OUR APPROACH TO OUR APPROACH TO PERSISTENT PENTACENES PERSISTENT PENTACENES The most reactive rings on pentacene The most reactive rings on pentacene are those indicated with arrows. We are those indicated with arrows. We have prepared several pentacene have prepared several pentacene derivatives in which these sites derivatives in which these sites exhibit varying degrees of steric exhibit varying degrees of steric hindrance hindrance CONCLUSIONS CONCLUSIONS Modified pentacenes show enhanced photo-oxidative stability and Modified pentacenes show enhanced photo-oxidative stability and improved solubility improved solubility Increasing the alkyl chain length at the ortho position of the phenyl Increasing the alkyl chain length at the ortho position of the phenyl substituents substituents increases the kinetic stability of the corresponding increases the kinetic stability of the corresponding acene acene 6,13-disubstituted pentacenes show greater photooxidative stability 6,13-disubstituted pentacenes show greater photooxidative stability than 5,7,12,14- than 5,7,12,14- tetrasubstituted pentacenes. Thus, the center-most tetrasubstituted pentacenes. Thus, the center-most rings are most prone to oxidation rings are most prone to oxidation and should be the focus of further and should be the focus of further synthetic efforts to prepare persistent acenes. synthetic efforts to prepare persistent acenes. FORMATION AND STABILITY STUDIES OF PERSISTENT ACENES FORMATION AND STABILITY STUDIES OF PERSISTENT ACENES Irvinder Kaur Irvinder Kaur and Glen P. Miller and Glen P. Miller University of New Hampshire University of New Hampshire This work was supported under the Nanoscale Science and Engineering Centers Program of the National Science Foundation (Award # NSF-0425826) 5,7,12,14-Tetrasubstituted Pentacenes 6,13-Disubstituted Pentacenes SYNTHETIC DETAILS SYNTHETIC DETAILS 6,13-Disubstituted Pentacenes 6,13-Disubstituted Pentacenes 5,7,12,14-Tetrasubstituted Pentacenes 5,7,12,14-Tetrasubstituted Pentacenes RESULTS RESULTS UV-Vis Data: IMPROVED PHOTOOXIDATIVE STABILITY UV-Vis Data: IMPROVED PHOTOOXIDATIVE STABILITY Change in UV-Vis spectrum of structurally modified pentacene upon exposure to light in ambient atmosphere 1.2 1.0 0.8 0.6 0.4 0.2 0.0 A bsorbance (a.u.) 700 600 500 400 300 200 100 0 Tim e (m in) (B) (A) (C) (D) (E) (i) (ii) 4 hr 7 min 0 min 8 hr (i) (ii) (i) (ii) (i) (ii) (i) (ii) PICTORIAL EVIDENCE PICTORIAL EVIDENCE WHY SHOULD STRUCTURALLY MODIFIED WHY SHOULD STRUCTURALLY MODIFIED PENTACENES RESIST PHOTO-OXIDATION? PENTACENES RESIST PHOTO-OXIDATION? Phenyl rings of the modified acene lie nearly perpendicular to the plane of the acene unit. The alkyl groups are expected to lie above and below the most reactive sites and therefore impede the approach of oxygen. REFERENCES REFERENCES [1] J. Briggs and G. Miller Comptes Rendus Chimie, 2006, 9, 916. [2] W. Dehaen et al Synlett, 2005, 2, 217. STABILITY STABILITY SOLUBILITY SOLUBILITY Comparison of several different structurally modified pentacene Absorbance at different max of a single structurally modified pentacene with time 6,13-B IS-2,6-D IETH YLPH EN YLPEN TAC EN E -0.1 0.1 0.3 0.5 0.7 0.9 1.1 1.3 0 5000 10000 15000 20000 25000 30000 35000 TIM E (SEC) ABSORBANCE (A) Abs (336) Abs (354) Abs (368) Abs (388) Abs (520) Abs (558) Abs (605) N 2 -78 C 0 C , o o NaI, N aH 2 PO 2 N 2 , 1.5 h Dark, 90-94% HO OH OH HO R R R R R R R R 16 h, 52-55% HOAc O O O O O O AlCl 3 , 4 h, reflux O Ph OH O HO O Ph O O O O O H 2 SO 4 4-5 h, 100 o C 72% R R R R R R R R R =H , C H 3 R R Li O O + Br Br Br Br NaI, D M F 120 C, 16h 90% o O O OH OH R R N 2 -78 C 0 C , o o R R N aI, N aH 2 PO 2 H O A c, N 2 , 1.5h Dark, 88-92% 16 h, 50-62% R R R R R =H , C H 3 , C 2 H 5 R R Li PENTACENE ANTHRACENE 2 2 MECHANISTIC INSIGHTS… Photo-oxidation of pentacene is believed to require two approaches by oxygen. First, triplet oxygen is converted to singlet oxygen via photoexcited pentacene. Second, singlet oxygen cycloadds across the acene in a [4+2] fashion. Sterically hindered pentacenes can gain kinetic stability by slowing either or both of these steps. A B C D E
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Transcript of ABSTRACT A convenient, facile synthesis of a series of stabilized acenes that incorporate several...
