SYNTHESIS AND CHARACTERIZATION OF FLUORENE BASED OLIGOMERS ... · SYNTHESIS AND CHARACTERIZATION OF...

SYNTHESIS AND CHARACTERIZATION OF FLUORENE BASED OLIGOMERS AND POLYMERS

CAI LIPING

(MSc LANZHOU Univ.)

A THESIS SUBMITED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY

DEPARTMENT OF CHEMISTRY NATIONAL UNIVERSITY OF SINGAPORE

2009

i

ACKNOWLEDGEMENTS

My most sincere gratitude goes out to my supervisor, Assoc. Prof. Lai Yee Hing, who

gave me the opportunity to purse a Ph. D. degree in the National University of Singapore

(NUS). Thanks him for his invaluable guidance, constant encouragement and great

support throughout my study. I gratefully appreciate the freedom he gave me to delve

into various aspects of this research.

The memories of my good times in the laboratory with Dr. Xu Jianwei, Dr. Wang Fuke,

Dr. Wang Weiling, Dr. Teo Tang Lin, Mr. Wang Jianhua, Mr. LuYong, Mr. Fang Zhen,

Mr. Chen Zhongyao and Mr. Wee Chorng Shin will remain with me forever.

I would like to thank the staffs at the chemical store and the Chemical and Molecular

Analysis Center of Chemistry Department for their technical assistance in various

analyses such as NMR, MS, EA. Special thanks also goes to the National University of

Singapore for awarding me a research scholarship.

Lastly, special mention must be made to my father, mother and wife. Thank them for

their deep loving encouragement and patience. Thank you.

Table of Contents

Acknowledgement i

Table of Contents ii

Summary vii

List of Tables ix

List of Figures x

Chapter 1 Introduction 1

1.1 Conjugated polymers 1

1.1.1 Structure of conjugated polymer 1

1.1.2 Bandgap of conjugated polymers 5

1.1.3 Fluorecence from conjugated polymers 7

1.1.4 Application of conjugated polymers 12

1.2 Polyfluorene as light emitting polymer 13

1.3 Organic light emitting diodes (OLED) 15

1.3.1 Hole transporting material, HTM 15

1.3.2 Electron transporting material (ETL) 21

1.3.2.1 Organometallic ETL compounds 21

1.3.2.2 Non-Organometallic ETL compounds 23

1.3.3 Bule light emitting materials 28

1.3.4 Green light emitting materials 34

1.3.5 Red light emitting materials 38

1.3.6 Hole Blocking materials 44

ii

1.4 Project objectives 46

Reference 51

Chapter 2 Synthesis and Characterization of Chromophore-Side

Chains PPV Derivatives 64

2.1 Introduction 64

2.1.1 Main synthesis routes of PPV compounds 64

2.1.1.1 Sulfonium precursor route 64

2.1.1.2 Side chain derivatization 65

2.1.1.3 Polycondensation methods 66

2.1.1.4 Ring-opening metathesis polymerization (ROMP) 67

2.1.2 Application of PPV and Derivatives 68

2.2 Molecular design 68

2.3. Synthesis route 69

2.4 Results and discussion 72

2.4.1 Polymer synthesis 72

2.4.2 Size exclusion chromatography (SEC) 73

2.4.3 Thermal Analysis (TGA and DSC) 74

2.4.4 Optical Properties (UV and PL) 75

2.4.5 Electrochemical Properties 77

2.4 Conclusion 78

Reference 80

iii

Chapter 3 Synthesis and characterization of tetrabenzo[5.5]fulvalene

based polymers 83

3.1 Introduction 83



3.3.1 Size exclusion chromatography (SEC) 87




3.3.5 Comparison of our novel polymers with some analogues 92

3.4 Conclusion 93

Reference 94

Chapter 4 Synthesis and Characterization of Chromophore Substituted

[2.2]Paracyclophane Derivatives 96

4.1 Introduction 96

4.1.1 Cyclophane-containing Polymers 96

4.1.1.1 [2.2] Paracyclophane-containing polymers 97

4.1.1.2 Rigid-rod conjugated polymers containing

pendent aromatic rings 98

4.1.2 Cyclophane chiral ligands 100

4.1.3 Cyclophane nonlinear optical materials 101

4.1.3.1 Synthesis and characterization of chromophores

iv

substituted [2.2]paracyclophanes 102

4.1.3.2 Two photon absorption (TPA) performance

of paracyclophenes 103

4.1.3.3 Charge transport through paracyclophanes 104

4.2 Molecular Design 105

4.3 Synthesis and characterization 107

4.3.1 Synthesis of (4,7,12,15)-Terta(9,9-di-n-hexyl-fluoren-2-yl)

[2,2]paracyclophane (2F2F) 107

4.3.2 Synthesis of (4,7,12,15)-Terta(N-n-hexylcarbazole -3 -yl)

[2,2]paracyclophane (2C2C) and (4,7)-Bis(9,9-di-n-hexyl-

fluorene-2-yl)-(12,15)-bis(N-n- hexylcarbazole -3 -yl)

[2,2]paracyclophane (2F2C) 109

4.3.3 Synthesis of (4,7)-Bis(9,9-di-n-hexyl-fluoren-2-yl)-(12,15)-

bis(thiophene-2-yl) [2,2]paracyclophane (2F2T) and (4,7)-

Bis(N-n-hexylcarbazole-3-yl)-(12,15)-bis(thiophene-2-yl)

[2,2]paracyclophane (2C2T) 112

4.4 Results and Discussion 114

4.4.1 Synthesis methodology 114

4.4.2 NMR spectrum 117

4.4.3 MALDI-TOF mass spectrum 120



4.5 Conclusion 133

v

Reference 134

Chapter 5 Synthesis and Characterization of Hexafluorenyl Benzene 140

5.1 Introduction 140



5.3.1 NMR spectroscopy 144

5.3.2 MALDI-TOF mass spectrum 146




5.4 Conclusion 151

Reference 153

Chapter 6 Experimental Section 154

6.1 Monomers and Polymers Synthesized in Chapter Two 154

6.2 Monomers and Polymers Synthesized in Chapter Three 162

6.3 Molecules Synthesized in Chapter Four 167

6.4 Molecules Synthesized in Chapter Five 178

Reference 183

Appendix I Characterization techniques I

vi

Summary

Organic conjugated polymers have been thoroughly investigated over the past twenty

years due to their promising electronic and optical applications. Current research interests

on conjugated polymers focus on tuning their spectral and electrical properties. During

these researches, polyfluorene emerged as a very attractive class of conjugated polymers,

especially for display applications, owing to their pure blue and efficient

electroluminescence coupled with a high charge-carrier mobility and good processability.

In our work, four series of fluorene based new polymers and oligomers will be reported.

In the work of PPV derivatives polymers synthesis (Chapter two), two novel

dichromophore side chains substituted PPV compounds were successfully synthesized.

Two key steps in the whole synthesis route were aromatic CH2Br groups’ protection and

deprotection reactions. The high yields of these two reactions were guarantee of the

success of whole route. Efficient green light emission, good solubility in common organic

solvents, good thermal stability and relative high glass transition temperatures had been

demonstrated in these two polymers. These properties made the two polymers good

candidates for efficient green light emitting devices

In order to investigate the effect of bistricyclic aromatic system on the polymer

backbone, two novel tetrabenzo[5.5]fulvalene units containing polymers were

successfully synthesized (Chapter three). Good solubility in common organic solvents,

good thermal stability and relative high glass transition temperatures had been

demonstrated in these two polymers. Although the quantum yield of the two polymers

were low due to the good packing of the tetrabenzo[5.5]fulvalene units. These

vii

compounds can still have the potential to be used as solar cell and organic field effect

transistor materials.

Compared with polymers, oligomers generally have more predictable and reproducible

properties that are amenable to have optimization through molecular engineering. In our

work of Chapter four, five tetra-substituted [2.2]paracyclophane oligomers were obtained

in high yields. Two key step reactions, which are HBr gas deprotecting reaction and UV

irradiation reaction, gave satisfactory yield of whole synthesis route. Efficient blue light

emission, good solubility in common organic solvents had been demonstrated in all of the

five compounds. The optical and electrochemical properties all exhibited dependence on

the changes of different substituted chromorphores on the [2.2]paracyclophane core.

Modification on the substitution groups with different electron-donating and electron-

withdrawing groups on the [2.2]paracyclophane core enabled the tuning of HOMO and

LUMO energy levels. This freely modification makes the synthesis route very useful to

obtain different [2.2] paracyclophanes derivatives which can be used in different

applications areas such as asymmetric reaction, OLED and NLO materials.

In our last chapter work, a convenient approach to synthesize high steric hindrance

hexafluorenyl benzene was successfully established (Chapter Five). Detailed reaction

conditions were discussed. This compound can be a theory model of conformational

mobile system.

In conclusion, by the different synthetic modification, fluorene based polymers and

oligomers can be more useful in different materials application.

viii

List of Tables

Tables Page

Table 1.1 Some Important Conjugated Polymers 2

Table 2.1 The SEC data of polymer P1 and P2 73

Table 2.2 The optical data and fluorescence quantum yields

(both in chloroform solutions) of polymer P1 and P2 76

Table 2.3 The electrochemical data of the polymers P1 and P2 78

Table 3.1 The SEC data of polymer P1 and P2 87


(both in chloroform solutions) of polymer P1 and P2 90

Table 3.3 The electrochemical data of the polymers P1 and P2 91

Table 4.1 The optical data of [2.2]paracyclophanes and their precursors

[3.3]dithioparacyclophane in chloroform solution 129

Table 4.2 The electrochemical data of [2.2]paracyclophanes and their

[3,3]dithioparacyclophane precursors in chloroform solution 132


(both in chloroform solutions) of compound 1c and 3c 150

Table 5.2 The electrochemical data of the polymers 3c 151

ix

List of Figures

Figures Page

Figure 1.1 Fig 1.1 A schematic representation of energy gap

in metal, insulator and semiconductor 6

Figure 1.2 Relationship between absorption, emission and

nonradiative vibration processes 8

Figure 1.3 The scheme for photoluminescence (PL) and

electroluminescence (EL) of conjugated polymers. 9

Figure 1.4 The Schematic diagram of the EL process 11

Figure 1.5 Synthesis of 9, 9-dialkyl-PF according to Yamamoto reaction 15

Figure 1.6 Synthesis of bicarbazole HTM materials 16

Figure 1.7 C-N bond coupling by Buchwald – Hartwig Reaction 17

Figure 1.8 Triphenylamine and thiophene units in HTM materials 18

Figure 1.9 3,6-disubstituted and N-substituted carbazole units in HTM materials 18

Figure 1.10 Star-shape thiophene and triphenylamine units in HTM materials 19

Figure 1.11 Diels-Alder reaction in the synthesis of HTM materials 20

Figure 1.12 Furan units in HTM materials 20

Figure 1.13 Some of the Organometallic ETL compounds 21

Figure 1.14 Oxadiazole and benzoimidazole units in ETL materials 22

Figure 1.15 Pyrimidine units in ELT materials 23

Figure 1.16 Triazene units in ETL materials 24

Figure 1.17 Silole units in ETL materials 25

Figure 1.18 Boride and per-fluorobenzene units in ETL materials 25

x

Figure 1.19 Thiophenesulfone, cyclooctatetraene and

diarylfluorene units in ETL material 26

Figure 1.20 Spirobifluorene units in blue light emission materials 28

Figure 1.21 Steric hindrance groups in blue light emission materials 29

Figure 1.22 Stilbene units in blue light emission materials 30

Figure 1.23 Tetra-phenyl substituted stilbene and coumarine structure units

in blue light emission materials 31

Figure 1.24 Oxadiazole units in blue light emission materials 31

Figure 1.25 Coumarin units in green light emission materials 32

Figure 1.26 Oxazolinone and pyrrole units in green light emission materials 33

Figure 1.27 Diphenylamine units in green light emission materials 34

Figure 1.28 Oxadiazole and nitrile units in green light emission materials 35

Figure 1.29 Bipolarity molecular design in green light emission materials 36

Figure 1.30 Isophorone and chromene units in red light emission materials 37

Figure 1.31 Polyacene units in red light emission materials 38

Figure 1.32 Neutral red core in red light emission materials 39

Figure 1.33 ETL and HTL structure units in red light emission materials 40

Figure 1.34 Maleimide and benzothiazazole units in red light emission materials 41

Figure 1.35 BCP and Oxadiazole units in hole blocking materials 43

Figure 1.36 Diazofluorenone, star-shape fluorene and aryl silane

units in hole blocking materials 44

Figure 1.37 Chapters work diagram 47

Figure 2.1 The sulfonium precursor route (SPR) 65

xi

Figure 2.2 The Gilch route 66

Figure 2.3 Ring-opening metathesis polymerization (ROMP) route 67

Figure 2.4 Protection and deprotection of -CH2Br group

on difluorenyl benzene ring 72

Figure 2.5 The thermalgravimetric analysis (TGA) of Polymer

P1 and P2 in a nitrogen atmosphere 74

Figure 2.6 The DSC traces of Polymer P1 and P2 75

Figure 2.7 The UV-vis absorption spectra and photoluminescence spectra

of Polymer P1 and P2 measured from their chloroform

solution at room temperature 76

Figure 2.8 Solvent effection on linear photoluminescence spectra of polymer P1 77

Figure 2.9 The cyclic voltammograms of P1 and P2 78

Figure 3.1 The thermalgravimetric analysis (TGA) of P1 & P2

in a nitrogen atmosphere 88

Figure 3.2 The DSC traces of P1 and P2 88

Figure 3.3 The UV-vis absorption spectra and photoluminescence spectrum

of Polymer P1 and P2 measured from their chloroform


Figure 3.4 The cyclic voltammograms of P1 and P2 91

Figure 4.1 Paracyclophane 96

Figure 4.2 Conjugated polymers including oligothiophene

xii

and [2.2]paracyclophane units 97

Figure 4.3 Main-chain-type [2.2]paracyclophane-containing

conjugated polymers 97

Figure 4.4 Dithia[3.3]paracyclophane-fluorene copolymers 99

Figure 4.5 The detection of Mn+ by dithia[3.3]paracyclophane-fluorene polymers 100

Figure 4.6 [2.2]Paracyclophane substitution patterns and ligands 100

Figure 4.7 Tetra- substituted Cyclophanes 102

Figure 4.8 Quadrupolar cyclophane systems 104

Figure 4.9 Cyclophane molecular structures used for charge transport 104

Figure 4.10 Normal ways to construct cyclophane derivatives structures 105

Figure 4.11 Retrosynthetic analysis of target tetrasubstituted [2.2]paracyclophane 106

Figure 4.12 Protection and deprotection of -CH2Br group on the benzene ring 115

Figure 4.13 Synthesis of [2.2]paracyclophanes from

[3.3]dithioparacyclophanes precursors 116

Figure 4.14 NMR spectrum of five target [2,2]paracyclophanes 119

Figure 4.15 The different protons on cyclophane core bridge -CH2 groups 120

Figure 4.16 MLDI-TOF mass spectrum of all final [2.2]paracyclophanes 123

Figure 4.17 The UV-vis absorption spectra and photoluminescence

spectra of DiS2F2F(11) and 2F2F(12) measured from

their chloroform solution at room temperature 124


of DiS2C2C(20) and 2C2C(21) measured from their chloroform


xiii


of DiS2F2C(22) and 2F2C(23) measured from their chloroform

solution at room temperature. 126


of DiS2F2T(28) and 2F2T(29) measured from their chloroform



of DiS2CT(30) and 2C2T(31) measured from their chloroform


Figure 4.22 The cyclic voltammograms of DiS2F2F(11) and 2F2F(12) 130

Figure 4.23 The cyclic voltammograms of DiS2C2C(20) and 2C2C(21) 130

Figure 4.24 The cyclic voltammograms of DiS2F2C(22) and 2F2C(23) 131

Figure 4.25 The cyclic voltammograms of DiS2F2T(28) and 2F2T(29) 131

Figure 4.26 The cyclic voltammograms of DiS2C2T(30) and 2C2T(31) 131

Figure 5.1 Structure of star-shaped oligomers with truxene and benzene core 140

Figure 5.2 Normal ways to synthesize di-R group substituted alkyne 143

Figure 5.3 Proposed mechanism of Cycloaromatization by using Co2(CO)8 144

Figure 5.4 1H and 13C spectra of target molecule 3c 145

Figure 5.5 MALDI-TOF mass spectrum of target molecule 3c 147

Figure 5.6 The thermalgravimetric analysis (TGA) of 3c 148

Figure 5.7 The DSC traces of 3c 149

xiv


of 3c and 1c measured from their chloroform solution

at room temperature 149

Figure 5.9 The cyclic voltammograms of 3c 151

xv

1

Chapter One

Introduction

1.1 Conjugated polymers

In 1977 Shirakawa’s group found that the conductivity of polyacetylene can be

increased significantly by doping it with various electron acceptors or electron donors.1

This discovery inspired an intensive investigation of highly conjugated organic polymers.

Many chemists and physicists considered the possibility of using organic polymers as

conductors. In the past three decades, various conjugated polymers, which have different

electrical,2 magnetic3 and optical properties4 owing to the substantial π-electron

delocalization along their backbones have been synthesized. Today, conjugated polymers

have been an active multidisciplinary research field not only because of their theoretically

interesting properties but also because of their technologically promising future.

1.1.1 Structure of conjugated polymer

Conjugated polymers can be characterized by the alteration of double (or triple) and

single bonds along the skeleton chain, and are indicative of a σ-bonded C-C backbone

with π- electrons delocalization. Such delocalization is the origin of semiconducting or

conducting properties of conjugated polymers. The combination of the properties of the σ

and π electrons allows these polymers to survive in a wide range of oxidation and

reduction states. These properties made them to be good candidates of electrochemical

insertion electrodes, high-conductivity/low-density metals, materials for non-linear optics

and as semiconductors.5-8 The chemical structures of some important conjugated

polymers are listed in Table1.1. 9

Table 1.1 Some Important Conjugated Polymers

Polymers Chemical Name Formula Bandgap(eV)

PA trans-polyacetylene n

1.5

PPP poly(p-phenylene) n

3.3

PF polyfluorene

R'R n

3.2

PPV poly(p-phenylenevinylene)

n

2.5

RO-PPV Poly(2,5-dialkoxy-p-phenylenevinylene)

n

OR

RO

2.2

PPE poly(p-phenylene

ethynylene) n

2.8

PT polythiophene S

Sn

2.0

P3AT poly(3-alkylthiophene) S

S

R

Rn

2.0

PPy polypyrrole NH n

3.1

PANI polyaniline HN

n

3.2

2

Polyacetylene (PA) is a prototypical example of this type of materials. Due to the

simplicity of its structure, it has been used as a model material for both theoretical and

experimental studies.10 The spin or charge-carrying segments of PA were viewed as

perturbations or as excitations in very long or infinite PA (CH)n chains. Such an

excitation can be described as a solitary wave of a fixed shape that can move along PA

chains. Such spin- or charge-density waves are classified as quasi- or pseudo- particles

and are called solitons.11 The Polymer PA can exist in several isomeric forms and the

trans-isomer, usually referred to as “trans-polyacetylene”, is a thermodynamically stable

isomer at room temperature.12

Poly(p-phenylene) and its derivatives(PPPs) have found considerable interest over the

past years since it acts an excellent organic conductor upon doping whereas neutral PPP

is a good insulator. A second major interest arises from the fact that PPP can be used as

the active component in blue light-emitting diodes (LEDs).13 Oligo(p-phenylene) have

played a dominant role as model compounds for PPPs in the study of physical

mechanisms related to intra- and inter-chain charge transport or distribution and

stabilization of charges and spins on π-conjugated chains. These mechanisms are of

special interest with regard to the potential application of PPP in rechargeable batteries.14

Poly(p-phenylenevinylene) and its derivatives (PPVs) are among the most extensively

studied systems since the first reported light-emitting devices(LEDs)15 using PPV as the

emission layer. The tremendous advantages in chemistry and physics of PPVs over recent

years have stimulated further interest in related types of structure such as poly(p-

phenyleneethylene) (PPE) polymers, which exhibit large photoluminescence efficiencies

3

both in the solid state as a consequent of their high degree of rigidity, and their extremely

stiff, linear backbones.16

Polythiophene (PT), polypyrrole (PPy) and their derivatives are among the most

widely studied types of π-conjugated polymers. In these polymers, N and S atoms

provide p orbitals which can couple with conjugated segments for continuous orbital

overlap. The N and S atoms are also necessary for these polymers to become electrically

conducting.12,2 In comparison to PA, PT and PPy provide higher environmental stability

and structural versatility. Polyanilines (PANI) and its oligomers have also attracted a

great deal of research interest towards their application in the field of conducting

polymers.12

Although the semiconducting behavior of conjugated polymers is easily understood

from the bonding, a polymer must satisfy two conditions for it to work as a

semiconductor.17,18 One is that the σ bonds should be much stronger than the π bonds so

that they can hold the molecule intact even when there are excited states, such as

electrons and holes, in the π bonds. These semiconductor excitations weaken the π bonds

and the molecule would split apart were it not for the σ bonds. The other requirement is

that π-orbitals on neighboring polymer molecules should overlap with each other so that

electrons and holes can move in three dimensions between molecules. Fortunately many

polymers satisfy these three requirements. Most conjugated polymers have

semiconductor band gaps of 1.5-3.0 eV, which means that they are ideal for

optoelectronic devices which emit light.

4

1.1.2 Bandgap of conjugated polymers

According to the band theory,19 the electrical properties of inorganic semiconductors

are determined by their electronic structures as the electrons moving within discrete

energy states which are called bands. For the conjugated polymers, their electronic and

optical properties are mainly determined by its π-electron system. In the ground state, the

π-electrons have a series of energetic levels that together form the π-bonds. The highest

energy π-electron level is referred to as the highest occupied molecular orbital (HOMO).

In the excited state, the π-electrons form the π* band. The lowest energy π*-electron level

is referred to as the lowest unoccupied molecular orbital (LUMO). The HOMO and

LUMO are known as the frontier orbitals. The energy difference between the highest-

occupied π band and the lowest unoccupied π* band is the π-π* energy band gap.

Electrons must have a certain energy to occupy a given band and need extra energy to be

excited enough to move from the valence band to the conduction band. In addition, the

bands should be partially filled in order to be electrically conducting because all empty

and fully occupied bands can not carry electricity. Owing to the presence of partially

filled energy bands, metals have high conductivities (Figure 1.1).20

Increasingenergy

Metal Insulator Semiconductor

Wide band gapNarrow band gap

Energy levels in conduction band

Energy levels in valence band

5

Fig 1.1 A schematic representation of energy gap in metal, insulator and semiconductor

When measured experimentally, the HOMO and LUMO all have a continuous

distribution. The top edge of the HOMO distribution corresponds to the ionization

potential (IP) of the molecule, and the bottom edge of the LUMO distribution

corresponds to the electron affinity (EA). The values of IP and EA are important

parameters for an OLED material because they determine the rate of hole and electron

injection.

Measurement of the energy of the HOMO of small molecules is done with ultraviolet

photoelectron spectroscopy (UPS). For polymeric materials which can not be thermally

deposited, electrochemical measurement of molecular electronic levels is required.21 This

technique is the cyclic voltammetry (CV). CV gives the values of the oxidation and

reduction potentials for a material in solution relative to a reference redox couple.

However, these values may not be equivalent to the true IP or EA. In solution, the

electronic structure of a molecule may be altered by the polarity of its surrounding. The

conformational freedom of a molecule in solution makes the addition or removal of an

electron easier than that for the condensed material. Then the energy gap between the

oxidation and reduction potentials measured electrochemically is usually slightly larger

than the optical energy gap for a conjugated polymer. By now, CV is still the best way

used as a relative measurement of the electronic levels for conjugated polymers.

Conjugated polymers generally have band gaps with in the range of 1.0-4.0 eV.22,23

The band gap of a conjugated polymer increases when its π-electrons become more

highly confined. In polymers where the wavefunctions are highly delocalized, the band

gap is largely determined by the degree of bond alternation. The key of obtaining small

6

band gap conjugated polymers is to design the chemical structure in such a way to

minimize the bond alternation. An example of this is polyisothianaphene(PITN), which

has a band gap of only 1.1 eV because it has an aromatic ring appended to its backbone

thiophene unit to reduce the bond alternation.23,24

PPP and PITN represent the extreme cases: PPP has a large band gap because its

excited state wavefunctions are localized to one repeat unit; PITN has a small band gap

because of its highly delocalized π-electrons and its minimal bond alternation. By tuning

the bond alternation and the torsion angles between rings in the polymer backbone, the

band gap of conjugated polymers can be tuned in fine increments from 1.0 eV to 4.0 eV.

1.1.3 Fluorescence from Conjugated Polymers

Conjugated polymers possess conjugated backbones, which allow π-electrons to be

delocalized extensively along the chain. The conjugated backbones in these polymers can

also be regarded as an extreme example of a long-chain chromophore. Most conjugated

polymers appear colored and show interesting photophysical phenomena, such as

photoconductivity,25 nonlinear optical properties (NLO) 5 and photoluminescence (PL).26

Figure 1.2 shows the relationship between absorption, emission and nonradiative

vibration processes.27

When a conjugated polymer is irradiated by light, photoexcitation of an electron from

the highest occupied molecular orbital (HOMO) (or ground state S0) to the lowest

unoccupied molecular orbital (LUMO) generates an excited state (S1) in which the

electron will lose the absorbed energy in the following ways: (1) Radiationless transitions,

such as internal conversion or intersystem crossing; (2) Emission of radiation, such as

7

fluorescence; (3) Photochemical reactions, such as rearrangements and dissociations. In

the excited state, some energy in excess of the lowest vibration energy level is rapidly

dissipated and the lowest vibration level of the excited singlet state is attained. If all of

this excess energy is not further dissipated by collisions, the electron returns to the

ground state with the emission of energy. This phenomenon is called fluorescence.

Consequently, much of the light energy absorbed by conjugated polymers may be lost by

processes other than fluorescence. Indeed, it is rare for conjugated polymers to emit all of

its absorbed energy as light. As shown in Fig 1.2, in most cases, the energy of emitted

light (hυe) is lower than that of the originally absorbed light (hυa). This difference

between absorbed and emitted light is termed as the Stokes shift.

S0

S1

S2

T1

T2

a fluorescence

b phosphorescence

a b

Singlet state Triplet state

intersystem

crossing

Radiation transition

Nonradiation transition

Vibration state

Electron state

Fig 1.2 Relationship between absorption, emission and nonradiative vibration processes

8

LUMO

HOMO

Interchainphotoexcitation

singlet excitonradiative decay

hvPL hv'

hv'

Electroninjection Recombination

Holeinjection

(-) polaron Singlet excitonradiative decay

(+) polaron

Cathode

Anode

EL

e-

e-

Fig. 1.3 The scheme for photoluminescence (PL) and electroluminescence (EL) of conjugated polymers The property of photoluminescence (PL) makes conjugated polymers suitable for the

application as active elements in polymer light-emitting diodes (PLEDs). In order to

understand the principles behind light emission in PLEDs, it is important to begin with

the simpler process of PL28 and realize the similarity between PL and

electroluminescence (EL)29 emission spectrum. The process of PL and EL are compared

in Figure 1.3.28 In PL, light is converted into visible light using an organic compound as

the active material whereas in EL, the organic compound converts an electric current into

visible light.30 Photoexcitation of an electron from the highest occupied molecular orbital

9

(HOMO) to the lowest unoccupied molecular orbital (LUMO) generates a single exciton

(a neutral excitation) which can decay radiatively with emission of light at a longer

wavelength (the Stocks shift) than that absorbed. Charged species (bipolarons) and triplet

excitons (detected by photo-induced absorption) provide the main channels for non-

radiative decay processes which can compete with and reduce efficiencies for radiative

decay of the singlet exciton.(Figure 1.4)31-33

Photoluminescence efficiency is an important property of photonic device. In polymers,

it is limited by two factors, one is the excimer formation and the other is existence of

quenching center.34 Excimer formation occurs when the backbones of neighboring chains

are very closely packed, which will result in a spectral red shift, spectral broadening and

inefficiency.35-37 The nature of quenching sites in polymers is not yet fully understood.

One type of quenching is the nonradiative recombination through carbonyl defects.38 A

small concentration of carbonyl defects can greatly reduce the efficiency of a polymer

because excitations migrate to find the defects, which have an energy level within the

band gap of polymer. Since the carbonyl defects form when conjugated polymers are

excited in the presence of oxygen, photonic devices are usually made in an inert

atmosphere and sealed in hermetic package.

10

Organicelectroluminescent

material

Polaronformation

Polaronformation

Electron/holerecombination

Exciton

25% S 75% T

Anode Cathode

Holeinjection

Electroninjection

Yield < 0.25 ( photoluminescence yield)

Fig 1.4 The Schematic diagram of the EL process33

The substituents on a conjugated polymer may have great effects on the fluorescence

property. Substituents which enhance the π-electron mobility will normally increase

fluorescence. A combination of electron-donating substituents with electron-withdrawing

substituents is also used to enhance fluorescence. PL can often be greatly enhanced by

increasing the intrinsic stiffness of a polymer backbone or by introducing large bulky side

groups to weaken intermolecular interaction.39 The close relationship between PL and EL

implies that increasing the ФFL will result in equal improvements in EL efficiency.

11

1.1.4 Application of Conjugated Polymers

Generally, the properties of the conjugated polymers can be mainly divided into two

parts. The one is focused on their reversible redox properties (i.e. electroactivity), while

the other is focused on their electrically conductive properties (i.e. conductivity). In the

first case, each application exploits the fact that the electrical and optical properties of

conjugated polymers depend on their level of oxidation or reduction in a controllable

manner. As a result, the conjugated polymers with this characteristic can be used as

electronic devices40, rechargeable batteries41, and drug release system. The combination

of electroactivity and reasonable stability in aqueous solution makes feasible the use of

selected conjugated polymers in the application of biomedical interest.42,43 Since the

conductivity of some conjugated polymers such as polyacetylene rise quite dramatically

with exposure to small amounts of “dopants”, they offer high sensitivity for detection of

these dopants.

In the area of sensors, considerable attention has also been directed towards

amperometric sensors, primarily for detection of glucose.44-46 It was also found that their

application as chemosensors,47 biosensors48 based on a variety of schemes including

conductormetric sensors49, potentiometric sensors, colorimetric sensors and fluorescent

sensors. In addition, conjugated polymers were also potential candidates as electrically

conducting textiles by incorporation of conductive fillers50 and candidates as artificial

muscles based on transition change caused dimensional changes.51 The use of conjugated

polymers in industrial separation is gaining increased popularity due to the cost and

energy conservation advantage. Electronically conducting polymers such as

polymethylpyrrole and polyaniline are promising materials for industrial gas separation.

12

On the other hand, the application simply takes advantages of electrical conductivity of

doped conjugated polymers, which makes them attractive alternatives for certain

materials currently used in microelectronics. The conductivity of these materials can be

tuned by chemical manipulation of the polymer backbone, by the nature of the dopant, by

the degree of doping, and by blending with other polymers. In addition, they offer

advantages such as light-weight, operability and flexibility which entitle them potential

application ranging from the device level to the final electronic products. It is reported

that polyaniline52, polyacetylene53 and polypyrrole54 can be widely used as conducting

resists in the lithographic applications, polyaniline as the materials for shielding

electromagnetic radiation and reducing or eliminating electromagnetic interference.55-57

One of the most advanced application of conducting polymers is their use as active

materials in photoelectronic devices, such as light-emitting diodes58, light-emitting

electrochemical cells,59,60 photodiodes61-63, field effect transitors,64-70, polymer rigid

triodes71, optocouplers72 and laser diodes73 etc. Some of these polymer-based devices

have reached performance levels comparable to or even better than those of their

inorganic counterparts. In addition, conjugated polymers can also be used for applications

such as electrostatic shielding, non-linear optics74,75, electrochromic windows76 and

photodetectors.77,78

1.2 Polyfluorene as Light Emitting Polymer

Alkylsubstituted polyfluorenes have emerged as a very attractive class of conjugated

polymers, especially for display applications, owing to their pure blue and efficient

electroluminescence with a high charge-carrier mobility and good processability. The

13

availability of specific and highly regioselective coupling reactions provides a rich

variety of tailored polyfluorene-type polymers and copolymers.

First attempts to synthesize soluble, processable poly(2,7-fluorene)s (PFs) via an

attachment of soluble substituents in 9-position of the fluorene core were published in

1989 by Yoshino and co-workers. They coupled 9, 9-dihexylfluorene79 oxidatively with

FeCl3 and obtained low molecular weight poly(9,9-dihexylfluorene) (PF6, Mn up to 5000,

Pn= 9-13). This oxidative coupling is not strictly regioselective, as structural defects are

created besides “regular” 2, 7-linkages.

The enormous progress in the availability of efficient and strictly regioselective

transition metal-catalyzed aryl-aryl-couplings has paved the way for the synthesis of high

molecular weight, structurally well-defined PF derivatives. Especially reductive aryl-aryl-

couplings of dihaloaryls according to Yamamoto reaction, aryl-aryl cross-couplings of

aryldiboronic acids (esters) and dihaloaryls according to Suzuki reaction or distannylaryls

and dihaloaryls according to Stille reaction have been successfully applied.

The first transition-metal catalyzed coupling of 2,7-dibromo-9,9-dialkylfluorenes

with NiII salt/zinc was described by Pei and Yang (Uniax Corp.) in 1996.80 Later on, a

research group at DOW Chemical Corp. 81 as well as Leclerc and co-workers82 published

the synthesis of 9,9-dialkyl-PFs following the Suzuki-type cross-coupling of 9,9-

dialkylfluorene-2,7-bisboronic acid or ester and 2,7-dibromo-9,9-dialkylfluorene

monomers.

Since the Suzuki-type coupling provides PFs with a maximum Mn of several 10000,

the Yamamoto-type coupling can lead to very high molecular PFs with a Mn of up to 200

000 (Pn: up to 500).83 The main prerequisite for reaching such high molecular weights is,

14

however, the use of carefully purified monomers and the application of optimized

reaction conditions. On the lab scale (up to 10 g batches), the application of Ni(COD)2 as

reductive transition metal-based coupling agent is very favorable (Figure 1.5 ).

Br Br

R R R R n

Ni(COD)2.

Fig 1.5 Synthesis of 9, 9-dialkyl-PF according to Yamamoto reaction

1.3 Organic Light Emitting Diodes (OLED)

OLED is a multiple layers thin film device. In an outside electric field, the emission

layer can form excited state and release energy by giving out light. This process is

electroluminescence (EL). The complicated device structure and different layers

materials requirements need the contribution of careful molecular design and synthesis

work.84 The properties of different devices layers and their synthesis works are presented

as follows. These summary are very useful not only in OLED but also in application of

other conjugated polymers.

1.3.1 Hole transporting material, HTM

In an OLED device, the hole transporting material is in the middle of anode and

emitting layer. It will help the hole transportation and injection into the emitting layer.

HOMO energy level of hole transporting materials should be near the potential of the

anode and be higher than the emitting layer. Most of the normal HTM materials are

triarylamine. According to the central core part of triarylamine, there are biphenyl,

15

starburst and spiro kinds of HTM. Copper catalyzed Ullmann coupling reaction is often

used in the synthesis of bicarbazole HTM materials(Figure 1.6).85-87

HN

N

I I

1,10-phenanthrolineCuCl, KOH, toluene,

85%

N

TPD

1

NH

HN

I

K2CO3, Cu2SO4

Decane

N

N

2

Fig 1.6 Synthesis of bicarbazole HTM materials

Palladium catalyzed Buchwald – Hartwig Reaction was widely used in the synthesis of

triarylamine to form C-N bond (Figure 1.7). 88-94

The key of the spiro HTM materials synthesis is the construction of the central core

which was synthesized from the bromides of the spiro compounds.95,96

N NNH

BrBr

Pd(OAc)2, P(t-Bu)3NaO-t-Bu, o-Xylene

92%

3

16

BrBr

Br Br

HN

NPh2Ph2N

Ph2N NPh2Pd(OAc)2, P(o-CH3Ph)3

NaO-t-Bu, toluene

4

BrBr

O

HN

Pd(OAc)2, P(t-Bu)3

NaO-t-Bu, Xylene

NPh2Ph2N

O

5

t-But-Bu1.

2. MeSO3H, AcOH

NPh2Ph2NLi

6

Fig 1.7 C-N bond coupling by Buchwald – Hartwig Reaction

The starburst HTL materials have high potential in the future application.97,98 With an

electron rich structure, thiophene compounds can also be used as HTL materials(Figure

1.8).

99

17

N NN

I

I

I

HN

N

N

Cu, KOH

7

S

S

Ph

Br

Ph

Br

HN

Ar

Pd(OAc)2, P(t-Bu)3NaO-t-Bu, toluene

S

S

Ph

N

Ph

NAr

Ar

8

Fig 1.8 Triphenylamine and thiophene units in HTM materials

The bromination reaction is easy to be processed on the 3, 6 position of carbazole.

From this carbazole dibromide, HTL materials with emitting properties can be obtained

by transition metal catalyzed C-N bond coupling reaction (Figure 1.9).100,101

N

Br Br

N

N

NNH

R

R R

Pd(dba)2, P(t-Bu)3NaO-t-Bu, toluene

9

18

NH

BrBr

CH3

H3C

N

CH3

H3C

N

Pd(OAc)2, P(t-Bu)3NaO-t-Bu, Xylene

10

Fig 1.9 3,6-disubstituted and N-substituted carbazole units in HTM materials

Some HTL materials have higher triplet state energy level, which can be used as the

phosphorescence emitting layer.102

Another synthetic method choose using metal substituents compounds to react with the

halogen core compounds.(For example, use Stille reaction to complete the synthesis of

starburst compounds).103

The homologue compounds with a thiophene core can be obtained by Kumada

coupling reaction.104,105 Triarylamines can also be obtained by aromatic electrophilic

substitution reaction (Figure 1.10).106

BrBr

BrBr

Br

Br

SBu3Sn N

Ph

Ph

S

NPh

Ph

S

N

PhPh

S N

Ph

PhS

N Ph

Ph

S

N

PhPh

SN

Ph

Ph

Pd(PPh3)2Cl2

11

19

N N NMgBr

SBr Brn S

n

n=1-4

12

BrBr

O

N

N

BrBr

NMeSO3H, 1700C

13

Fig 1.10 Star-shape thiophene and triphenylamine units in HTM materials

A high thermal stability HTL compounds can be obtained by Diels-Alder reaction

(Figure 1.11).107 Heterocycle compounds with high electron density have hole

transporting properties. The homologue compounds of thiophene and furan are often used

as HTL materials (Figure 1.12).108,109

O O O

O ON

N

N

H2N

Benzophenone1,2,4-trichlorobenzene

14

Fig 1.11 Diels-Alder reaction in the synthesis of HTM materials

20

SS

1. BuLi

2.

3. TFA

CHOOHCOO

15

Fig 1.12 Furan units in HTM materials

1.3.2 Electron transporting material (ETL)

Electron transporting materials (ETL) have higher electron affinity (low LUMO

energy level). ELT makes it easy for the electrons to be injected from cathode and match

the LUMO level of emitting layer, thus increases the efficiency of electron injection. In

addition, ETL needs higher ionization energy (low HOMO energy level) to limit holes in

the surface of emitting layer and ETL layer. For these properties, electron-withdrawing

groups or metal ion will be introduced into the synthesized ETL compounds. Normally

there are two kinds of ETL materials.

1.3.2.1 Organometallic ETL compounds

Some of the Organometallic ETL compounds are shown in Figure 1.13.

21

N

N

NO

O

O

Al

N

O N

OBe

O

NZn

N

O NO

NO

Al OH

N NNNZn

O

O

O

NN

O

N N

O

OZn

O

O

OO

O

O

Al

16 17 18 19

20 21 22

Fig 1.13 Some of the Organometallic ETL compounds

1, 3, 4-Oxadiazole is often used as the coordinating group. It can be synthesized from

hydrazine by cyclic condensation reaction.110-114 The coordinating group of

benzoimidazole is synthesized by dehydration-condensation reaction in high temperature

(Figure 1.14).115

O

N NHO

O

NH

HN

O OH

SOCl2

.

23

O

Cl

RN

N

NHN

O

N NR+

Pyridine

24

22

O OH

OCH3NH

NH2

N N

OH

1,2-dichlorobenzene

170-2200C+

25

Fig. 1.14 Oxadiazole and benzoimidazole units in ETL materials

1.3.2.2 Non-Organometallic ETL Compounds

Organic ETL compounds have high electron affinity aromatic heterocycles. For

example, in compound TAZ, 1, 2, 4- triazole can be synthesized from aniline and

hydrazine by a dehydration-condensation reaction in the presence of PCl3.116

The pyrimidine cycle has very good electron affinity. The conjugated compounds with

pyrimidine cycle can be used as ETL materials. They can be synthesized by Suzuki

coupling reaction with the constructed pyrimidine cycles117 or by using ring closing

reaction to form the pyrimidine cycles (Fig 1.15 ).118

O

NH

HN

O

NH2

N

N NPCl3

26

N

NIBr

R(HO)2B N

NBr R

Pd(PPh3)4, Na2CO3

Toluene, reflux

OC8H17

C8H17O

B(OH)2(HO)2B

Pd(PPh3)4, P(t-Bu)3,Na2CO3

Toluene, reflux

23

OC8H17

C8H17O

N

NR

N

NR

.

27

N

NN

NMe2N

Me2N

N

N

NH2

NH2

Pyridine

.

28

Fig 1.15 Pyrimidine units in ELT materials

The organic compounds with triazene cores also have good electron transporting

ability. These triazine compounds can be synthesized by imine and benzamidine ring-

closing reactions,119 lithium reagent and 2, 4, 6-trichlorotriazene substitution reactions

and CF3SO3H catalyzed trimerization reactions. 120 121

FN

NH2

NHN

N

NF

2

29

24

BrN

N NN

Cl

ClCl N N

N

NN

N

Et

Et

1. n-BuLi, THF, -400C

2.

Et

Et

Et

Et

Et Et

.