6,13-BIS-2,6-DIETHYLPHENYLPENTACENE
-0.1
0.1
0.3
0.5
0.7
0.9
1.1
1.3
320 370 420 470 520 570 620
WAVELENGTH (nm)
AB
SO
RB
AN
CE
(A)
NO LIGHT
5 SEC
100 SEC
200 SEC
300 SEC
420 SEC
570 SEC
660 SEC
750 SEC
840 SEC
1065 SEC
1200 SEC
1320 SEC
1440 SEC
1620 SEC
1740 SEC
1860 SEC
2040 SEC
2220 SEC
2400 SEC
ABSTRACTABSTRACT
A convenient, facile synthesis A convenient, facile synthesis of a series of stabilized acenes of a series of stabilized acenes that incorporate several different that incorporate several different aryl substituents located at aryl substituents located at different positions along the different positions along the acene backbone is described. acene backbone is described. These structurally modified These structurally modified acenes show vastly improved acenes show vastly improved solubility (processability) and solubility (processability) and greater photooxidative stability.greater photooxidative stability.
INTRODUCTIONINTRODUCTION
During the last few years, the During the last few years, the development of organic thin film development of organic thin film transistors (OTFTs) has attracted transistors (OTFTs) has attracted much interest because organic much interest because organic molecules can be deposited over molecules can be deposited over large surface areas and are large surface areas and are compatible with flexible plastic compatible with flexible plastic substrates[1].substrates[1].
Pentacene molecules have Pentacene molecules have been deposited on a wide variety been deposited on a wide variety of materials to build flexible of materials to build flexible electronics.electronics. Acenes including pentacene Acenes including pentacene has been utilized in photovoltaics, has been utilized in photovoltaics, organic light emitting diodes organic light emitting diodes (OLEDs) and other electronic (OLEDs) and other electronic applications.applications.Problems encountered include a Problems encountered include a lack of solubility and photo-lack of solubility and photo-oxidative instability.oxidative instability.
OUR APPROACH TO OUR APPROACH TO PERSISTENT PENTACENESPERSISTENT PENTACENES
The most reactive rings on pentacene are those The most reactive rings on pentacene are those indicated with arrows. We have prepared several indicated with arrows. We have prepared several pentacene derivatives in which these sites exhibit pentacene derivatives in which these sites exhibit varying degrees of steric hindrancevarying degrees of steric hindrance
CONCLUSIONSCONCLUSIONS Modified pentacenes show enhanced photo-oxidative stability and improved solubilityModified pentacenes show enhanced photo-oxidative stability and improved solubility Increasing the alkyl chain length at the ortho position of the phenyl substituents Increasing the alkyl chain length at the ortho position of the phenyl substituents increases the kinetic stability of the corresponding aceneincreases the kinetic stability of the corresponding acene 6,13-disubstituted pentacenes show greater photooxidative stability than 5,7,12,14-6,13-disubstituted pentacenes show greater photooxidative stability than 5,7,12,14-tetrasubstituted pentacenes. Thus, the center-most rings are most prone to oxidation tetrasubstituted pentacenes. Thus, the center-most rings are most prone to oxidation and and should be the focus of further synthetic efforts to prepare persistent acenes. should be the focus of further synthetic efforts to prepare persistent acenes.