30

CNBr N N

N

N

N

N

N N

N

NN

N

N N

N

BrBr

Br

CF3SO3HNH

NN

CuSO4, K2CO3

31

Fig 1.16 Triazene units in ETL materials

Some special structure compounds (such as silole cycle compounds) have very good

properties as ETL materials. Silole cycle compounds have special orbital symmetry. The

σ*(Si)-π(C) action can lower LUMO energy level and is propitious for electron

injection.

Silole cycle compounds were synthesized by a reduction cyclization reaction of

dialkynylsilane derivatives first and then extended the molecular length by Pd catalyzed

coupling reaction. Intramolecular C-Si bond forming reaction was also used in silole

cycle compounds reduction cyclization reaction (Figure 1.17).

122,123

124

125

25

Triaryl boride compounds can also be used as ETL materials. Direct organometallic

substitution, such as addition reaction of aryllithium reagent and diaryl halogenoborate

was chosen for the synthesis.126,127

Fluorine atom has high electronegativity and can be used as substitution group of

aromatic conjugated compounds. These compounds can be synthesized by Ullmann

coupling reaction. They are effective ETL materials (Figure 1.18).128

Si

Me MeS

Me Me

ZnClClZn

N N

SMe Me

N N

NN

Br1. LiNaph(4 equiv.),

THF

2. [ZnCl2(t-men)](4 equiv.) Pd(PPh3)2Cl2

32

SiMe2(OEt) SiMe2(OEt)

(EtO)Me2Si (EtO)Me2Si

SiSi

Si Si

Me Me

Me Me

Me Me

Me Me

1. LiNaph(8 equiv), THF

2. I2 (8 equiv)

33

Fig 1.17 Silole units in ETL materials

S SSLiLi

B

S SSBB

F

34

26

F F

F F

F4

Br Br

F F

F F

F

F F

F F4

F F

F F

F Cu

.

35

Fig 1.18 Boride and per-fluorobenzene units in ETL materials

Oxidizing the sulphur atom in thiophene can change the electron rich properties of

thiophene to electron deficient. The conjugated compounds, which were constructed

from oxidizing part of thiophene by coupling reaction, can also be used as ETL

materials.129,130

The normal conjugated hydrocarbons have no electron transporting ability. But

cyclooctatetraene can be used as ETL material. It was synthesized by Ru catalyzed

cyclotetramerization reaction.131

9,9- Diaryl trifluorene compounds (TDAF) have been proved to have high efficiency

in electron transporting.132 Suzuki-coupling reaction was used in the synthesis route.

These pure hydrocarbons can be used as ETL materials in the OLED devices (Figure

1.19).133

S

C6H13 C6H13

O O

Bu3Sn

S

C6H13 C6H13

Br

O O

Br

Pd(AsPh3)4Toluene

.

36

27

(Ph3P)3Ru(CO)H2

Toluenen, Styrene

a

37

Ar Ar Ar ArAr Ar

BBO

OO

OAr Ar

Ar Ar

Br X

Pd(PPh3)4, P(t-Bu)3

Na2CO3, Toluene, reflux

38

Fig 1.19 Thiophenesulfone, cyclooctatetraene and diarylfluorene units in ETL materials

1.3.3 Blue light emitting materials

Blue light has shorter wavelength and higher energy and can be changed to green and

red light by energy transfer. High efficient blue light emitting materials play a very

important role in full color OLED display panel. Pure aromatic hydrocarbons such as

BTP have very good blue light emitting properties.134 BTP can be synthesized by Pd

catalyzed ring-opening dimerization reaction(Figure 1.20).135

The blue light emitting compounds with spirobifluorene backbones have higher

fluorescence quantum yield because of their rigid and co-planar structure. The synthesis

route started from constructing of spirobifluorene core. After halogenation reaction of the

spirobifluorene cores, the conjugated length of the molecules can be extended by

transition metal catalyzed coupling reaction.136 Suzuki coupling reactions were often used

in these reactions (Figure 1.20).137-139

28

O

HSiCl3

Pd(dba)2, Zn, Toluene .

39

.

40

.BBO

O O

O

Br

+

Pd(PPh3)4, P(t-Bu)3

Na2CO3, Toluene, reflux

.

41

O

O

OBB

O Pd(PPh3)4, P(t-Bu)3

Na2CO3, Toluene, reflux+

N

NBr t-Bu

N

N

N

Nt-But-Bu

42

29

Toluene, aliquat 336

Pd(PPh3)4, K2CO3

BO

O

+B

O

OBr .

43

Fig. 1.20 Spirobifluorene units in blue light emission materials

The great steric hindrance of spirobifluorene avoids intermolecular stacking. It can be

used as terminal group. Spirobifluorene140 and other special steric hindrance groups141,142

were introduced into the 9, 10-position of anthracene. The obtained blue light emitting

material has very good device properties (Figure 1.21).

+Br

(HO)2B B(OH)2

Pd(PPh3)4.

K2CO3, THF/H2O

44

30

O

O

Br Li OH

HO

Br

Br

NH

NN

Et2O,-780C

KI/NaHPO2

HOAc, reflux

Pd2(dba)3, P(t-Bu)3, NaO(t-Bu)

Br

Br

45

Fig. 1.21 Steric hindrance groups in blue light emission materials

The stilbene kind compounds such as DPVBi(46)143 have good blue light emitting

device efficiency. Their silicon substitution compounds also emit blue light. The key

synthesis reaction was hydrosilylation which formed C-Si bond.144,145

Compound XTPS (47) was found to have good blue light emission properties. Its

terminal groups were constructed by Diels-Alder reaction. Its C=C bonds were

constructed by Horner-Wadsworth-Emmons reaction (Figure 1.22).146

31

SiMe2HHMe2Si

OC4H9

C4H9O

H

RhCl(PPh3)3

SiSi

OC4H9

C4H9O

Me

Me

Me

Me

46

47

Fig. 1.22 Stilbene units in blue light emission materials

Some heterocycle conjugated compounds have good blue light emitting quantum

yields and can be used as the emitting layer in OLED device. Compound MeCl(49) wit

e C-N bonds then

llowed the BBr3 deprotection and cyclic condensation (Figure 1.23).

h

a coumarin backbone, was synthesized by Ullmann reaction to form th

fo

Ph3Si(PhTPAOXD)(compound 50) has a electron deficient 1, 3, 4-oxadiazole ring and

electron rich triarylamine groups.147 This makes it possible for the charge transfer in the

molecule. This dipolar molecule design keeps a balance in the electrons and holes

combination. The key step of the synthesis is the cyclization reaction of oxadiazole

(Figure 1.24)

32

O

Ph Ph

PhPh

CO2HPh Ph

PhPh

CO2H

Ph Ph

PhPh

1. LAH

2. CCl4, PPh3

3

P(OEt)2

O

N

CHO

PhBr

1. NaH

2.

3. P(OEt)

NPh Ph

Ph

Ph

48

MeO

NH2

Me

IN

OMe

N O O

Cu, K2CO3, 18-crown-6,1,2-dichlorobenzene

1. BBr3

2. Acetoacetic acid70% Sulphuric acid

49

Fig 1.23 Tetra-phenyl substituted stilbene and coumarin structure units in blue light emission materials

CH3Br COOHPh3Si

N

NHN N

NN

1. n-BuLi

3. KMnO4

1. SOCl2

2. Ph3SiCl

O

N NPh3Si

2.

.

50

Fig 1.24 Oxadiazole units in blue light emission materials

33

1

route.

.3.4 Green light emitting materials

Coumarin serial compounds have high green light emitting quantum yields. Many

derivatives were synthesized to improve the emitting efficiency. Compound 51 have

very good green light emitting efficiency because of the introduction of rigid julolidine

structure and four methyl groups’ steric hindrance.148 The construction of core cycle

structure in coumarin serial compounds was very important in the whole synthesis

149 150 In the synthesis of compound 52, coumarin ring was constructed first and

ine to obtain the heterocycle part (Figure 1.25). then reacted with 1, 2-phenyldiam

N OH

O

HN

SEtOO

N O

N

Spiperidine

O .

51

N N O ON O O

O

OEtH N2

H2N

HN

N

OHO

OEt

EtO OEtO

52

Fig 1.25 Coumarin units in green light emission materials

Many structures of organic chromophores can be learnt from nature simulation. For

example, the oxazolone part derived from green fluorescent protein aequorea was very

efficient in green light emission. 151

34

The compounds with pyrrole ring core structure can work as OLED green light

dopants.152 They can be synthesized by introducing pyrrole-thiophene rings first, then

introducing aldehyde and electron-withdrawing groups in the C=C bond coupling

reactions. N, N’-diethylquinacridone is also a good green dye in OLED devices (Figure

1.26).153,154

NO

O

NH

OOH

O

O

HNaOAc, acetic anhydride

.

53

NSS

OMe

NSS

OMe

CHO

NSS

OMe

S

Me

O

O

MeS

MeS S

O

MeO

1. n-BuLi, -780C

2. DMFn-BuLi, TMSCl,

0THF, -78 C

54

HO2C

PhHN

NHPh

N

NO

H O

H

N

NO

Et O

Et

CO2H

H3PO4

H2O

EtBr

55

Fig 1.26 Oxazolinone and pyrrole units in green light emission materials

35

Combining the high fluorescence quantum yield of anthracene and hole transporting

properties of triarylamine compounds, α-NPA is a good candidate of green light emission

materials.155 It can be synthesized by Pd catalyzed C-N bond coupling reaction. The same

synthetic methods can also be used in the synthesis of hole transporting new green light

emitting materials with dibenzochrysene part (Figure 1.27).96,156

Br Br N N

NH

Pd(OAc)2, P(t-Bu)3NaO(t-Bu), o-Xylene

.

56

O

NPh2Ph2N

O

Ph2N NPh2

Ph2N

NPh2

NPh2Ph2N

Ph2N NPh2

P(OEt)3 H

57

Fig 1.27 Diphenylamine units in green light emission materials

To keep a balance in electron-hole recombination, some special structure parts were

introduced into the chromophores. In a dipolar molecule with a carbazole core, its

emission efficiency was highly improved when oxadiazole cycle was introduced(Figure

1.28).157,158

36

NEt

Br

NEt

PhHN NHPh

PhN NHPhPd(dba)2, P(t-Bu)3NaO-(t-Bu), Toluene

O

N NBr

C4H9 C4H9

NEt

PhN PhNO

N N

C4H9 C4H9

Pd(dba)2, P(t-Bu)3NaO-(t-Bu), Toluene

58

NEt

Br

NEt

CNBrCN

NEt

NEt

CNN

CuCN

THF

NBS

DMF

NHP

Pd(dba)2, P(t-Bu)3NaO-(t-Bu), Toluene

h

.

59

Fig 1.28 Oxadiazole and nitrile units in green light emission materials

The synthesis method of dipolar molecule design can also be used in the other colors

light emitting materials. For the synthesis of compound 61,159 the key step is Cu

catalyzed Ullmann reaction. Thiophene ring was introduced by Suzuki reaction. Lithium

reagent was used to do the deprotonation. In the final, borane reagent was used to

t molecule (Figure 1.29). complete the addition reaction to obtain the targe

37

Me Me

I

MeMe

NH2 N

MeMe

Cu, K2CO3,18-Crown-6trimethyl benzene

1. NBS

2. Pd(PPh3)4,THF, K2CO3

S B(OH)2

.

B

F

Me

MeN

MeMe

SB

Me

MeN

MeMe

1. n-BuLi

2.

S

60

Fig 1.29 Bipolarity molecular design in green light emission materials

1.3.5 Red light emitting materials

In red light emitting materials design, the emitting light wavelength can be extended to

red light area by using intramolecular energy transfer. These Donor-Accepter (D-A) kind

molecules have very strong molecular dipole. The strong interaction of these pure

molecules as emitting layer materials often resulted in fluorescence quenching. Thus

these D-A kind molecules were often used as dopants in OLED devices. In these

materials, DCM(61)160,161 and DCJTB(63)162,163 can be obtained by condensation reaction

of amino benzaldehyde derivatives electron-donors and electron accepter parts. Changing

the electron accepters to be isophorone would avoid by-products forming and a series of

red light emitting materials with good properties can be synthesized (Figure 1.30).164-166

38

N

O

CNNC

61

.

N

CNNC

62

.

.

O

CNNCN

OH

HNN

O

NC CN

..

, CH3CN

63

.O

NC CN

N

NC CN

NC CN

Ac O2

NO

H

HN , CH3CN

64

OH

O

OH

O O

O

O

EtOAc

EtON

HOAc

HCl

NC

a

CN

Ac O2

O

NC CN

NO

HNO

NCCN

.

piperidine, CH3CN

65

Fig 1.30 Isophorone and chromene units in red light emission materials

39

In pure hydrocarbons, Polyacenes can be used as red light emitting dye dopant because

of their good molecular conjugation.167 In these compounds, 6, 13-diphenylpentacene

(DPP)(66) can be synthesized by addition reaction of Grignard reagents and quinone

compounds.168 Rubrene(67) can be synthesized by cyclization reaction of propargyl

chloride and quinoline (Figure 1.31).169,170 High fluorescence red light materials can also

be obtained by reaction of neutral red and naphthalic anhydride (Figure 1.32).171

O

O MgBr HO

OH

PhPh

KI

HOAC

66

Cl

Ph Ph

Quinoline

67

O

O

NEt

EtLi

NEtEt

NEt Et

NEtEt

NEt Et

HO

HO

SnCl2

68

40

Fig 1.31 Polyacene units in red light emission materials

N

N CH3

NH2NH3C

CH3

N

N CH3

NH3C

CH3

O OO

N

O

OQuinoline

.

69

Fig 1.32 Neutral red core in red light emission materials

In red light materials design, introducing the structure parts with electron-transporting

or hole transporting properties can balance the electrons and holes recombination

efficiency.

These materials pure thin films can be used directly as emitting layers in devices.172

Benzo- α – aceanthrylene derivatives, with properties of polycyclic aromatics and

triarylamine groups hole-transporting, can be used as pure emitting layer. The key

synthesis step was addition and dehydration reaction of anthroquinone. The final product

can be obtained by Pd catalyzed C-N bond coupling reaction and cyclization reaction in

the meantime.173

Arylamino fumaronitrile, with two CN groups in the C=C double bond and triaryl

amino group as electron-donor, is a good red light material. It can be obtained by

dimerization of phenylacetonitrile and Pd catalyzed reaction to introduce aromatic amine

groups (Figure 1.33).174

41

IMeO

HN

N

OMe OMe

N

CHO

Cu, K2CO3

1. POCl3, DMF

2. NaOH

MeOCNNC NC

NaOMeCN

OMe

70

Br

O

O

Cl

Br

Br

HO

OH

Cl Cl

Br

NH NN

Br Li KI

NaH2PO2HOAc

.

71

Pd(OAC) , P(t-Bu)2 3

Cs2CO3, Toluene

72

Fig 1.33 ETL and HTL structure units in red light emission materials

A series of single layer red light emitting materials were obtained by using maleimide

as electron-accepter structure parts and introducing aromatic amino groups as electron-

donors (Figure 1.34).175-178

42

Br

CN

HNO O

Br Br

NO O

Br Br

CH3

NH

1. I2, THF,NaOMe/MeOH

2. 3% HCl, THF

KO(t-Bu), CH3I,DMF

NCH3

O O

Pd(OAC)2, P(t-Bu)3NaO(t-Bu), Xylene

N N

73

NO O

Br Br

CH3N

CH3

NO OCH3

CH3

N N

1. MeMgCl

2.

.

74

.

NS

N

BrBrBu3Sn

NS

N

Br

N

S NBu3Sn

Pd(PPh3)2Cl2, DMF Pd(PPh3)2Cl2, DMF

N

S

NS

N

N

75

A new D-A kind materia

Fig 1.34 Maleimide and benzothiadiazole units in red light emission materials

l can also be used as pure single emitting layer. It combined

the high electron affinity of benzothiadiazole and electron rich property of thiophene and

43

triarylamine. The Pd catalyzed Stille reaction was the key step in synthesis (Figure

1.34).179

1.3.6 Hole Blocking materials

A charge carrier blocking layer was introduced in the device design for an effective

controlling of excitons combination area. Now hole blocking materials is common used

as blocking layer. To keep the holes effectively before the electron-transfer layer, hole

blocking materials should have lower HOMO energy level. High electron affinity groups

such as aromatic heterocycles or fluorinated organic conjugated compounds were often

used in hole blocking materials design. A good hole blocking material can have good

electron-transfer and electron-injection properties simultaneously. BCP180 is a common

hole blocking material. It was synthesized by addition reaction of quinoline and phenyl

propenyl ketone and H3ASO4 catalyzed cyclization dehydration reaction.181

1,3,4-oxadiazole is a high electron deficient heterocycle. It was introduced into

conjugated system to be electron-transfer material. An effective hole blocking material

can be obtained by connecting 1, 3, 4-oxadiazole with another electron-deficient structure

part such as pyridine (Figure 1.35).182

NNH2 O

N N

76

1. 85% H3PO4, 1200C

2. H3AsO4

.

44

N

O

OH

O

HO N

O

NHNH2

O

H2NHN

O1. MeOH/H2SO4 t-Bu

Cl

N

O

NHNH

O

HNHNO O

t-Bu t-Bu

N

O

N N

O

N Nt-Bu t-Bu

PDPyDP

POCl3

2. EtOH/N2H4 H2O Pyridine

77

Fig 1.35 BCP and Oxadiazole units in hole blocking materials

Dipyridine derivatives with coplanarity have good electron-transfer and hole blocking

properties.183 It can be synthesized by strong Friedel-Craft reaction of 4, 5-diazafluoren-

9-one and anisole derivatives.184,185

Conjugated compounds with shorter alkyl chains can also be used as good hole

blocking materials. For example, TFPB, its star-shaped structure can effectively limit the

whole molecule conjugation extension and lower the HOMO energy. Suzuki reaction was

the key step in the TFPB synthesis.186

Another synthesis design used σ bonds as blocking parts of molecular conjugation

extension. Si atom was used as the blocking part in DPSVB molecule to confine the

molecular conjugation length in the central conjugated cell.187 It can be synthesized by

Nickel catalyzed coupling reaction of thioacetal and silicon containing Grignard reaction

(Figure 1.36).188

45

N N N N

OMeO

N N

MeO OMe

KMnO4

KOH H2SO4, 650C.

78

I

II

B(OH)2

Pd(PPh3)4,THF, K2CO3

79

Me

S

SS

S

Si

Si

MeNiCl2(PP

Ph2MeCH2MgCl

h3)2

80

materials

1.4 Project objectives

Conjugated organic compounds play a primary role in the development of a new

generation of opt

Fig. 1.36 Diazofluorenone, star-shape fluorene and aryl silane units in hole blocking

ical and electronic materials. Our research focus on the synthesis of

ovel fluorene based polymers and oligomers. Novel structure units and novel synthesis

methodology play important roles in our research work.

n

46

Figure 1.37 Chapters work diagram

Figure 1.38 is the diagram of our four chapters work. In this diagram, Diaryl

ne is our key precursor. From this compound, we can easy to obtain

PPV compounds (Chapter 2). The novel fulvalenes polymers

dibromomethyl benze

the diaryl substituted

(Chapter 3) were introduced to explore the bistricyclic aromatic units’ effect in polymer

properties. The tetra-aryl substituted cyclophane compounds (Chapter 4) can also be

obtained by using our key precursor. Hexaarylbenzene compounds were synthesized to

47

study their properties and relations with the structure. The more details of the work will

be explained in following paragraphs.

Polymer light-emitting devices (PLEDs) are the most intensely investigated area for

the application of PPV derivatives. PPV provides excellent hole-transporting layers189 in

PLEDs in addition to be the active emissive layer. With precisely chemical modifications

and device engineering, PPVs give colors which cover the entire visible spectrum of

colors with good efficiencies under a bias of only a few volts. In addition, the excellent

film-forming properties of PPVs suggest that a large area display can be fabricated from

these polymer materials.

PPV compounds have a good planarity due to their conjugated alkene skeleton. This

planarity is important for charge separating and transfer. But aggregation was also caused

by the good planarity. This aggregation will deduce the quantum yield and solubility of

polymers. In our work, we hope to introduce huge steric hindrance chromophores as side

chains into the PPV polymers. These side chains will combine their own properties

together with the PPV main chain and adjust the properties (such as HOMO, LUMO

ic hindrance caused by these side chains can be a

through the interring double bond and capable of generating two separate aromatic

energy level) of polymers. The ster

favorite factor to decrease the aggregation and increase the photoluminescence efficiency

of polymers. In the work of PPV derivatives polymers synthesis, two chromophore side

chains PPV compounds were designed. By our knowledge, this is the first time to

synthesize these di-chromophore side chains PPV compounds. We hope to explore these

novel derivatives properties and applications.

Fulvalenes are molecules with two unsaturated ring systems showing cross conjugation

48

moieties. By our knowledge, no report has been made on tetrabenzofulvalene’s usage in

materials. In order to investigate the effect of bistricyclic aromatic units on the polymer

f [2, 2] parcyclophane190 was used in almost all of the works to

macromolecules that consist of linear

backbone, two novel tetrabenzofulvalene units containing polymers were designed. We

hope to explore how the Tetrabenzo[5.5]fulvalene make an effect on whole polymer

properties and find the potential application of these polymers.

Cyclophane, in which two benzene rings are close to each other and cofacial, is

attractive in its structure, reactivity and physical properties. Cyclophanes have optically,

electrically, and topologically intriguing features.

Direct bromination o

obtain the desired cyclophane bromides from which functional groups can be attached on.

The yield of this method is very low and has almost no possibility to have different

substituents on one cyclophane core. In our work, novel tetra-substituted

[2.2]paracyclophanes with different chromophores were designed. We hope to construct

cyclophane core by using coupling reaction. By this method, we can attach the wanted

functional groups on the two aromatic benzene rings first. Then we use two same or

different substituted benzene rings to form the cyclophane core. This gives us wider

choice to introduce different functional groups on the cyclophane cores. This freely

modification makes the synthesis route very useful to obtain different [2.2]

paracyclophanes derivatives which can be used in different applications areas such as

asymmetric reaction, OLED and NLO materials.

Star-shaped oligomers are branched

molecular arms joined together by a central core191. Star-shaped oligomers are unique in

the sense that they combine the properties of the arms with that of the central core (which

49

can have one to three dimensional characters) and this will bring new interesting

optoelectronic and morphological properties to the system. Recently, hexaarylbenzene

have attracted immerse interest in the materials community; aryl “arms” such as

azulene192, pyrene193 and ferrocene194 have been attached and these systems shows more

superior properties than their trisubstituted star-shaped analogue. In our work, we try to

ficiency and their ease of

synthesize high steric hindrance hexafluorenylated benzene. We thus decide to tap on

the potential of such “double” star-shaped system, using “fluorenyl” units as the arms as

fluorenes are known for their high photoluminescence ef

chemical transformation. We hope to test the structure and properties of resultant system.

In addition, the nature of the side chains at the 9th position of fluorene will be investigated

to see if its length affects the formation of hexafluorenyl benzene.

50

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63

Chapter Two

Synthesis and Characterization of Chromophore Side Chains

during investigations

cheape er. Its

m (2.4 eV) are in the yellow-green

synthesis of PPV directly from a monomer produces an insoluble material, which cannot

yields By

to four categories:

metath zation.

.1.1 Main synthesis routes of PPV compounds

.1.1.1 Sulfonium precursor route

The precursor approach relies on the pre of a soluble precursor polymer that

can be cast into thin films and then be transformed into the final conjugated polymer

films through solid state thermo- or photo-conversion. The sulfonium precursor

route(SPR) to PPV was introduced by Wessling and Zimmerman (Figure 2.1).3,4 It was

PPV Derivatives

2.1 Introduction

Electroluminescence in conjugated polymers was first discovered

into the electrical properties of poly(1,4-phenylene vinylene) (PPV),1 the simplest and

st poly(arylene vinylene). PPV is a bright yellow, fluorescent polym

emission maxima at 551 nm (2.25 eV) and 520 n

region of the visible spectrum. The polymer is insoluble, intractable, and infusible. Any

be easily processed. Solution processing by spincoating is particularly desirable as it

high quality transparent thin films for the production of polymer EL devices.2

now, the various synthetic routes to PPVs can be roughly divided in

precursor approach, side chain derivatization, polycondensation and ring-opening

esis polymeri

2

2

paration

64

then subsequently modified and op ps.5-7 As shown in Figure 2.1, it

involved the polym

presence of a base in water or methanol to give the corresponding sulfonium precursor

polymer. The principle has been of PPV-related copolymers.

timized by other grou

erization of p-xylene bis(tetrahydrothiophene chloride) in the

applied to a whole range

CH2ClClH2CS

SCl

Clterahydrothiophene

MeOH, 650C

1. NaOH, MeOH/H O2

2. neutralization(HCl)

3. dialysis(water)

1 2

S

SCl

OMe

n

Cl

n

n

MeOH, 500C

2200C, HCl(g)/Ar, 22h

180-3000C, vaccum, 12h3

4 5

Fig. 2.1 The sulfonium precursor route(SPR)

2.1.1.2 Side chain derivatization

The side chain approach involves the polymerization of a highly substituted monomer

to a soluble conjugated polymer that can be cast into thin films directly without

conversion. The polymerization of bis(halo methyl)benzene in the presence of a large

excess of potassium tert-butoxide to PPVs is referred to as Gilch route (Figure 2.2).8 It

65

proceeds through base-promoted 1,6-elimination of 1,4-bis(halomethyl)benzene

derivatives.9-12 This shortens the preparation of the conjugated polymer by two steps and

can increase the yields. The Gilch procedure is very simple and can normally result in

polymers with high molecular weights, narrow polydispersity indices and high structural

regularity. The Gilch route has been widely used for the preparation of soluble PPV

derivatives in order to avoid the conversion step and the many problems associated with

SPR.

CH2XXH2C

R

excess baseCH CH

R nX=Cl or Br

6 7

Fig. 2.2 The Gilch route

2.1.1.3 Polycondensation methods

Polycondensation methods can be differentiated into two types13: where the carbon

skeleton of PPV is generated in an olefinic reaction with formation of olefinic bond o

d aryl-olifine-

The most common

olycondensation method for the preparation of PPV is the Wittig method. This method

weight infusible yellowish fluorescence powder. An

r

where the PPV backbone is synthesized via a transition metal-catalyze

coupling with formation of the aryl-vinyl single bond.

p

tends to produce a low molecular

advantage of the Wittig step is that the structures of the resulting polymers are well-

defined and it allows a careful control of the molecular weight. Other widely used

polycondensation methods include the Heck reaction and McMurray reaction.

66

2.1.1.4 Ring-opening metathesis polymerization (ROMP)

Ring-opening metathesis polymerization (ROMP) offers the opportunity for precise

control of polydispersity and microstructure. The siloxy-substituted cyclophane 814 or

bicyclic monomer 1115 are typical substrates for ROMP. Precursor polymers 10 and 12

are converted to PPV 5 by thermal elimination (Figure 2.3).

OSiMe2tBu

tBuMe2SiO

n

HO

n

OCO2MeOCO2Me

MeO2CO OCO2Me n

n

[Mo(=NAr)(=CHMe2Ph)-{OCMe(CF3)2}2] Bu4NF

[Mo(=NAr)(=CHMe2Ph)-{OCMe(CF3)2}2]

1050C

HCl(g), 1900C

C

8 9

2800510

11 12

Fig. 2.3 Ring-opening metathesis polymerization (ROMP) route

67

2.1.2 Application of PPV and Derivatives

Much of early works on the application of PPV focused on the wide range of

conductivity that could be achieved. Although PPV can form highly conductive materials

as coatings for EMI/RFI shielding or antistatic application upon doping, the long-term

stability of these materials may be a problem. The application potential is in

photodiodes16, photovoltaic cell17,18, optocouplers19 and electrophotography20.

Polymer light-emitting devices (PLEDs) are the most intensely investigated area for

the application of PPV derivatives. PPV provides excellent hole-transporting layers21 in

PLEDs in addition to be the active emissive layer. With precisely chemical modifications

and device engineering, PPVs give colors which cover the entire visible spectrum of

colors with good efficiencies under a bias of only a few volts. In addition, the excellent

film-forming properties of PPVs suggest that a large area display can be fabricated from

these polymer materials. In summary, PPVs have great potential as commercial display

technologies of the future.22

2.2 Molecular design

There are mainly three categories of PPV derivatives. They are alkoxy-substituted23,

phenyl-substituted24,25 and naphthalene-containing PPV derivatives26. PPV compounds

have a good planarity due to their conjugated alkene skeleton. This planarity is important

for charge separating and transfer. But aggregation was also caused by the good planarity.

This aggregation will deduce the quantum yield and solubility of polymers. In our work,

we hope to introduce huge steric hindrance chromophores as side chains into the PPV

polymers. These side chains will combine their own properties together with the PPV

68

main chain and adjust the properties of polymers. The steric hindrance caused by these

side chains can be a favorite factor to decrease the aggregation and increase the

photoluminescence efficiency of polymers. By our knowledge, in all reported PPV

polymers, there is no dichromophore substituted PPV compounds. This may be due to the

synthesis problem. In this chapter, we try to synthesize dichromophore substituted PPV

polymers and test their basic optical-electric properties.

2.3 Synthesis route

Br

Br

Br

Br

Br

Br

Br

OMe

Br MeO

i ii

1 2 3

.

BrC6H13 C6H13

(HO)2BC6H13 C6H13

iii iv

4 5 6

Br

BC6H13 C6H13

v

7

O

O.

69

+Br

Br

OMe

MeO

2

OMe

MeOC6H13

C6H13

C H6 13

C6H13

vi

7 8

BO

O

3

C6H13 C6H13

Br

BrC6H13

C6H13

C6H13

C6H13

9

vii viii

n

10

.

Polymer P1 Scheme 2.1 The synthetic routes for the Polymer P1 Reagents and conditions: (i) NBS, benzoyl peroxide, CCl4, irradiation, reflux, 4h; (ii) Na, MeOH, 12h; (iii) n-C6H13Br, 50% NaOH, Bu4NBr, 80 oC, 24h; (iv) THF, BuLi, -78 oC, 2h, then trimethylborate to r.t. 24h; (v) 1,3-propanediol, toluene, reflux, 12h; (vi) Pd (PPh3)4 (5% mole), toluene/2M Na2CO3 , 100 oC, 48h; (vii) HBr gas/CHCl3, 24h; (viii) KO(t-Bu)/THF, 24h.

70

NH

NH

i ii

11 12 13

Br

N

Br

C6H13

.

iii

NC6H13

14

BO

O

.

+Br

Br

OMe

MeO

OMe

MeO

iv

1514

NC6H13

N C6H13

3

NC6H13

BO

O

2

v

Br

Br

NC6H13

N C6H13

N

vi

16 17

N

n

.

Polymer P2

71

Scheme2.2 The synthetic routes for the Polymer P2 Reagents and conditions: (i) NBS, DMF, reflux, 12h; (ii) n-C6H13Br, KOH, MeOH,50 oC, 24h; (iii) THF, BuLi, -78oC, 2h, then 2-isopropoxy-4,4,5,5-tetramethyl 1,3,2- dioxaboralane to r.t. 24h; (iv) Pd(PPh3)4 (5% mole), toluene/2M Na2CO3 , 100 oC, 48h; (v) HBr gas, CHCl3, 24h; (vi) KO(t-Bu)/THF, 24h. .4 Results and discussion.

2.4.1 Polymer synthesis

Compared with previous literature27,28,23,29,30, Our synthesis route has two distinct

advantage. First, the normal ways attached the two or one side chain groups on the xylene

ring first and then do the bromination of two methyl groups on the xylene later.

2

Br

Br

Br

Br

Br

Br

Br

Br

OMe

MeO

R

R

OMe

MeO

R

R

Br

Br

R

R

R

R

Br

Br

R=

i. NBS/C

Cl4

ii. Na/MeOH iii. Suzuki iv. HBr

v. Suzuki coupling

vi. NBS/CCl4

coupling

C6H13 C6H13

9

Figure 2.4 Protection and deprotection of -CH2Br group on difluorenyl benzene ring

For example, in the synthesis of Polymer P1, starting from 2,5-difluorenenyl-p-

xylenen, it is hard to obtain the pure compound 9 because of the alkyl chain in the

72

fluorene group will compete the bromination process with two methyl groups of

protect the CH2Br group first and then

o chromophores were attached. It avoids bromination on the two chromophore rings’

alkyl chains. This method highly improved the yield of bromination products. Second,

our deprotecting reaction of the CH Br group in CHCl3 with HBr gas is almost

quantitative reaction and there is no need to purify the product if the precursor is pure.

This is a big progress compared the general procedure by using 48% HBr water solution

(30-40%). By this way, two different chromophores can also be attached on one xylene

ring. It makes it possible to adjust the properties of PPV in a big range by using Gilch

polymerization.

It should be mentioned that the base and reactants concentration is important in Gilch

polymerization reaction. The potassium t-butoxide is 1M in this route. The reactants

concentration should be around 0.05 M. Too dilute solution gave a very low yield of the

final product. Too concentrated solution gave a gel product.

2.4.2 Size exclusion chromatography (SEC)

er P1 and P2

)

xylene.(Figure 2.4)

Our way has a bromination reaction on the two methyl group of compound 2,5-

dibromo-p-xylene. Methoxy group was chosen to

tw

2

Table 2.1 The SEC data of polym

Polymer Mn Mw Mw/Mn(PDI

P1 42300 70300 1.66

P2 57200 67400 1.18

73

Polymer P1 is green color. Polymer P2 is yellow green color. They can dissolve in

common organic solvents such as chloroform, THF, toluene. The molecular weights of

it shows weight loss at about 426 oC. At above 500 oC, there is about

the polymer P1 and P2 were determined by means of size exclusion chromatography

(SEC) using CHCl3 as an eluent and polystyrene as the standard. Their respective number

average molecular weights (Mn), weight average molecular weights (Mw) and

polydispersity indices (PDI) are outlined in Table 2.1.

2.4.3 Thermal Analysis (TGA and DSC)

The thermal stability of the polymer P1 and P2 were evaluated by thermogravimetric

analysis (TGA). P1 shows weight loss at about 370 oC in nitrogen (Figure 2.5). At above

512 oC, there is about 50% of residue, which was produced by charring during heating.

For Polymer P2,

56% of residue. We can see polymer P2 is much stable than P1.

100

110

100 200 300 500 600 700

70

80

90

400 80040

50

P1 P2

Wei

gh

t

60

(%

)

Te (0C)mperature

ig. 2.5 The thermogravimetric analysis (TGA) of Polymer P1 and P2 in a nitrogen atmosphere F

74

The first possible volatile fragment is the alky chain attached on the carbon atom of the

fluorene (P1) and nitrogen atom of carbazole (P2). After losing the alkyl chain, the

nitrogen radical is more stable than carbon radical. That is the reason why P2 is more

stable than P1.

50 100 150 200 250

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

P1

Hea

tw

(W

/g)

0

Flo

Temperature (C)

P2

Fig. 2.6 The DSC traces of Polymer P1 and P2

Thermally induced phase transition behavior of P1 and P2 was also investigated with

differential scanning calorimetry (DSC) in a nitrogen atmosphere. The DSC curves are

shown in Figure 2.6. From these curves, we can see P1 and P2 have no obvious Tg. The

relatively high glass transition temperatures are essential for many applications, such as

emissive materials in light –emitting diodes.

2.4.4 Optical Properties (UV and PL)

The spectroscopic properties of the target polymers were measured in chloroform

roperties are summarized in Table 2.2. solution. The optical p

75

P1 exhibited the absorption maximum at 321 nm, with a small shoulder at 286 nm and

a sub-peak at 421 nm. Its PL spectrum peaked at 481 nm with a sub-peak at 381nm. P2

exhibited the absorption maximum at 301 nm with an emission at 497 nm (Figure 2.7). In

general, the presence of well-defined vibronic structures in the emission spectra indicates

at the polymer has a rigid and well-defined backbone structure.31,32 th

300 400 500 600 7000.0

0.2

0.4

0.6

0.8

1.0

1.2

0

200

400

600

800

1000

1200

Ab

so

rpti

on

(N

orm

aliz

ed

)

Wavelength (nm)

P1 Uv P1 PL P2 Uv P2 PL

PL

Inten

sity

(a.u.)

Fig. 2.7 The UV-vis absorption spectra and photoluminescence spectra of Polymer P1

Table 2.2 The optical data and fluorescence quantum yields (both in chloroform

and P2 measured from their chloroform solution at room temperature

solutions) of polymer P1 and P2

Solution λmax(nm)a Eg(eV)b PL Efficiency (%)

compound Abs. Em

P1 321(286, 421) 481(381) 3.18 76.0

P2 301 497 3.66 54.0

a. The data in the parentheses are the wavelength of shoulders and sub-peaks;

UV absorption. b. Eg stands for the band gap energy estimated from the onset wavelength of the optical

76

350 400 450 500 550 6000

50

100

150

200

250

300 CHCl

3

THF 90% THF, 10% MeOH 80% THF, 20% MeOH 20% THF, 80% MeOH 3% THF, 97% MeOH

ten

sit

(a.u

.)

PL

Iny

Wavelength (nm)

Fig. 2.8 Solvent effection on linear photoluminescence spectra of polymer P1

As shown in Figure 2.8, polymer P1 has two emission peaks. One is for the emission

of PPV backbone (around 480nm);23 the other is for the emission of PPV side

chromophore chains (around 380nm).33-35 With the different ratio of good solvent (THF

and chloroform) and poor solvent (MeOH), the area of two PL emission peaks have

obvious change. This property is very useful in biosensor detection.36,

and P2 was investigated by the Cyclic

Voltammetry (CV). The CV was performed in a solution of Bu4

temperature under the protection of argon. A

platinum electrode was used as the working electrode. A Pt wire was used as the counter

electrode and an Ag/AgNO3 electrode was used as the reference electrode. The

corresponding data are summarized in Table 2.3 and Figure 2.9.

37

2.4.5 Electrochemical Properties

The electrochemical behavior of polymer P1

NClO4 (0.10M) in

chloroform at a scan of 50 mV/s at room

77

Table 2.3 The electrochemical data of the polymers P1 and P2

a. LUMO energy level was calculated by Eg and HOMO energy level

0 1 2-1

0

2

1

4

5

3

I (m

A)

(

-2 -1 0 1 2-6

-2

2

no

r

E (V vs SCE)

P1

m.)

4

6

-4

0

8

10

I (m

A)

(

Fig. 2.9 The cyclic voltammograms of P1 and P2

no

r

E (V vs SCE)

P2

P2 has

aromatic CH2Br groups’

d deprotection reactions. The high yields of these two reactions were

uarantee of the success of whole route.

p-doping (V) Energy levels(eV) compound

Eonset Epa Epc HOMO LUMO Eg

P1 1.20 1.66 1.38 -5.60 -2.42a 3.18

P2 1.25 1.79 1.41 -5.65 -1.99 3.66

m.)

P1 and P2 have almost the same HOMO energy level (-5.60 and -5.65eV), but

a 0.4 eV higher LUMO energy level (-1.99 vs -2.42 eV). P2 is better to be used as hole

transporting materials and P1 is better to be used as emission layer materials.

2.5 Conclusion

Two novel dichromophore side chains substituted PPV compounds were successfully

synthesized. Two key steps in the whole synthesis route were

protection an

g

78

Efficient green light emission, good solubility in common organic solvents, good

thermal stability and relative high glass transition temperatures had been demonstrated in

nds. These properties made the two polymers good candidatures for efficient

green light em vices. In the mean , by o sis is poss to

attach different chromophore functio oups a chains V com s.

This will highly ase the l energy

two compou

itting de time ur synthe route, it ible

s and nal gr s side- on PP pound

incre orbita level tuning range of PPV compounds.

79

Reference

G. Chem. Abstr. 1968, 69, 87735q.

. Gilch, H. G.; Wheelwright, W. L. J. Polym. Sci., Part A: Polym. Chem. 1966, 4,

1337.

. Doi, S.; Kuwabara, M.; Noguchi, T.; Ohnishi, T. Synth. Met. 1993, 57, 4174.

0. Heeger, A. J.; Braun, D. Chem. Abstr. 1993, 118, 157401j.

1. Sarnecki, G. J.; Burn, P. L.; Kraft, A.; Friend, R. H.; Holmes, A. B. Synth. Met.

1993, 55, 914.

2. Swatos, W. J.; Gordon, B. Polym. Prepr. 1990, 31, 505.

3. Scherf, U. Top. Curr. Chem. 1999, 201, 163.

4. Miao, Y. J.; Bazan, G. C. J. Am. Chem. Soc. 1994, 116, 9379.

5. Conticello, V. P.; Gin, D. L.; Grubbs, G. H. J. Am. Chem. Soc. 1992, 114, 9708.

6. Yu, G.; Pakbaz, K.; Heeger, A. J. Appl. Phys. Lett. 1994, 64, 3422.

1. Burroughes, J. H.; Bradley, D. D. C.; Brown, A. R.; Marks, R. N.; MacKay, K.;

Friend, R. H.; Burn, P. L.; Holmes, A. B. Nature 1990, 347, 539.

2. Kraft, A.; Grimsdale, A. C.; Holmes, A. B. Angew. Chem. Int. Ed. 1998, 37, 403.

3. Wessling, R. A.; Zimmerman, R.

4. Wessling, R. A. J. Polym. Sci. Polym. Symp. 1985, 72, 55.

5. Lenz, R. W.; Han, C.-C.; Stenger-Smith, J.; Karasz, F. E. J. Polym. Sci. Polym.

Chem. 1988, 26, 3241.

6. Burn, P. L.; Bradley, D. D. C.; Friend, R. H.; Halliday, D. A.; Holmes, A. B.;

Jackson, R. W.; Kraft, A. J. Chem. Soc. Perkin Trans. 1 1992, 3225.

7. Garay, R. O.; Baier, U.; Bubeck, C.; Müllen, K. Adv. Mater. 1993, 5, 561.

8

9

1

1

1

1

1

1

1

80

17. Antoniadis, H.; Hsieh, B. R.; Abkowitz, M. A.; Jenekhe, S. A.; Stolka, M. Synth.

Met. 1994, 62, 265.