FORMATION AND STABILITY STUDIES OF PERSISTENT ACENESFORMATION AND STABILITY STUDIES OF PERSISTENT ACENESIrvinder KaurIrvinder Kaur and Glen P. Miller and Glen P. Miller
University of New HampshireUniversity of New Hampshire
This work was supported under the Nanoscale Science and Engineering Centers Program of the National Science Foundation (Award # NSF-0425826)
5,7,12,14-Tetrasubstituted Pentacenes
6,13-Disubstituted Pentacenes
SYNTHETIC DETAILSSYNTHETIC DETAILS6,13-Disubstituted Pentacenes6,13-Disubstituted Pentacenes
5,7,12,14-Tetrasubstituted Pentacenes5,7,12,14-Tetrasubstituted Pentacenes
RESULTSRESULTSUV-Vis Data: IMPROVED PHOTOOXIDATIVE STABILITYUV-Vis Data: IMPROVED PHOTOOXIDATIVE STABILITY
Change in UV-Vis spectrum of structurally modified pentacene upon exposure to light
in ambient atmosphere
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Ab
sorb
ance
(a.
u.)
7006005004003002001000Time (min)
(B)(A) (C) (D) (E)
(i) (ii)
4 hr7 min0 min 8 hr(i) (ii) (i) (ii) (i) (ii) (i) (ii)
PICTORIAL EVIDENCEPICTORIAL EVIDENCE
WHY SHOULD STRUCTURALLY MODIFIED WHY SHOULD STRUCTURALLY MODIFIED PENTACENES RESIST PHOTO-OXIDATION?PENTACENES RESIST PHOTO-OXIDATION?
Phenyl rings of the modified acene lie nearly perpendicular to the plane of the acene unit. The alkyl groups are expected to lie above and below the most reactive sites and therefore impede the approach of oxygen.
REFERENCESREFERENCES[1] J. Briggs and G. Miller Comptes Rendus Chimie, 2006, 9, 916.[2] W. Dehaen et al Synlett, 2005, 2, 217.
STABILITYSTABILITY SOLUBILITYSOLUBILITY
Comparison of several different structurally modified pentacene
Absorbance at different max of a single structurally modified pentacene with time
6,13-BIS-2,6-DIETHYLPHENYLPENTACENE
-0.1
0.1
0.3
0.5
0.7
0.9
1.1
1.3
0 5000 10000 15000 20000 25000 30000 35000
TIME (SEC)
AB
SO
RB
AN
CE
(A)
Abs(336)Abs(354)Abs(368)Abs(388)Abs(520)Abs(558)Abs(605)
N2-78 C 0 C,o o
NaI, NaH2PO2
N2, 1.5 hDark, 90-94%
HOOH
OH HO
RR R
R
RRR
R16 h, 52-55%
HOAc
OO
O O
OO
AlCl3,
4 h, reflux
O
PhOH
O
HO
O
Ph
O
O
O
O
O
H2SO4
4-5 h, 100o C 72%
R R
RRR R
RR
R=H, CH3
R
R
Li
O
O
+
Br
Br
Br
Br
NaI, DMF
120 C, 16h 90%
o
O
O
OH
OHR
R
N2 -78 C 0 C,o o
R
R
NaI, NaH2PO2
HOAc, N2, 1.5hDark, 88-92%
16 h, 50-62%
R R
RR
R=H, CH3, C2H5
R
R
L i
PENTACENE
ANTHRACENE
2
2
MECHANISTIC INSIGHTS…
Photo-oxidation of pentacene is believed to require two approaches by oxygen. First, triplet oxygen is converted to singlet oxygen via photoexcited pentacene. Second, singlet oxygen cycloadds across the acene in a [4+2] fashion. Sterically hindered pentacenes can gain kinetic stability by slowing either or both of these steps.
A
B
C
D E