8. Karg, S.; Reiss, W.; Meier, M.; Schwoerer, M. Synth. Met. 1993, 55, 4186.

9. Yu, G.; Zhang, C.; Pakbaz, K.; Heeger, A. J. Synth. Met. 1995, 71, 2241.

0. Drefahl, G.; Hörhold, H.-H.; Opfermanm, J. GDR Patent 75233, 1970.

1. Brown, A. R.; Bradley, D. D. C.; Burroughes, J. H.; Friend, R. H.; Greeham, N.

C.; Burn, P. L.; Holmes, A. B.; pl. Phys. Lett. 1992, 61, 2793.

22. Light-Emitting Polymers: The Technology and Opportunities; Technical Insights

23.

Appl. Phys. 1993, 32,

27. H. S.; Huang, W.; Xu, Y. S.; Cao, Y. Macromolecules

28. r, I. D.; Cao,

H. Adv. Mater. 1998, 10, 1340.

32,

1

1

2

2

Kraft, A. Ap

Inc., 1996.

Braun, D.; Heeger, A. J. Appl. Phys. Lett. 1991, 58, 1982.

24. Peng, Z. H.; Pan, Y. C.; Xu, B. B.; Zhang, J. H. Macromol. Symp. 2000, 154, 245.

25. Peng, Z. H.; Zhang, J. H.; Xu, B. B. Macromolecules 1999, 32, 5162.

26. Onada, M.; Uchida, M.; Ohmori, Y.; Yoshino, K. Jpn. J.

3895.

Chen, Z. K.; Nancy, L.

2003, 36, 1009.

Becker, H.; Spreitzer, H.; Kreuder, W.; Kiuge, E.; Schenk, H.; Parke

Y. Adv. Mater. 2000, 12, 42.

29. Spreitzer, H.; Becker, H.; Kluge, E.; Kreuder, W.; Schenk, H.; Demandt, R.;

Schoo,

30. Becker, H.; Spreitzer, H.; Ibrom, K.; Kreuder, W. Macromolecules 1999,

4925.

81

31. Miyaura, N.; Yamada, K.; Suginome, H.; Suzuki, A. J. Am. Chem. Soc. 1985, 107,

972.

32. Suzuki, A. Pure Appl. Chem. 1985, 57, 1749.

33. Pei, Q. B.; Yang, Y. J. Am. Chem. Soc. 1996, 118, 7416.

2000, 12,

37. Kohler, B.; Korystov, D.; Mikhailovsky, A.; Bazan, G. C. J.

34. Bernius, M. T.; Inbasekaran, M.; OBrien, J.; Wu, W. S. Adv. Mater.

1737.

35. Ranger, M.; Leclerc, M. Macromolecules 1997, 30, 7686.

36. Liu, B.; Bazan, G. C. J. Am. Chem. Soc. 2004, 126, 1942.

Woo, H. Y.; Liu, B.;

Am. Chem. Soc. 2005, 127, 14721.

82

Chapter Three

ymers

3.1 Introduction

Conjugated organic compounds play a primary role in the development of a new

generation of optical and electronic materials. Small molecules, oligomers, and polymers

with carbon, heteroatomic, or organometallic frameworks have been widely explored as

media for electroluminescence, data storage, and nonlinear optics.1,2 The most intensely

studied conjugated molecules with carbon-rich frameworks focus on extended linearly-

conjugated π-systems.

During the 20th century, the interest of organic chemists was captured by the definition

of aromaticity based on theoretical principles and on the power of those principles to

guide the synthesis of novel nonbenzenoid aromatic compounds.

Fulvalenes are molecules with two unsaturated ring systems showing cross conjugation

through the interring double bond and capable of generating two separate aromatic

moieties.4-10 Tetrabenzo[5.5]fulvalene, a basic bistricyclic aromatic system, was widely

used to study its aromaticity by energetic, structural (geometric), and magnetic

escriptors of aromaticity.11-15 By our knowledge, no report has been made on

trabenzo[5.5]fulvalene’s usage in materials. Our target is to synthesize

trabenzo[5.5]fulvalene based polymer. We hope to explore how the

trabenzo[5.5]fulvalene make an effect on polymer properties and find the potential

pplication for polymers .

Synthesis and characterization of tetrabenzo[5.5]fulvalene

based pol

3

d

te

te

te

a

83

O

BrH

iii

iii iv

Scheme 3.1 General synthesis routes of tetrabenzo[5.5]fulvalene. i) CrO3/CH3COOH; ii) TiCl4/Zn, THF; iii) NBS/benzene; iv) KOH/DMSO. There are two general ways to obtain the tetrabenzo[5.5]fulvalene (Scheme3.1). But by

these two ways only the symmetric structure can be obtained. For the nonsymmetric

structure tetrabenzo[5.5]fulvalene, we can only choose the route in Scheme 3.2.11


Br Br Br Br

O

i.

1 2

Br Br

O

Br Br+

ii

.

3 2 4

Scheme 3.2 Synthesis routes for monomer 4. Reagents and conditions: (i)CrO3/ CH3COOH; (ii) a) 1 equiv. BuLi, Si(Me)3 Cl/ THF; b) 1 equiv. BuLi.

84

Br BrBrBr B(OH)2(HO)2B

iii

1 6

iv

5

vBO

O BO

O

7

.

NH N

H

Br Br

N

Br Brvi vii

.

8 9 10

N

viii BO

OBO

O

11

Scheme 3.3 Synthesis routes for monomer 7 and 11. Reagents and conditions: (iii) n-C6H13Br, 50% NaOH, Bu4NBr, 80 C, 24h; (iv) THF, BuLi, -78 C, 2h, then trimethylborate to r.t.; (v) 1,3-propanediol, toluene, reflux, 12h; (vi) NBS, DMF, reflux, 12h; (vii) n-C6H13Br, KOH, MeOH, 50 C, 24h; viii) THF, BuLi, -78oC, 2h, then 2-isopropoxy-4,4,5,5-tetramethyl 1,3,2- dioxaboralane to r.t.

.

o o

o

85

Br Br

+ ix

n

BO

OBO

O

7 4 12

Polymer P1

N

B O

OBOO

11

Br Br

N

n

+ix

4 13

Polymer P2

Scheme 3.4 Synthesis routes for polymer P1 and P2. Reagents and conditions: (ix) Pd(PPh3)4 (5% mole), toluene/2M Na2CO3 , 100 oC, 48h; In Scheme 3.2, 9-trimethylsilylfluorene was first formed by using trimethylsilyl

chloride and fluorene in the condition of 1 equivalent of n-Butyllithium. Then another 1

equivalent of n-Butyllithium was used to remove the remaining proton atom from 9

position of fluorene. This negative ion reacted with 2, 7- dibromofluorenone to obtain the

final product 9-(9H-Fluoren-9-ylidene)-2, 7-dichloro-9H-fluorene.

86

3.3 Results and discussion.

3.3.1 Size exclusion chromatography (SEC)

Table 3.1 The SEC data of polymer P1 and P2

Polymer Mn Mw Mw/Mn

P1 7200 11300 1.58

P2 5500 7000 1.28

Polymer P1 and polymer P2 are brown yellow color. They can dissolve in common

organic solvents, such as chloroform, THF, toluene. The molecular weights of the

polymer P1 and P2 were determined by means of size exclusion chromatography (SEC)

using CHCl3 as an eluent and polystyrene as the standard. Their respective number

average molecular weights (Mn), weight average molecular weights (Mw) and

polydispersity indices (PDI) are outlined in Table 3.1. The molecular weight of P1 and

P2 are not high because the planar structure of tetrabenzo[5.5]fulvalene units make the

whole molecule to be good packing and reduce the solubility in the reaction solvent.


The thermal stability of the polymers in nitrogen was evaluated by thermogravimetric

analysis (TGA). P1 shows weight loss at about 327 oC in nitrogen. Above 570 oC, there is

about 60% of residue, which was produced by charring during heating. P2 shows weight

loss at about 335 oC in nitrogen (Figure 3.1). Above 470 oC, there is about 67% of residue.

All these indicate a good thermal stability.

87

88

Fig. 3.1 The thermogravimetric analysis (TGA) of P1 & P2 in a nitrogen atmosphere

Thermally induced phase transition behavior of P1 and P2 was also investigated with

differential scanning calorimetry (DSC) in a nitrogen atmosphere (Figure 3.2).

0 100 200 300 400 500 600 700 80050

60

70

80

90

100

Wei

gh

t(%

)

Temperature (0C)

P1 P2

50 100 150 200-1.8

-1.6

-1.2

-1.4

-0.8

-1.0

t F

lo(W

/g)

Hea

w

Temperature (0C)

P1 P2

Fig. 3.2 The DSC traces of P1 and P2

The DSC curves are shown in Figure 3.2. From these curves, we can see P1 has a Tg at

6 oC. This shows the introducing of carbazole units into the

gmental movement of the polymer chain.

y chain attached on

the carbon atom of the fluore 1) and nitrogen ato carbazole (P2

the alkyl chain, the nitrogen radical is more stable than carbon radical. That is the reason

why P2 more stable than he relatively high transition temp es are

ential for many applications, such as emissive materials in light –emitting diodes.16

rigid

nd well-defined backbone structure.

115 oC and P2 has a Tg at 17

polymer mains has a profound effect on the se

In the heating process, the first possible volatile fragment is the alk

ne (P m of ). After losing

is P1. T glass eratur

ess


The spectroscopic properties of the target polymers were measured in chloroform

solution. The optical properties are summarized in Figure 3.3 and Table 3.2.

P1 exhibited the absorption maximum at 369 nm, with a sub-peak at 466 nm. Its PL

spectrum peaked at 411 nm. P2 exhibited the absorption maximum at 312 nm, with a

sub-peak at 467 nm. Its PL spectrum peaked at 487 nm. In general, the presence of well-

defined vibronic structures in the emission spectra indicates that the polymer has a

a

89

ig. 3.3 The UV-vis absorption spectra and photoluminescence spectrum of Polymer P1 and P2 measured from their chloroform solution at room temperature

Table 3.2 The optical data and fluorescence quantum yields (both in chloroform solutions) of polymer P1 and P2


300 400 500 600 7000.0

0.2

0.4

0.6

0.8

1.0

1.2

0

200

400

600

800

1000

1200

Ab

sorp

tio

n (

No

rma

lized

)

Wavelength (nm)

P1 UV P2 UV P1 PL P2 PL

PL

Inten

sity

(a.u.)

F

compound Abs. Em

P1 369 (466) 411 3.00 20%

P2 312 (467) 487 3.26 12%

a. The data in the parentheses are the wavelength of shoulders and sub-peaks; b. Eg stands for the band gap energy estimated from the onset wavelength of the optical UV absorption. Polymer P1 and P2 have relatively lower photoluminescence efficiency (20% and

18%). Their tetrabenzo[5.5]fulvalene units in polymer caused a good packing which can

quench the emission.

90


The electrochemical behavior of polymer P1 and P2 were investigated by the Cyclic

Voltammetry (CV). The CV was performed in a solution of Bu4NClO4 (0.10M) in

chloroform at a scan of 50 mV/s at room temperature under the protection of argon. A



corresponding data are summarized in Figure 3.3 and Table 3.3.

-1 0 1 2-1

0

1

2

3

4

5

6

I (m

A)

(n

0

2

o

E (V vs SCE)

P1

rm.)

0 1 2-2

4

6

I (m

A)

(no

rm.)

E (V vs SCE)

P2

ers P1 and P2

p-doping (V) Energy levels(eV)

Fig3.4 The cyclic voltammograms of P1 and P2

Table 3.3 The electrochemical data of the polym

compound

Eonset Epa Epc HOMO LUMOa Eg

P1 1.10 1.67 1.45 -5.50 -3.16 2.34

P2 0.91 2.00 1.44 -5.31 -3.02 2.29


91

3.3.5 Comparison of our novel polymers with some analogues

Table 3.4 comparison of polymer P1, P2 with analogues

Polymers Absorption

(λm)

Emission

(λm)

Band gap(eV)

/PL efficiency (%)

C6H13 nC6H13

Fl-Fl-C617

379 415 2.86/82.22

C6H13 nC6H13NC8H17 17Fl-C6-CB-C8

348 398 3.06/26.3

C6H13 nC6H13

18Fl-C6-SpirobiFl

.6 425(EL) N.A. N.A./34

C6H13C6H13

n P1

369 411 3.00/20

N

n

C6H13

P2

312 487 3.26/12

The UV absorption, PL emission, band gap and PL efficiency of our novel polymer P1,

ads to the essential lowering of the energy of the fluorescent term

P2 and some analogues are shown in Table 3.4. It is interesting that polymer P2 has the

biggest Stokes shift. This shows that Polymer P2 undergoes noticeable flattening in their

excited state, which le

92

and, in turn, enlargement of the Stokes shift of the fluorescence.19 Polymer P1 has almost

ers were successfully

synthesized. The key step in the whole synthesis route was the synthesis reaction of

dibromo-tetrabenzo[5.5]fulvalene.

Good solubility in common organic solvents, good thermal stability and relative high

glass transition temperatures had been demonstrated in these two compounds. Although

the quantum yield of the two polymers were low due to the good packing of the

tetrabenzo[5.5]fulvalene units. This kind of compounds can still have the potential to be

used in solar cell and organic field effect transistor. In the meantime, this is the first time

to introduce tetrabenzo[5.5]fulvalene units into polymer compounds. We hope to explore

more properties of this kind of polymers in the future research work.

the same absorption, emission and band gap with polyfluorene (F1-F1-C6). But its PL

efficiency is much lower than polyfluorene(F1-F1-C6). This quantum yield quenching

was caused by the good packing of tetrabenzo[5.5]fulvalene units.

3.4 Conclusion

Two novel tetrabenzo[5.5]fulvalene units containing polym

93

Reference

1. Meier, H. Angew. Chem., Int. Ed. 2005, 44, 2482.

2. Martin, R., E.; Diederich, F. Angew. Chem. Int. Ed. 1999, 38, 1350.

3. Gholami, M.; Tykwinski, R. R. Chem. ReV. 2006, 106, 4997.

Kleinpeter, E.; Holzberger, A.; Wacker, P. J. Org. Chem. 2008, 73, 56.

5. Mills, N. S.; Malandra, J. L.; Hensen, A.; Lowery, J. A. Polycyclic Aromatic

, 239.

6. Bagrat A, S.; Anja, F.; Erich, K. J. Phys. Chem. A 2008, 112, 10859.

7. Shainyan, B. A.; Fettke, A.; Kleinpeter, E. 2008,

8. Piekarski, A. M.; Mills, N. S.; Yousef, A. J. Am. Chem. Soc.

9. Dahl, B. J.; Mills, N. S. Org. Lett. 2008, 10, 5605.

10. Pogodin, S.; Agranat, I. J. Org. Chem. 2007, 096.

11. Mills, N. S.; Burns, E. E.; Hodges, J.; Gibbs, J.; Esparza, E.; Malandra, J. L.;

Koch, J. J. Org. Chem. 1998, 63, 3017.

12. ls, N . J. Am. Chem. Soc. 2008, 130, 10179.

13. Mills, N. S.; Benish, M. Journal of Organic Chemistry 2006, 71, 2207.

14. Levy, A.; Rakowitz, A.; Mills, N. S. J. Org. Chem. 2003, 68, 3990.

15. Mills, N. S. J. Am. Chem. Soc. 1999, 121, 11690.

16. Tokito, S.; Tanaka, H.; Noda, K.; Okada, A.; Taga, Y. Appl. Phys. Lett. 1997, 70,

1929.

17. Liu, B.; Yu, W. L.; Lai, Y. H.; Huang, W. Chem. Mater. 2001, 13, 1984.

4.

Compounds 1998, 12

J. Am. Chem. Soc. 112, 10895.

2008, 130, 14883.

72, 10

Dahl, B. J.; Mil . S

94

18. Yang, C. M.; Liao, H. H.; Horng, S. F.; Meng, H. F.; Tseng, S. R.; Hsu, C. S.

Synth. Met. 2008, 158, 25.

19. Doroshenko., A. O.; Kirichenko., A. V.; Mitina, V. G.; Ponomaryov, O. A.

Journal of Photochemistry and Photobiology A: Chemistry 1996, 94, 15.

95

Chapter Four

Synthesis and Characterization of Chromophore Substituted

[2.2]Paracyclophane Derivatives

.1 Introduction

Cyclophane, a name first proposed by D. J. Cram,1 was originally defined as a

olecule that possesses layered aromatic moieties or a molecule that has bridges across

e plane of an aromatic moiety. Cyclophane, in which two benzene rings are close to

ach other and cofacial, is attractive in its structure, reactivity and physical properties.2,3

Although drawn flat for clarity, ring strain distorts substantially the aromatic rings. The

distance between bridgehead carbons on opposing rings is ~ 2.78 Å, while the distance

arbon bonds is ~ 3.09 Å.3 In

ent ne-containing

yme materials.

4

m

th

e

between rings measured from the nonbridging carbon-c

rec years, the cyclophane compounds research focused on cyclopha

pol rs, cyclophane chiral ligands and cyclophane nonlinear optical

Side view Top View(pCp)

Fig. 4.1 Paracyclophane

4.1.1 Cyclophane-containing Polymers

Cyclophanes have optically, electrically, and topologically intriguing features.3-5 The

addition of cyclophane compounds in polymer main chains as well as polymer side

chains as pendent groups can lead to potential applications of the resulting polymers.6

96

4.1.1.1 [2, 2] Paracyclophane-containing conjugated polymers

mers with extended conjugation contain Poly ing [2.2]paracyclophane were reported in

othienyl-substituted

groups.7-10

the 2000s. The electrochemical polymerization of olig

paracyclophanes was performed independently by two research

SS

SS

SS

SS

Electrolicpolymerizatiom

n

units

[2.2]paracyclophane unit were prepared by Prof. Y. Chujo’s group11-20 through

21,22 23-25

and Su o afford

ell-defined and well characterized [2.2]paracyclophane-containing conjugated polymers

ue to copolymerization with aromatic compounds possessing long alkyl chains.

Fig. 4.2 Conjugated polymers including oligothiophene and [2.2]paracyclophane

As shown in Figure 4.3, conjugated polymers containing a repeating

palladium-catalyzed cross-coupling reactions, i.e., Sonogashira , Mizoroki–Heck

zuki–Miyaura26,27 coupling reactions. These reactions enabled them t

w

d

OC12H25

C12H25O

nOC12H25

C12H25O

Fe

CC12H25

C12H25

n

Fig. 4.3 Main-chain-type [2.2]paracyclophane-containing conjugated polymers.

97

4.1.1.2 Rigid-rod conjugated polymers containing pendent aromatic rings

A linear conjugated polymer possessing aromatic rings as a pendent group was

esigned and synthesized by our group(type B).28-31 For example, a series of

ithia[3.3]paracyclophane-fluorene copolymers were synthesized by employing the

uzuki–Miyaura coupling reaction. The external aromatic group affects the electronic

nd optical properties of the polymer backbone through the transannular π–π interaction.

he PL efficiency of some polymers was enhanced or significantly decreased by the

endent aromatic rings. Intramolecular electron transfer from the polymer main chain to

e external aromatic rings occurred via the through-space interaction.

d

d

S

a

T

p

th

- system

- system

ty

pe A

.

S

- systemS

S

S

S

S - system

type B

.

98

SC6H13

C6H13

SRR n

SC6H13

C6H13

S n

R=H,

=75%

R=OMe,

R=CN, =0%PL

PL

PL

=36%

PL =50%

PL =5%

PL =78%

In Figure 4.5, the polymer contains bipyridinophane as the pendent unit in the

phenylene-fluorenylene polymer backbone31. It exhibited red-shifts of the absorption and

emission spectra in comparison with phenylene-fluorenylene without the bipyridinophane

nit, and they occurred due to the intramolecular edge-tilted T intramolecular aromatic

Fig. 4.4 Dithia[3.3]paracyclophane-fluorene copolymers

u

C–H/π interaction. The ion-sensing properties were studied. The fluorescence of the

polymer was efficiently quenched due to the presence of transition-metal cations such as

Cu2+, Co2+, Ni2+, Zn2+, Mn2+, and Ag+.

99

hv X

S

C6H13C6H13

SN

N

HH

n

S

C6H13C6H13

SN

N

HH

n

Mn+

Mn+

Mn+= Cu2+, Co2+, Ni2+Zn2+, Mn2+, Ag+

.1.2 Cyclophane chiral ligands

Chiral [2.2]paracyclophane derivatives have found considerable use in stereoselective

and their

Fig. 4.5 The detection of Mn+ by dithia[3.3]paracyclophane-fluorene polymers

4

synthesis. They undergo racemisation only at relatively high temperatures,

cyclophane backbone is chemically stable towards light, oxidation, acids and bases.32-35

The majority of [2.2]paracyclophane ligands or reagents are based on one of five

different substitution patterns(Figure 4.6).36

R1

mono ortho

R1

R2R2R1

pseudo-ortho pseudo-geminal bridge substituted

R1

R2 R1

R2

Fig. 4.6 [2.2]Paracyclophane substitution patterns and ligands.

Unlike other common planar chiral scaffolds, such as metallocenes or metal–arene

complexes that require two (or more) substituents on one ring to become chiral,

[2.2]paracyclophane only requires one substituent to break the symmetry of the molecule.

100

Prior to the advent of PHANEPHOS 4,12-bis(diphenylphosphino)

[2.2]paracyclophane , a pseudo-ortho disubstituted derivative, as chiral ligand in 1997,37-

39 few results on the use of [2.2]paracyclophane in stereoselective synthesis were reported.

The results obtained with PHANEPHOS and related compounds suggest that cyclophanes

bearing donor atoms on both rings may be viewed as a highly selective class of ligand

omparable with some of the best ligand classes available for asymmetric catalysis such

s the binaphthyl backbone of BINAP and the 1, 2-disubstituted ferrocene backbone of

SIPHOS. It is thus of considerable interest to develop new synthetic approaches to

chiral cyclophanes bearing both identical and non-identical substituents on their two rings.

It is the great success of PHANEPHOS in enantioselective hydrogenations that has

fuelled research into the utility of [2.2]paracyclophane as a scaffold for the preparation of

chiral ligands.

Planar chiral monosubstituted [2.2]paracyclophane derivatives have been employed in

asymmetric diisopropylzinc additions to aldehydes, asymmetric cyclopropanation

reactions and asymmetric epoxidation reactions.40-44 These pioneering studies as shown

in Figure 4.16 have produced moderate to excellent enantioselectivities and yields.45 But

most of the monosubstituted [2.2]paracyclophane derivatives majority show moderate to

low enantioselectivities, presumably due to excessive conformational freedom.46

4.1.3 Cyclophane nonlinear optical materials.

In recent years, almost all of the research work on cyclophane containing nonlinear

optical materials was done by Professor Bazan’s group,47 they set out to synthesize

precisely determined molecular structures that bring together two chromophores into

,

c

a

JO

101

close proximity and would make it possible to probe the effect of orientation, contact site,

and the length of electronic delocalization on the optical properties. The goal was to

better understand the problems of “through-space” delocalization. Their strategy was to

take advantage of the paracyclophane framework48-50 as the site of interchromophore

contact51,52 since it enforces cofacial overlap of two aromatic rings, minimizes

tramolecular motion, and has proven useful for the study of π-π electron delocalization

and ring strain in several organic compounds.

Calculations predicted that more facile charge transport could be achieved by a

monolayer of strongly interacting conjugated molecules due to the formation of a pseudo

two-dimensional band structure in the molecular layer.53 Building an interdigitated

molecular bilayer using [2.2]paracyclophane allows one to obtain the necessary strong

electronic coupling while at the same time enforcing a cofacial relationship between the

ctive units.

[2.2]paracyclophanes

in

a

4.1.3.1 Synthesis and characterization of chromophores substituted

CMe3Me3C

CMe3Me3C

Me3C

Me3C CMe3

CMe3

Fig. 4.7 Tetra- substituted Cyclophanes.

102

Two molecules in Figure 4.7 display electronic delocalization throughout their

structures makes them interesting within the context of three-dimensional conjugation.

Such molecular systems are described by symmetry elements not contained within the

structures of linear or two-dimensional analogues. The [2.2]paracyclophane framework

unit that is

me

n’s studies, a successful approach had been put forth that involved a

provides a suitable backbone in the form of a polarizable transmitting

amenable for subsequent functionalization. For this effort, they collaborated with the

research groups of Professors Joe Zyss and Shaul Mukamel to provide a combined

synthesis, spectroscopy, and theory effort to understand the potential and limitations of

higher sym try nonlinear optical chromophores.54

For constructing a rationale for the structure/optical properties relationships in the class

of compounds in these molecules, the collective electronic oscillator (CEO) approach was

used. CEO approach55-57 demonstrated previous success at describing the optical response

of chromophore aggregates. This technique computes molecular vertical excitation

4.1.3.2 Two photon absorption (TPA) performance of paracyclophanes

Organic molecules that exhibit large two-photon absorption (TPA) cross sections (δ)

are relevant to emerging technologies such as three-dimensional optical data storage,58,59

photodynamic therapy,60,61 two-photon optical power limiting,62-66 and two photon three-

dimensional microfabrication.67-74 Coordinated synthetic, spectroscopic, and theoretical

studies have yielded insight into how to better design molecules with large δ values. In

Professor Baza

framework for mobile π-electrons with electron donor/acceptor groups on the terminal

sites with or without donor/acceptor groups in the middle of the conjugated framework.75

The collective electronic oscillator (CEO) method indicates extensive delocalization

103

throughout the entire molecule. Such quadrupolar systems provide the potential for

symmetric charge displacement upon excitation and enhanced TPA. (Figure 4.8)

NHex2Hex2N

NHex2Hex2N

Hex2N NHex2

NHex2Hex2N

Figure 4.8 Quadrupolar cyclophane systems

4.1.3.3 Charge transport through paracyclophanes

The research work on charge transport of covalently linked chromophores across a

single molecule or a single molecular layer was reported.76 Experiments have

demonstrated that molecules addressed in parallel act as independent conductance

channels,77-79 namely, an ensemble of mole

cules behaves the sum of the individual

molecular conductances.

SAc

AcS

SAc

AcS

are embedded within the complex mixture of

Fig. 4.9 Cyclophane molecular structures used for charge transport

In conclusion, the work on [2.2]paracyclophane structures provides a useful tool to

probe optical and electronic properties that

sites characteristic of organic materials.

104

4.2 Molecular Design

Direct bromination of [2, 2] parcyclophane47 was used in almost all of the works to

obtain the desired cyclophane bromides from which functional groups can be attached on.

There are three shortages of this method. First, Because the eight carbons on the two

aromatic benzene rings of the[2, 2] paracyclophane had same reactivity, bromination

products of [2, 2] paracyclophane were very complicated, which caused burdensome

works on separation and very low52 (normally < 20%) yields of desired bromides. Second,

only the same functional groups can be attached on the cyclophanes because of the same

activity of bromine atoms on the cyclophanes rings. This heavily limited the properties

tunability of cyclophanes derivatives. Third, the yields of extension reactions of

cyclophanes were not high due to the forming of different substitution byproducts which

also caused the separation problem.

80

52

PPh

PPh

2

2

SS

n

C8H17

C8H17

R

R

R

R

R

R

R

R

Br

Br

Br

Br

Br

Br

Br

Br

Fig. 4.10 Normal ways to construct cyclophane derivatives structures

105

We hope to construct cyclophane core by using coupling reaction. By this method, we

can attach the wanted functional groups on the two aromatic benzene rings first. Then we

can use two same or different substituted benzene rings to form the cyclophane core. This

gives us wider choice to introduce different functional groups on the cyclophane cores.

For example, some electro-withdrawing groups on one ring and some electron-donating

group on another ring, these two rings coupling will form a donator-π delocalization-

acceptor molecule and makes cyclophane cores more easily to reach our target molecule.

The highly increased tunability will strongly stimulates the application of cyclophane

derivatives. In our whole synthesis route, we estimate that the key step is the coupling

reaction and hope the other steps reactions yields should be satisfactory. The

retrosynthetic analysis is shown in Figure 4.11

R1

R1

R2

R2

R1

R1

OMe

MeO

R2

R2

Br

Br

OMe

MeO

Br

Br

Br

Br

Br

Br

Br

Br

R2

R2

SH

HS

Br

R1

R1

Br

OMe

R2

R2

MeO

Fig. 4.11 Retrosynthetic analysis of target tetrasubstituted [2.2]paracyclophane

106

4.3 Synthesis and characterization

4.3.1 Synthesis of (4,7,12,15)-Tetra(9,9-di-n-hexyl-fluoren-2-yl) [2,2]paracyclophane

(2F2F)

Br

Br

Br

Br

Br

Br

MeO

Br

Br

i ii.

OMe

1 2 3

BrC6H13 C6H13

(HO)2BC6H13 C6H13

iii iv

4 5 6

Br

v OB

C H6 13 C H6 13

7

O.

+Br

Br

OMe

MeO MeO

2

OMe

C H6 13

C6H13

C6H13

C6H13

vi

7 8

BC6H13 C6H13

O

O

3

107

Br

BrC6H13

C6H13

C6H13

C6H13

SH

HSC6H13

C6H13

C6H13

C6H13

9 10

vii viii

C6H13

C6H13

C6H13

S

C6H139 + 10

SC6H13

C6H13

C6H13

11 (DiS2F2F)

ix

C6H13

C6H13

C6H13

C6H13

C6H13

C6H13

C H6 13

C H6 13C6H13

x

(2F2F)12

108

Scheme 4.1 Synthetic reagents and conditions: (i) NBS, benzoyl peroxide, CCl4, irradiation, reflux, 4h; (ii) Na, MeOH, 12h; (iii) n-C6H13Br, 50% NaOH, Bu4NBr, 80 oC, 24h; (iv) THF, BuLi, -78 oC, 2h, then trimethylborate to r.t.; (v) 1,3-propanediol, toluene, reflux, 12h; (vi) Pd(PPh3)4 (5% mole), toluene/2M Na2CO3 , 100 oC, 48h; (vii) HBr /CHCl3, 24h; (viii) Thiourea, MeOH , reflux, 2h, then NaOH reflux, 2h; (ix) KOH, Ethanol/Hexane, N2, 24h; (x) P(OMe)3, Uv irradiation, 24h.

4.3.2 Synthesis of (4,7,12,15)-Tetra(N-n-hexylcarbazole -3 -yl) [2,2]paracyclophane

(2C2C) and (4,7)-Bis(9,9-di-n-hexyl-fluorene-2-yl)-(12,15)-bis(N-n-

hexylcarbazole -3 -yl) [2,2]paracyclophane (2F2C)

NH

NH

i iiBr Br

NC6H13

13 14 15

BO

Oiii

NC6H13

16

109

+Br

Br

OMe

MeO

OMe

MeO

iv

1716

NC6H13

N C6H13

7

NC6H13

BO

O

+Br

Br

OMe

MeO

OMe

MeO

iv

1716

NC6H13

N C6H13

3

NC6H13

BO

O

2

v

Br

Br

NC6H13

N C6H13

SH

HS

NC6H13

N C6H13vi

18 19

110

S

S

18 + 19

20 (DiS2C2C)

viiN C6H13

NC6H13

NC6H13

NC6H13

21 (2C2C)

N C6H13

NC6H13

NC6H13

NC6H13

viii

Br

Br

NC6H13

N C H

HSC6H13

6 13C6H13

18

+SH

C H6 13

C H

vii

6 13

10

111

S

S

22 (DiS2F2C)

NC6H13

NC6H13

C6H13

C6H13

C6H13

C6H13

viii

23 (2F2C)

NC6H13

NC6H13

C6H13

C6H13

C6H13

C6H13

Scheme 4.2 Synthetic reagents and conditions: (i) NBS, DMF, reflux, 12h; (ii) n- C6H13Br, KOH, MeOH, 50 oC, 24h; (iii) THF, BuLi, -78 oC, 2h, then 2- isopropoxy-4,4,5,5-tetramethyl 1,3,2- dioxaboralane to r.t.; (iv) Pd(PPh3)4

(5% mole), toluene/2M Na2CO3 ,100 oC, 48h; (v) HBr gas, CHCl3, 24h; (vi) Thiourea, MeOH, reflux, 2h, and then NaOH reflux, 2h; (vii) KOH, Ethanol/Hexane, N2, 24h; (viii) P(OMe)3, UV irradiation, 24h.

4.3.3 Synthesis of (4,7)-Bis(9,9-di-n-hexyl-fluoren-2-yl)-(12,15)-bis(thiophene-2-yl)

[2,2]paracyclophane (2F2T) and (4,7)-Bis(N-n-hexylcarbazole-3-yl)-(12,15)-

bis(thiophene-2-yl) [2,2]paracyclophane (2C2T)

S S B(OH)2i

2524

112

Br

Br

OMe

MeO

7

+

OMe

MeOS

S

Br

S

S

Br

ii iii

26 27

S B(OH)2

25

SH

HSC6H13

C6H13

C6H13C6H13

10

+

Br

S

S

Br

iv

27

.

28 (DiS2F2T)

C6H13

C6H13

C6H13

C6H13

S

S v

29 (2F2T)

C6H13

C6H13

C6H13

C6H13

S

S

S

S .

113

SH

HS

NC6H13

N C6H13

19

+

Br

S

S

Br

27

iv.

30 (DiS2C2T)

S

S

NC6H13

NC6H13

S

S

S

S

NC6H13

NC6H13

31 (2C2T)

v .

Scheme 4.3 Synthetic reagents and conditions: (i) THF, BuLi, -78 oC, 2h, then trimethylborate to r.t.; (ii) (PPh3)4Pd (5% mole), toluene/2M Na2CO3 , 100 oC, 48h; (iii) HBr gas, CHCl3, 24h; (iv) KOH, Ethanol/Hexane, N2, 24h; (v) KOH, Ethanol/Hexane, N2, 24h; (v) P(OMe)3, Uv irradiation, 24h. 4.4 Results and Discussion

4.4.1 Synthesis methodology

Suzuki coupling reaction was chosen to attach the functional R groups on the benzene

rings. There were two key steps in the whole synthesis route.

First, methoxy groups were chosen to protect –CH2Br group in the Suzuki coupling

reaction. By this method, we can freely att h different functional groups on the 2, 5-ac

114

position of the benzene with no forming of complicated methyl group bromination

byproducts. (Figure 4.12)

Br

Br

Br

Br

Br

Br

OMe

Br

Br

MeO

OMe

R1

R1

MeO

Br

R1ii. Na/MeOH iii. Suzuki iv. HBr

R1

Br

R1

R1

R1

R1

Br

Br

i.

l4

v. Suzuki coupling

vi. NBS/CCl4

NBS/CC coupling

Route 1

Complicated bromination byproductscaused by the alkyl groups on R1

Route 2

Fig. 4.12 Protection and deprotection of -CH2Br group on the benzene ring

As shown in Figure 4.26, Route 2 can not be processed because of the complicated

bromination byproducts caused by the alkyl groups on R1. In Route 1, sodium methoxide

was chosen to protect –CH2Br group and HBr gas was chosen as the deprotecting reagent.

Although there were two more steps than Route 2, the yield of Route 1 was still

satisfactory because step ii and step iv were almost quantitative reactions and no silica gel

column purification were needed if the precursors in these two reactions were pure. It

should be noted that using HBr gas in chloroform system as deprotecting reagent was

much better than traditional HBr water solution. The latter had only about 30% yield and

any byproducts. The separation also caused much efforts because the –CH2Br group

as active in silica gel column. In summary, although two more steps were used to

protect and deprotect the benzyl bromide group, the whole yield of route 1 was still

determined by the Suzuki coupling reaction of step iii.

m

w

115

Second, after the high dilution coupling reaction, How to remove two sulphur atoms

from [3.3] dithiaparacyclophane to form [2.2] paracyclophane was a big challenge in this

synthesis route. By our knowledge, there were four normal ways to obtain the final

products from dithioether compounds as shown in Figure 4.13.

SO2 SO2

350-4000C

High vaccum

S S

H3CS

SCH3

CH2Cl2/CBr2CF2

KOH/Al2O3, 00C

LDACH

3 IRaney Nickle

H2/Pd(CH

3 O)2 CH +BF

4 -NaH, THF

H 2O 2

H 2

Pd/

C

Route 1

Route 2

Route 3

Route 4

P(OM

e)3 /Uv

reactor

Fig. 4.13 Synthesis of [2.2]paracyclophanes from [3.3]dithiaparacyclophanes precursors

The pyrolytic method in Route 1 needs a high temperature and very high vacuum

degree reaction instrument which can not be equipped by most of the labs. We tried

utes 2, 3 and 4. Although Ramberg Backlund reaction in Route 2 was very simple, but

omplete the whole reaction and the overall yield is very low (0.3%).

ro

no final products was obtained maybe due to the huge bulky substitution groups’

affection on the form of intermediate. The Stevens rearrangement method in Route 3

needs 3 or 4 steps to c

116

There was only a trace final product which can be detected by mass spectrum. This may

n groups. Then we had to try

btained in local area.

also be caused by the huge steric hindrance of the substitutio

Route 4. This route gave a surprising good yield (>75%) of final products although the

reaction solvent P(OMe)3 was very smelly and not easy to be o

4.4.2 NMR spectra

117

0.51.01.52.02.53.03.54.04.55.05.56.06.57.07.58.08.5f1 (ppm)

0.51.01.52.02.53.03.54.04.55.05.56.06.57.07.58.0

DiS2F2C

Hb1 Hb2Ha1

Ha2N-CH2-

2F2C

N-CH2-

Ha1 Ha2 Hb1 Hb2

8.5f1 (ppm)

1.01.52.02.53.03.54.04.55.05.56.06.57.07.58.0f1 (ppm)

1.01.52.02.53.03.54.04.55.05.56.06.57.07.58.0f1 (ppm)

DiS2C2T

Ha1 Hb1Ha2

Hb2

N-CH2-

2C2T

Ha1 Ha2 Hb1 Hb2

N-CH2-

impurity

Fig. 4.14 NMR spectrum of five target [2,2]paracyclophanes

119

In dithiaparacyclophanes, the protons of CH2 groups on the cyclophane core bridge can

ot rotate freely because of the ring bridges limitation. The two protons of same bridge

H2 had different chemical environment and can be split by each other. So there are two

ouble splitting peaks at the range of 3.5-4.5 ppm. After removing 2 sulphur atoms from

ridges, [3.3]dithioparacyclophane was changed to [2.2]paracyclophane. All the bridge

H2 protons NMR peaks are removed to the high field and become multiple peaks due to

their splitting by protons on the neighbor CH2 group. Compared five target

[2.2]paracyclophanes with their [3.3]dithiaparacyclophanes precursors, we can see that

all the protons on the final products cores bridges have reduced chemical shifts values

and moved to high fields because of the absence of election-withdrawing sulphur atoms.

These high field chemical shifts and multiple peaks are clear proofs of the forming of

[2.2]paracyclophanes cores.

n

C

d

b

C

R1

R1

R2

R2R1

R2

S

SR1

R2 Hb2

Hb1

Hb2

Hb1

Ha1 Ha2Ha1 Ha2

. .

Fig. 4.15 The different protons on cyclophane core bridge -CH2 groups

4.4.3 MALDI-TOF mass spectrum

All the MALDI-TOF mass spectra of dithia[3.3]paracyclophanes are showed as

follows.

120

77

.27

8

76

9.7

06

15

40

.29

1

61

4.9

40

68

4.8

07

44

5.3

99

52

9.7

78

15

96

.28

9

81

3.0

81

82

5.3

52

14

56

.07

6

0

1000

2000

3000

4000

5000Inte

ns.

[a.u

.]

0 500 1000 1500 2000 2500

m/z

MALDI-TOF mass spectrum of 2F2F

77

.27

9

60

2.6

26

12

06

.91

6

0

500

1000

1500

2000

Inte

ns.

[a.u

.]

0 500 1000 1500 2000 2500

m/z

MALDI-TOF mass spectrum of 2C2C

121

77

.27

9

13

73

.90

7

55

1.2

65

68

5.9

05

79

9.9

52

61

5.9

21

10

44

.49

4

14

29

.50

9

0

1000

2000

3000

Inte

ns.

[a.u

.]

0 500 1000 1500 2000 2500

m/z

MALDI-TOF mass spectrum of 2F2C

77

.27

7

10

38

.57

4

76

9.1

35

0

500

1000

1500

2000

Inte

ns.

[a.u

.]

0 500 1000 1500 2000 2500

m/z

MALDI-TOF mass spectrum of 2F2T

122

77

.27

9

60

1.8

66

87

1.6

55

71

0.7

63

0

250

500

750

1000

1250

Int

s. [a

.u.]

en

0 500 1000 1500 2000 2500

m/z

MALDI-TOF mass spectrum of 2C2T

Fig. 4.16 MALDI-TOF mass spectrum of all final [2.2]paracyclophanes

Compound 2F2F, 2C2C, 2F2C, 2F2T and 2C2T have MALDI-TOF mass spectra at

1540.291, 1206.916, 1373.907, 1038.574 and 871.655. They all have good

correspondence with their molecular weights.

All the spectroscopic properties of the target [2.2]paracyclophanes molecules were

e optical properties are summarized in Table 4.1.


measured in chloroform solution. Th

The representative UV-vis absorption and photoluminescence (PL) are shown in Figure

4.17-21.

123

250 300 350 400 450 500 550 6000.0

0.2

0.4

0.6

0.8

1.0

1.2

0

200

400

600

800

1000

1200

Ab

sorb

an

ce (

No

rma

lize

d)

Wavelength (nm)

DiS2F2F UV 2F2F UV DiS2F2F PL 2F2F PL

PL

Inten

sity (a.u.)

Fig. 4.17 The UV-vis absorption spectra and photoluminescence spectra of DiS2F2F(11) and 2F2F(12) measured from their chloroform solution at room temperature As depicted in Figure 4.17, com rption in 318 nm

(with a shoulder at 279nm) and emission in 382 nm. Compound 2F2F(12) has a UV

absorption in 337 nm (with a sub-peak at 271 nm) and emission in 417 nm. 2F2F(12) has

an 81 nm Stokes shift. Compared with DiS2F2F(11), 2F2F(12) exhibits a 19nm red shift

in UV absorption and 35 nm red shift in PL emission. Its large red shift in PL shows that

2F2F(12) molecule through space interaction was strongly enhanced by removing the

two sulfur atoms from the Dithioparacyclophane core in DiS2F2F(11). In 2F2F(12), the

two benzene rings in the cyclophane were co-facially in close proximity. The [2.2]-

paracyclophane served as a locus of 2 layer’s chromophores contact. By the effective π-π

electron delocalization, 2F2F(12) shows strong combining properties of two layers’

chromophores. This is one of the most important purposes of this synthesis work.

pound DiS2F2F(11) has a Uv abso

124

250 300 350 400 450 500 550 6000.0

0.2

0.4

0.6

0.8

1.0

1.2

0

200

400

600

800

1000

1200

Ab

sorb

anc

e (N

orm

aliz

ed

)

Wavelength (nm)

DiS2C2C UV 2C2C UV DiS2C2C PL 2C2C PL

PL

Inten

sity (a

.u.)

Fig. 4.18 The UV-vis absorption spectra and photoluminescence spectra of DiS2C2C(20) and 2C2C(21) measured from their chloroform solution at room temperature

As depicted in Figure 4.18, compound DiS2C2C(20) has a UV absorption in 301 nm

and emission in 371 nm. Compound 2C2C(21) has a UV absorption in 304 nm (with a

sub-peak at 329 nm) and emission in 419 nm. 2C2C(21) has a 116 nm Stokes shift.

Compared with DiS2C2C(20), 2C2C(21) exhibits a 3 nm red shift in UV absorption and

48 nm red shift in PL emission. Its large red shift in PL shows that [2,2]-paracyclophane

(pCp) core in 2C2C(21) molecule plays a much more important role in through space

interaction than Dithia[3,3]paracyclophane core in DiS2C2C(20).

125

250 300 350 400 450 500 550 6000.0

0.2

0.4

0.6

0.8

1.0

1.2

0

200

400

600

800

1000

1200

Ab

sorb

ance

(N

orm

aliz

ed)

Wavelength (nm)

DiS2F2C UV 2F2C UV DiS2F2C PL 2F2C PL P

L In

tens

ity (a.u

.)

Fig. 4.19 The UV-vis absorption spectra and photoluminescence spectra of DiS2F2C(22) and 2F2C(23) measured from their chloroform solution at room temperature. As depicted in Figure V absorption in 302 nm

UV

sion. Its large red shift in PL shows that

.2]-paracyclophane(pCp) core in 2F2C(23) molecule plays a much more important role

.3]paracyclophane core in DiS2F2C(22).

4.19, compound DiS2F2C(22) has a U

(with a shoulder at 318 nm) and emission in 373 nm. Compound 2F2C(23) has a

absorption in 305 nm (with a sub-peak at 332 nm) and emission in 416 nm. 2F2C(23) has

a 111 nm Stokes shift. Compared with DiS2F2C(22), 2F2C(23) exhibits a 3 nm red shift

in UV absorption and 42 nm red shift in PL emis

[2

in through space interaction than Dithia[3

126

250 300 350 400 450 500 550 6000.0

0.2

0.4

0.6

0.8

1.0

1.2

0

200

400

600

800

1000

1200

Ab

sorb

an

ce (

No

rmal

ized

)

Wavelength (nm)

DiS2F2T UV 2F2T UV DiS2F2T PL 2F2T PL P

L In

tensity

(a.u.)

Fig. 4.20 The UV-vis absorption spectra and photoluminescence spectra of DiS2F2T(28) and 2F2T(29) measured from their chloroform solution at room temperature As depicted in Figure 4.20, compound DiS2F2T(28) has a UV absorption in 303 nm

(with a shoulder at 328 nm) and emission in 368 nm. Compound 2F2T(29) has a UV

absorption in 319 nm and emission in 415 nm. 2F2T(29) has a 97 nm Stokes shift.

Compared with DiS2F2T(28), 2F2T(29) exhibits a 15 nm red shift in UV absorption and


(pCp) core in 2F2T(29) molecule plays a much more important role in through space

interaction than Dithia[3,3]paracyclophane core in DiS2F2T(28).

127

250 300 350 400 450 500 550 6000.0

0.2

0.4

0.6

0.8

1.0

1.2

0

200

400

600

800

1000

1200

Ab

sorb

an

ce (

No

rma

lize

d)

Wavelength (nm)

DiS2C2T UV 2C2T UV DiS2C2T PL 2C2T PL

PL

Inten

sity (a

.u.)

Fig. 4.21 The UV-vis absorption spectra and photoluminescence spectra of DiS2C2T(30) and 2C2T(31) measured from their chloroform solution at room temperature

In conclusion, compared with their Dithia[3,3]paracyclophane core precursor

ompounds, all final [2,2]paracyclophane substituted compounds have large obvious red

ifts(from 35 to 50 nm) in their PL spectrum. These red shifts also make them to have

rge Stokes shifts (from 81 to 127nm). Compound 2C2T has a biggest Stokes shift (127

m) and biggest red shift in PL spectrum compared with its precursor (50 nm), but it has

no red shift in Uv absorption compared with its precursor. For compound 2F2F, it is very

As depicted in Figure 4.21, compound DiS2C2T(30) has a UV absorption in 302 nm

and emission in 379 nm. Compound 2C2T(31) has a UV absorption in 302 nm (with a

sub-peak at 338 nm) and emission in 429 nm. 2C2T(31) has a 127 nm Stokes shift.

Compared with DiS2C2T(30), 2C2T(31) exhibits only no red shift in UV absorption and


(pCp) core in 2C2T(31) molecule plays a much more important role in through space

interaction than Dithia[3,3]paracyclophane core in DiS2C2T.

c

sh

la

n

128

interesting that it has a smallest Stokes shift (81 nm) and smallest red shift in PL

spectrum compared with its precursor (35 nm), but it has a biggest red shift in Uv

absorption compared with its precursor (19 nm).

By removing the two sulfur atoms from the precursor Dithia[3,3]paracyclophane core ,

the nearer two benzene rings co-facial proximity forms a strong π-π delocalization. This

strong π-π delocalization performs dominant effect on their PL and Uv behavior.

Table 4.1 The optical data of [2.2]paracyclophanes and their precursors [3.3]dithioparacyclophane in chloroform solution

Solution λmax(nm)a Eg(eV)b PL Efficiency (%)compound

Abs. Em

DiS2F2F 318 (279) 382 3.52

2F2F 337 (272) 417 3.28 78%

DiS2C2C 301 371 3.87

2C2C 304 (329) 419 3.77 45%

DiS2F2C 302 (318) 373 3.43

2F2C 305 (332) 3.31 63% 416

DiS2F2T 303 (328) 368 3.78

2F2T 319 415 3.49 67%

DiS2C2T 302 379 3.78

2C2T 302 (338) 429 3.66 55%

a. The data in the parentheses are the wavelength of shoulders and sub-peaks; b. Eg stands for the band gap energy estimated from the onset wavelength of the optical absorption.

129


The electrochemical behavior of final substituted cyclophanes and their

dithia[3.3]paracyclophane precursors was investigated by the Cyclic Voltammetry (CV).

The CV was performed in a solution of Bu4NClO4 (0.10M) in chloroform at a scan of 50

mV/s at room temperature under the protection of argon. A platinum electrode was used

as the working electrode. A Pt wire was used as the counter electrode and an Ag/AgNO3

electrode was used as the reference electrode. The corresponding data are summarized in

Figure 4.22-26 and Table 4.2.

-2 -1 0 1 2-6

-4

-2

0

2

8

4

6

I (m

A)

(n

orm

.)

DiS2F2F

E (V vs SCE)

-2 -1 0 1 2-10

-5

0

5

15

10

I (m

A)

(n

Fig. 4.22 The cyclic voltammograms of DiS2F2F(11) and 2F2F(12)

8

o

r

E (V vs SCE)

2F2F

m.)

-2 -1 0 1 2

-6

-4

-2

0

2

4

6

10

DiS2C2C6

8

-1 0 1 2-8

-6

-4

-2

0

2

4

2C2C

I (m

A)

(no

rm.)

E (V vs SCE)

I (m

A)

(no

rm.)

E (V vs SCE)

Fig. 4.23 The cyclic voltammograms of DiS2C2C(20) and 2C2C(21)

130

-2 -1 0 1 2-6

-4

-2

0

2

4

6

8

I (m

A)

(no

rm.)

E (V vs SCE)

DiS2F2C

-2 -1 0 1 2

-4

-2

0

2

4

I (m

A)

(no

rm.)

E (V vs SCE)

2F2C

Fig. 4.24 The cyclic voltammograms of DiS2F2C(22) and 2F2C(23)

0 1 2-2

0

2

6

4

I (m

A

E (V vs SCE)

-2 -1 0 1 2-6

-4

0

) (

DiS2F2T

no

rm.)

2

-2

6

8

4

I (m

A

E (V vs SCE)

8

10

) (

2F2T

Fig. 4.25 The cyclic voltammograms of DiS2F2T(28) and 2F2T(29)

no

rm.)

0 1-2

0

4

6

2

2

IA

) (n

orm

E (V vs SCE)

-2

0

2

-2 -1 0 1 2

4

6

(m

.)

DiS2C2T

I (m

(n

orm

.)

E (V vs SCE)

Fig. 4.26 The cyclic voltammograms of DiS2C2T(30) and 2C2T(31)

A)

2C2T

131

Table 4. 2 The electrochemical data of [2.2]paracyclophanes and their

p-doping (V)

[3,3]dithioparacyclophane precursors in chloroform solution

Energy levels(eV) compound

Eonset Epa Epc HOMO LUMO Eg

DiS2F2F 1.21 1.9 1.40 -5.61 -2.09 3.52

2F2F 0.84 1.04 0.87 -5.24 -1.96 3.28

DiS2C2C 0.80 2.01 1.41 -5.20 -1.33 3.87

2C2C 0.52 1.69 ---- -4.92 -1.15 3.77

DiS2F2C 1.11 1.86 1.53 -5.51 -2.08 3.43

2F2C 0.64 1.49 1.10 -5.04 -1.73 3.31

DiS2F2T 0.88 1.60 0.80 -5.28 -1.50a 3.78

2F2T 0.74 1.80 1.51 -5.14 -1.65 .49 3

DiS2C2T 0.78 1.39 0.82 -5.18 -1.40a 3.78

2C2T 0.71 1.30 0.71 -5.11 -1.45 .66 3

a. LUMO energy calculated by nd HOMO e level

e [2. phane were substituted by electron-donating group such as

thiophene and carbazole, the band gaps were enlarged, which agreed with the spectral

heir hig occupied mole orbital (HOM d the lowest u ccupied

molecular orbital (LUMO) energies had shifted to a higher energy level. These obvious

levels via

tution on the cyclophane core. By changing the substituted chromophores,

the final compounds can have a 0.32 eV change (-5.24 eV to -4.92 eV) in HOMO orbital

level was Eg a nergy

When th 2]paracyclo

blue shift. T hest cular O) an no

differences had well illustrated the adjustable HOMO and LUMO energy

different substi

132

and 0.81 eV change in LUMO orbital (-1.96 eV to -1.15 eV) in the meantime the blue

reaction and UV irradiation reaction, give a guarantee for

the satisfactory yield of whole synthesis route.

Efficient blue light emission, good solubility in common organic solvents had been

demonstrated in all of the five compounds. The optical and electrochemical properties all

exhibited dependence on the changes of different substituted chromophores on the

[2.2]paracyclophane core.

The band gaps of five compounds were varied between 3.28 eV to 3.77 eV.

Modification of the substitution groups on the [2.2]paracyclophane core enabled the

akes the synthesis

route very useful to obtain different [2.2] paracyclophanes derivatives which can be used

in different applications areas such as asymmetric reaction, OLED and NLO materials.

emission are maintained. These changes can still be enhanced by attaching the electron-

withdrawing groups on the cyclophanes core.

4.5 Conclusion

A concise and novel synthesis route was successfully established and five tetra-

substituted [2.2]paracyclophanes were obtained in high yields. Two key step reactions,

which are HBr gas deprotecting

tuning of HOMO and LUMO energy levels. This freely modification m

133

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139

Chapter Five

a ed oligomers are branched macromolecules that consist of linear molecular

together by a central core . Star-shaped oligomers are unique in the sense

combine the properties of the arms with that of the central core (which can have

ensional characters) and this will bring new interesting optoelectronic

Synthesis and Characterization of Hexafluorenyl Benzene

5.1 Introduction

Star-sh p

arms joined 1

that they

one to three dim

o 2

benzene3

these com

serve as potential candidates for OLED

and m rphological properties to the system. Star-shaped oligomers based on truxene and

core with oligofluorenes and thiophene arms(Figure 5.1) have been studied and

pounds are shown to have good optoelectronic properties. These systems thus

, photovoltaics and field transistors.

n

n

n

nn

n

C6H13C6

H13

C H

C3

6H

1

C6H13

C6H13

6 13

=

C6H13 C6H13

S

n

or

Fig. 5.1 Structure of star-shaped oligomers with truxene and benzene core

140

Recently, hexaarylbenzene have attracted immerse interest in the materials community;

nd these

m ar-shaped analogue.

behavio

may ex

dimensions.

“fluore fluorenes are known for their high photoluminescence

propert nt system. In addition, the nature of the side chains at the 9th position

Propyl nyl benzene.

aryl “arms” such as azulene4, pyrene5 and ferrocene6 have been attached a

syste s shows more superior properties than their trisubstituted st

For example, hexakis(azukenyl)benzene was shown to exhibit multielectron redox

r. Hexaarylbenzenes can be thought of as a “double” star-shaped system and this

plain its enhanced properties since the extra three arms add to the multitude of

We thus decide to tap on the potential of such “double” star-shaped system, using

nyl” units as the arms as

efficiency and their ease of chemical transformation. We hope to test the structure and

ies of resulta

of fluorene will be investigated to see if its length (i.e. comparing Methyl group with n-

group and n-Hexyl group) affects the formation of hexafluore


Br Br

R RR R R

Ri ii

R=Hex, 1aR=n-Pr, 1bR=Me, 1c

R=n-Pr, 2bR=Me, 2c

R=Hex, 2a

141

iii

R=Me, 3c

Sche e 5.1 The synthetic routes for target molecule 3c. Reagents and conditions: i. RBr, t-BuO-K+ / DMSO; ii. Trimethylsilylacetylene, Pd(PPh ) Cl CuI

m3 2 2, ,

As o different length of alkyl chains were introduced into the 9-

the fina

fluoren

reaction

he 2b and 2c in 66%, 82%, and

saving ch the

th

a coupling with the original substrate),

three steps of reaction to happen in sequence, using 1, 8- diazabicyclo[5.4.0]undec-7-

ene(DBU) as the base to remove the TMS group. Compared with triethylamine(TEA),

DBU/benzene, 80 oC, 18h; iii. Co2(CO)8 / dioxane, reflux, 24h.

utlined in Scheme 5.1,

position of fluorene. The purpose of adding an alkyl chain is to improve the solubility of

l product in organic solvent and also protect the active protons on 9-position of

e. We also want to explore how the chain lengths affect the cycloaromatization

.

T Brisbois protocol 7 was employed to obtain the 2a,

69% yields respectively. This protocol is advantageous in the sense that it allows the

of two steps reaction compared with the usual procedure (usual one is to atta

trime ylsilylacetyl group via Sonogashira coupling, follow by removal of the TMS

group by a strong base and then another Sonogashir

which save labor and improve yield and atom economy. This one pot protocol allowed all

142

1,4-diazabicyclo[2.2.2]octane (DABCO) and 1,5-Diazabicyclo[4.3.0]non-5-ene (DBN),

DBU was the best choice of base in Brisboi

indicated the amidine base was acting as a proton shuttle. In support of this determination,

orces the invocation of a DBU salt in the organic reaction mixture,8,9

s protocol .The methodology research results

the literature reinf

and DBU has been used catalytically in the nucleophilic addition of acyldiazomethanes to

aldehydes and imines.10 It can be speculated that after proceeding through the commonly

accepted cross-coupling chemistry, the silane-protected aryl-ethynylene converges with

Cu+ and a water/DBU salt, resulting in protodesilylation to yield the terminal ethynylene.

Consequently, the aryl-substituted terminal ethynylene is resubmitted to the cross-

coupling cycle, generating the bisarylethynyl product after a second pass.7

R-Br + H TMSPd(PPh3)2Cl2/CuI

3NEtR TMS

NaOH

MeOH

RBr/NEt3

Pd(PPh3)2Cl2/CuIR H R R

Fig. 5.2 Normal ways to synthesize di-R group substituted alkyne.

The final step of Scheme 5.1 involves cycloaromatization by using Co2(CO)8 as the

catalyst. Only 3c was obtained in 35% yield. The failure of obtaining the 3a and 3b may

indicate that the length of alkyl chains at the 9th position of fluorene has a significant

effect on the formation of the trimerized product. Only the smallest steric hindrance alkyl

group (methyl) can form the final product.

143

The proposed mechanism of cycloaromatization of acetylene using Co2(CO)8 is

illustrated in Scheme 2.11

Co2(CO)8R R

-2CO (OC) Co3 Co(CO)3

R RR R

-CO (OC) Co3 Co(CO)2

R R

R R

R R

(OC)3Co Co(CO)2

R

R

R

R(OC)2Co Co(CO)2

R R

R R(OC)2Co Co

RR

R R

(CO)2

R R

R R

-CO

R R

(OC)2Co Co

RR

(CO)R R

R

RR

.

2R

RR

Fig. 5.3 Proposed mechanism of Cycloaromatization by using Co2(CO)8

Other catalyst system such as Pd/C in THF, PdCl2/CuCl2/BuOH in benzene,

Pd(PPh)3Cl2 in THF and these 3 system working in microwave assisted condition were

also tested for 2a, 2b and 2c. All reactions do not obtain the final product. These results

indicate the steric bulk of the fluorenyl units and the length of side chains makes the

cycloaromatization of flouenen unit a very tough work.

5.3 Results and discussion

5.3.1 NMR spectroscopy

144

118

.16

118

.32

118

.50

119

.53

119

.65

119

.76

122

.21

122

.26

126

.50

126

.61

126

.71

130

.24

130

.51

130

.61

130

.77

26.7

526

.91

Fig. 5.4 1H and 13C spectra of target molecule 3c

145

From the 1H NMR spectrum of target molecule 3c, we can see multiple peaks at about

1.0 ppm. A double split peak at about 27 ppm in 13C spectrum is also found

corresponding to the methyl group on 9-position of fluorene. In addition, there are more

peaks in the 13C NMR spectrum as expected from a symmetrical 3c. (The expanded

aromatic region in the 13C NMR is shown in Figure 5.4). The splitting peaks show a

nonplanarity of molecule 3c. 3c is deduced to be mixture of different conformational

isomers. 3c is expected to be non-planar and a literature search indicates that such

compound tend to take on the shape of a propeller. The cycloaromatization process may

result in the random orientation of the fluorenyl units and thus result in the methyl groups

and some to the carbon atoms being chemically and magnetically non-equivalent. The

broad split signals in some aromatic regions in the 1H spectrum may suggest that 3c is a

conformational mobile system, in which there is some limited bond rotation between the

aryl-aryl single bond at room temperature.

5.3.2 MALDI-TOF mass spectrum

und to have a

omposition of C96H78 (M=1231.4254, Δ=1.80* 10-4). This provides further evidence that

A Maldi-Tof mass was performed and the target compound 3c was fo

c

compound 3c was Hexafluorenyl Benzene.

146

Fig 5.5 MALDI-TOF mass spectrum of target molecule 3c


n was

valuated by thermogravimetric analysis (TGA). 3c shows weight loss at about 220 oC in

o

The thermal stability of the final conformational mixture product 3c in nitroge

e

nitrogen (Figure 5.6). Above 460 C, there is about 30% of residue, which was produced

by charring during heating.

1200 1216 1232 1248 1264 1280

Mass (m/z)

2.3E+4

0

10

20

30

40

50

60

70

80

90

% I

nte

nsi

ty100

Voyager Spec #1=>BC=>AdvBC(32,0.5,0.1)=>NR(2.00)[BP = 1230.4, 23432]

1230.4260

1231.4254

1232.4339

1233.4327

1215.87151230.9148

1257.44681231.11611217.8774

147

100 200 300 400 500 600 700 800

0.2

0.4

0.6

0.8

1.0 3c

Wei

gh

t (%

)

Temperature (OC)

Fig 5.6 The thermogravimetric analysis (TGA) of 3c

Thermally induced phase transition behavior of 3c was also investigated with

differential scanning calorimetry (DSC) in a nitrogen atmosphere. The DSC curve of 3c

is shown in Figure 5.7. From the DSC spectrum, we can see that 3c has a glass transition

temperature (Tg) at 125oC. The relatively low glass transition temperature shows that 3c

could be a conformational mobile system.

148

0 50 100 150 200 250

7

-0.6

-0.2

-0.8

-0.

-0.5

-0.4

-0.3

-0.1

0.0

3c

H/g

)

Temperature (0C)

eat

Flo

w (

W

Fig. 5.7 The DSC trace of 3c


250 300 350 400 450 500

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0

200

400

600

800

1000

1200

Ab

sorb

1c UV 3c UV

an

(N

or

lize

dce

ma

)

Wavelength (nm)

1c PL 3c PL

PL

Inten

sity (a.u.)

Fig. 5.8 The UV-vis absorption spectra and photoluminescence spectra of 3c and 1c measured from their chloroform solution at room temperature

149

The spectroscop were measured

in CHCl3 solution. The optical properties are summarized in Table 5.1

Table 5.1 The optical data and fluorescence quantum yields (both in chloroform solutions) of compound 1c and 3c


ic properties of 3c and 2-Bromo-9, 9-dimethylfluorene

Compound

Abs. Em

1c 275 (309) 321 4.1 25%

3c 323 (282) 356 3.27 8%

a. The data in the parentheses are the wavelength of shoulders and sub-peaks; b. Eg stands for the band gap energy estimated from the onset wavelength of the optical absorption. As depicted in Figure 5.8, compound 3c has a Uv absorption in 323 nm (with a

shoulder at 282nm) and emission in 356 nm. Compound 3c has a 34 nm Stokes shift.

Compared with 1c, target molecule 3c has a 48nm Uv absorption and 35 nm emission

blue shift. The photoluminescence efficiency of 3c is low (8%). This was caused by the

energy lost in transformation of different conformational isomers.

or of compound 3c was investigated by the Cyclic

Voltammetry (CV). The CV was performed in a solution of Bu4NClO4 (0.10M) in

chloroform at a scan of 50 mV/s at room temperature under the protection of argon. A



corresponding data are summarized in Table 5.2.


The electrochemical behavi

150

0 1 2-1

0

1

2

3

4

3c

I (m

A)

(no

rm.)

E (V vs SCE)

Fig. 5.9 The cyclic voltammograms of 3c

Table 5.2 The electrochemical data of the polymers 3c

p-doping (V) Energy levels(eV) compound

aEonset Epa Epc HOMO LUMO Eg

3c 1.43 1.67 1.45 -5.83 -2.56 3.27


5.4 Conclusion

A convenient approach to synthesize hexafluorenyl benzene was successfully

developed. The synthesis was successful for 3c but failed for 3a and 3b. The reason for

the failure may be attributed to the increase in length of the alky chains as we move from

151

methyl to propyl to hexyl group. The increased in length of the alkyl drop may disfavor

the cycloaromatization process because there is an increased steric hindrance.

152

Reference

1. Hadjichristidis, N.; Pitsikalis, M.; Pispas, S.; Iatrou, H. Chem

. Rev. 2001, 101,

. Pei, J.; Wang, J., L.; Cao, X., Y.; Zhou, X., H.; Zhang, W., B. J. Am. Chem. Soc.

, 125, 99

3. Zhou, X., H J., C.; Pei, J . Lett. 2003, 5, 3543.

4.

awakam zawa, A.; T A. J. Org. C 2005, 70, 3939-3949.

, V. J.; Dhar, D.; Lindeman, S. V.; Rathore, R. Organic Letters 2006, 8,

ger, R. J. Org. Chem.

2000, 65, 6202.

10. Jiang, N.; Wang, J. Tetrahedron Lett. 2002, 43, 1285.

3747.

2

2003 44.

.; Yan, . Org

Ito, S.; Ando, M.; Nomura, A.; Morita, N.; Kabuto, C.; Mukai, H.; Ohta, K.;

K i, J.; Yoshi ajiri, hem.

5. Rausch, D.; Lambert, C. Organic Letters 2006, 8, 5037-5040.

6. Chebny

5041-5044.

7. Mio, M. J.; Kopel, L., C.; Braun, J. B.; Gadzikwa, T. L.; Hull, K. L.; Brisbois, R.

G.; Markworth, C. J.; Grieco, P. A. Org. Lett. 2002, 4, 3199.

8. Bordwell, F. G. Acc. Chem. Res. 1998, 21, 456.

9. Kalijurand, I.; Rodima, T.; Leito, I.; Koppel, I. A.; Schwesin

11. G. Inorg. Chim. Acta. 1995, 228, 147.

153

Chapter Six

Experimental Section

6.1 Monomers and Polymers Synthesized in Chapter Two

1,4-Dibromo-2,5-bis(bromomethyl) benzene 2.1

2.6g 1,4-Dibromo-2,5-dimethylbenzene (2.6g, 10 mmol), NBS (3.9g, 22mmol) and a

catalytic amount of benzoyl peroxide were mixed in carbon tetrachloride (100 ml). The

suspension was refluxed under irradiation for 4h. After the reaction mixture was cooled

to room temperature, 300 ml methylene chloride was added in and did the filtration to

remove the inorganic salts. The filtrate was washed with water (150ml x 3) and brine

drous magnesium sulfate. After

ltration, the solvent was removed by rotary evaporation to give white solid. The crude

%) white crystal

solid. 1H NMR (CDCl3, 300 MHZ, ppm) δ 7.64 (s, 2H), 4.49 DCl3,

75.5MHZ, ppm δ 1 8.96, 13 3 , 123.26 1 5. MS ): 4 .

1,4-Dibromo-2,5-bis(methoxymethyl)benzene 3.2

Sodium (1.16 g, 50 mmol) was added slowly to methanol (100 ml) under nitrogen with

cooling bath was

moved. 1,4-Dibromo-2,5-bis(bromomethyl)benzene (4.22 g, 10 mmol) in THF was

ly and the mixture was refluxed for 12 h. When the reaction was

through a short silica gel column using hexane and methylene chloride (5:1) as eluant to

(150ml). The organic mixture was dried over anhy

fi

product was recrystallized twice from ethanol to give 2.7g (Yield: 65

(s, 4H). 13C NMR (C

): 3 5. 3 , 3 .4 (EI, m/z 21.0 (M+)

water-bath cooling. When the vigorous reaction moderated, the

re

then added slow

completed, water was added in. The mixture was extracted three times with ether and

washed sequentially with water and brine. The organic layer was dried over anhydrous

magnesium sulfate and evaporated to give a yellow residue. The residue was passed

154

give 3.04 g (Yield: 94%) white solids. Mp: 75-77 C. 1H NMR (CDCl3, 300MHz, ppm):

7.63 (s, 2H), 4.47 (s, 4H), 3.47 (s, 6H). 13C NMR (CDCl3, 75.5 MHz, ppm): 138.3,

132.2, 121.1, 73.1, 58.7. MS (EI, m/z): 324.

2-bromo-9, 9-di-n-hexylfluorene 5. 3

A solution of 1-bromohexane (12.7g, 77mm ) in DMSO (15ml) was added to a mixture

of 2-bromofluorene (7.6g, 31 mmol), a catalyst amount of tetrabutylammonium bromide

and 50 % (w/w) aqueous NaOH (12ml) in DMSO (60 ml). The reaction mixture was

cooled to room temperature and stirred for 12 hours. 300 ml Dichloromethane was added

in. The mixture was extracted by water (150ml x 5) to remove the DMSO and salt. Rotar

evaporator was used to remove the organic solvent. Pure hexane was used to run the

silica gel column to obtain the colorless oil product. Yield: 10.3 g (90%). 1H NMR

(CDCl3, 300 MHZ, ppm) δ 7.69-7.33 (m, 7H), 1.99-1.85(m, 4H), 1.33-0.60(m, 22H). 13C

NMR(CDCl3, 75.5MHZ, ppm) δ 152.98, 150.31, 140.14, 140.03, 130.15, 127.43, 126.90,

126.14, 122.86, 121.09, 120.98, 119.72, 55.36, 40.28, 31.45, 29.63, 23.67, 22.54, 13.94.

MS (EI, m/z): 412.1(M+).

9, 9-di-n-hexylfluorene-2-bronic acid 6.4

A solution of BuLi (9.8ml, 15.7mmol, 1.6M in hexane) in THF was added slowly into

a stirring mixture of 2-bromo-9,9-di-n-hexyl luorene (5.0g, 12.1mmol) and 50 ml THF

under nitrogen at -78 oC. After keeping at this temperature for 2 hours, trimethyl borate

(2.8g, 24mmol) was added. The reaction mixture was stirred for 24 hours to room

temperature. The mixture was poured into crushed ice containing sulfuric acid (5%)

ol

f

155

while stirring. The mixture was extrac yl acetate and the combined extracts

hexane – acetone (1:2) afforded 2.2g (50%) white solid. This solid was used directly to

, 9

propan anic

ure was dried over

evaporation to give colorless oil. The crude product was purified by column

oma

(Yield: ), 7.36-7.31(m, 3H),

2(t, (m, 22H). 13C NMR (CDCl3,

122.83, 119.92, 118.81, 61.96, 54.90, 40.37, 31.49, 29.72, 27.42, 23.69, 22.57, 13.97. MS

m/

,4-bis (9, 9-di-n-hexylfluorenyl)-2,5-bis(methoxymethyl) benzene 8.

To a 100 ml one neck flask was added 9,9-di-n-hexylfluorene-2- trimethylene boronate

.73g, 16 mmol), 1, 4 – Dibromo – 2,5- bis(bromomethyl) benzene(2.17 g, 6.7 mmol),

atalytic amount of Bu4NBr and 40 ml toluene. Once all the monomers were dissolved,

7 ml 2 M Na2CO3 aqueous solution was added. The flask equipped with a condenser

ted with eth

were evaporated to give a yellow solid. Recrystallization of the crude product from

next step without characterization.

9, 9-di-n-hexylfluorene-2- trimethylene boronate 7.5

9 -di-n-hexylfluorene-2-bronic acid (2.0g, 5.3mmol) was refluxed with 1, 3-

diol (1.0 g, 16.5 mmol) in 50 ml toluene for 12h. After working up, the org

layer was washed with water (50ml x 2) and brine. The organic mixt

anhydrous magnesium sulfate. After filtration, the solvent was removed by rotary

chr tography eluting with 50% dichloromethane in hexanes to yield 1.9g colorless oil

88%). 1H NMR (CDCl3, 300 MHZ, ppm) δ 7.82-7.7(m, 4H

4.2 J=5.6HZ, 4H), 2.11-1.94(m, 6H), 1.16-0.61

75.5MHZ, ppm) δ 151.23, 149.66, 143.49, 141.08, 132.40, 127.78, 127.21, 126.57,

(EI, z): 418.4(M+).

1

(6

c

2

156

was then evacuated and filled wit imes to remove traces of air. Pd

(PPh3)4 (155 mg, 2% mmol) was then added un osphere. The flask

was again evacuated and filled with nitrogen three times. The reaction mixture was then

ixture was then

l water. The resulting mixture was

3

3.61 mmol) in 100 ml CHCl3

2 3

3

h nitrogen three t

der the nitrogen atm

heated to 95 – 100 oC and maintained for 48 h under nitrogen. The m

cooled to room temperature and poured into 100m

extracted with ether (80ml x 3) and the combined organic extracts were washed with

water and brine. The organic mixture was dried over anhydrous magnesium sulfate.

After filtration, the solvent was removed by rotary evaporation to give a colorless liquid.

The product was purified by column chromatography (eluent: n-hexane/ ethyl acetate = 6:

1) to offer 3.9 g (yield: 70%) white solid. 1H NMR (CDCl , 300 MHZ, ppm) δ 7.78-

7.73(m, 4H), 7.59(s, 2H), 7.45-7.23(m, 10H), 4.43(m, 4H), 3.38(m, 6H), 2.03-1.98(m,

8H), 1.14-1.07(m, 24H), 0.79-0.65(m, 20H). MS (EI, m/z): 831.0 (M+).

1,4-bis (9, 9-di-n-hexylfluorenyl)-2,5-bis(bromomethyl) benzene 9.

HBr gas was bubbled vigorously through a solution of 1, 4-bis (9, 9-di-n-

hexylfluorenyl)-2, 5-bis (methoxymethyl) benzene (3.0g,

for 20 minutes. The reaction mixture was stirred for an additional 20h in room

temperature and neutralized with 2 M Na CO aqueous solution. The organic layer was

washed with water (100ml x 3) and brine. Then it was dried over anhydrous magnesium

sulfate. After filtration, the solvent was removed by rotary evaporation to give a pale

yellow solid (3.18g, Yield, 95%) without further purification. . 1H NMR (CDCl , 300

MHZ, ppm) δ 7.88-7.74(m, 4H), 7.57-7.54(m, 4H), 7.43-7.26(m, 8H), 4.50(s, 4H), 2.05-

2.00(m, 8H), 1.16-1.11(m, 24H), 0.79-0.67(m, 20H). MS (ESI, m/z): 928.2(M+).

157

Poly[2,5-di(9,9-dihexylfluorene-2-yl)-1,4-phenylenevinylene] 10.

A solution of 1, 4-bis (9, 9-di-n-hexylfluorenyl)-2, 5-bis (bromomethyl) benzene (9)

67mg, 0.4mmol) in 15 ml anhydrous THF was added to a solution of 1M potassium

rred in room temperature under the protection of

nd brine (150ml) to remove most of the DMF. The organic

ixture was dried over anhydrous magnesium sulfate. After filtration, the solvent was

ight brown solid. Do the recrystallization in

(3

tert-butoxide (3ml). The mixture was sti

nitrogen for 24 hours. After that, the mixture was poured into 250ml of methanol with

stirring. The resulting green yellow precipitate was collected by filtration and redissolved

in chloroform and reprecipitated in methanol for two times. The solid was extracted

through Soxhlet extractor with methanol for 24 hours and finally dried under vacuum to

afford 167 mg (Yield: 55%) yellow green polymer.

3-Bromo carbazole 12.6

Carbazole (3.60 g, 1.6 mmol) was dissolved in 60 ml DMF in a 100ml flask. NBS

(3.84g, 21.6 mmol) was added in. The reaction mixture was heated to 80 oC and stirred

for 12h. 150 ml chloroform was added in to the flask. The resulting mixture was washed

with water (150ml x 4) a

m

removed by rotary evaporation to give a l

methanol to obtain 3.82 g (Yield: 72%) white product. 1H NMR (300 MHz, DMSO-d6) δ

11.42 (s, 1H), 8.33 (s, 1H), 8.12 (d, 1H, J = 7.7 Hz), 7.52-7.41 (m, 4H), 7.14 (t, 1H, J =

7.3 Hz,). 13C NMR (DMSO-d6, 75.5MHZ, ppm) δ 140.1, 138.0, 127.7, 126.5, 124.2,

122.9, 121.3, 120.5, 118.8, 112.8, 111.5, 110.3. MS (EI, m/z): 245.0(M+).

158

3-Bromo-N-hexyl-carbazole 13.6

3-bromo- carbazole (1.93g, 7.84 mmol) was dissolved in 50 ml DMSO. KOH (0.48g,

8.62 mmol) was added into the solution. After stirring 30 minutes, n- bromohexane was

added (1.43 ml, 10mmol). The resulting mixture was heated to 50 oC and stirred for 10h.

50 ml chloroform was added into the mixture. The resulting mixture was washed with

f the DMF. The organic mixture

e 1.6 M n-BuLi in hexane (6.5 ml, 10.40 mmol) under nitrogen.

he resulting mixture was stirred for 1h while maintaining the temperature at -78 oC,

l, 20.8 mmol)

1

water (100ml x 4) and brine (150ml) to remove most o

was dried over anhydrous magnesium sulfate. After filtration, the solvent was removed

by rotary evaporation to give a brown solid. Do the recrystallization in methanol to obtain

2.33g (Yield: 90%) white product. 1H NMR (CDCl3, 500 MHZ, ppm) δ 8.24 (s, 1H),

8.08-8.07 (d, 1H, J = 7.6 HZ), 7.58-7.51 (m, 2H), 7.44-7.42 (m, 1H), 7.31-7.26 (m, 2H),

4.29-4.26 (t, 2H, J = 7.25 HZ), 1.90-1.85 (m, 2H), 1.41-1.30 (m, 6H), 0.92-0.90 (t, 3H, J

= 6.63 HZ). 13C NMR (CDCl3, 125MHZ, ppm) δ 140.74, 139.09, 128.22, 126.34, 124.59,

123.08, 121.84, 120.54, 119.20, 111.52, 110.12, 108.94, 43.22, 31.57, 28.89, 26.95, 22.55,

14.01. MS (EI, m/z): 329.1(M+).

N-hexyl-3-(4,4,5,5-tetramethyl-1,3,2-dioxoborolanyl)-carbazole 14.7

To a solution of 3-bromo-N-hexyl-carbazole (2.45g, 7.42 mmol) in THF (50 ml) at -78

oC was added dropwis

T

after which 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (4.2m

was added and the mixture was stirred at -78 oC for an additional hour. The reaction

mixture was then allowed to warm to room temperature and stirred for 24h. The mixture

was then cooled to 0 oC and 2N HCl (40ml) was added in. After the mixture was stirred

for 10 minutes, it was extracted with diethyl ether (100ml x 2). The organic layer was

159

washed with water and dried over anhydrous magnesium sulfate. After filtration, the

solvent was removed by rotary evaporation to give a brown viscous liquid. The crude

product was purified by column chromatography (eluent: n-hexane/ ethyl acetate = 30: 1)

to obtain a yellow liquid. (2.07g, Yield: 74%) 1H NMR (CDCl3, 500 MHZ, ppm) δ 8.70(s,

1H), 8.23-8.21(d, 1H, J= 10HZ), 8.02-8.00(d, 1H, J=10 HZ), 7.54-7.51(m, 1H), 7.51-

7.45(m, 2H), 7.33-7.28(m, 1H), 4.35-4.32(t, 2H, J=7.5 HZ) 1.94-1.88(m, 2H),

1.48(s,12H), 1.44-1.32(m, 6H), 0.95-0.92(t, 3H, J=7.5 HZ). 13C NMR(CDCl3, 125MHZ,

ppm) δ 142.55, 140.47, 132.05, 127.71, 125.53, 123.06, 122.55, 120.48, 119.13, 108.66,

108.02, 83.48, 43.00, 31.50, 28.83, 26.86, 24.88, 22.45, 13.94.

1,4-bis (N-hexylcarbazole-3-yl)-2, 5-bis(methoxymethyl) benzene 15.

To a 100 ml one neck flask was added N-hexyl-3-(4,4,5,5-tetramethyl-1,3,2-

ioxoborolanyl)-carbazole (1.40g, 3.7 mmol), 1,4-Dibromo-2,5- bis(bromomethyl)

luene. Once all the

ation to

d

benzene (0.50 g, 1.5 mmol), catalytic amount of Bu4NBr and 40 ml to

monomers were dissolved, 27 ml 2 M Na2CO3 aqueous solution was added. The flask

equipped with a condenser was then evacuated and filled with nitrogen three times to

remove traces of air. Pd (PPh3)4 (36 mg, 2% mmol) was then added under a nitrogen

atmosphere. The flask was again evacuated and filled with nitrogen three times. The

reaction mixture was then heated to 95 – 100 oC and maintained for 72 h under nitrogen.

The mixture was then cooled to room temperature and poured into 100ml water. The

resulting mixture was extracted with ether (80ml x 3) and the combined organic extracts

were washed with water and brine. The organic mixture was dried over anhydrous

magnesium sulfate. After filtration, the solvent was removed by rotary evapor

160

give a brown liquid. The product was purified by column chromatography (eluent: n-

NMR (CDCl3, 500

yl) benzene 16.

HBr gas was bubbled vigorously through a solution of 2.50g (3.76 mmol) 1, 4-bis (N-

bis (bromomethyl) benzene in 100 ml CHCl3 for 20 minutes.

.07.

hexane/ ethyl acetate = 30: 1) to offer 0.73 g solid (yield: 71%). 1H

MHZ, ppm) δ 8.31-8.30 (d, 2H, J= 1.85 HZ), 8.21-8.19 (d, 2H, J = 8.20 HZ), 7.37 (s, 2H),

7.68-7.66 (m, 2H), 7.57-7.49 (m, 6H), 7.33-7.30 (t, 2H, J = 7.25 HZ), 4.56 (s, 4H), 4.42-

4.39 (t, 4H, J = 7.25 HZ), 2.00-1.94 (m, 4H), 1.52-1.39 (m, 12H), 0.97-0.95 (t, 6H, J =

7.25 HZ). 13C NMR(CDCl3, 75.5MHZ, ppm) δ 141.47, 140.90, 139.76, 135.01, 131.60,

131.29, 127.30, 125.79, 123.00, 122.77, 121.22, 120.43, 118.93, 108.85, 108.23, 72.79,

58.27, 43.30, 31.67, 29.09, 27.10, 22.65, 14.10.

1,4-bis (N-hexylcarbazole-3-yl)-2,5-bis(bromometh

hexylcarbazole-3-yl)-2, 5-

The reaction mixture was stirred for an additional 20h and neutralized with 2 M Na2CO3

aqueous solution. The organic layer was washed with water (100ml x 3) and brine. Then

it was dried over anhydrous magnesium sulfate. After filtration, the solvent was removed

by rotary evaporation to give a pale blue solid (2.54g, Yield, 89%) without further

purification. 1H NMR (CDCl3, 500 MHZ, ppm) δ 8.31-8.30 (d, 2H, J = 1.25 HZ), 8.19-

8.18 (d, 2H, J = 7.6 HZ), 7.69-7.67 (m, 2H), 7.65 (s, 2H), 7.56-7.48 (m, 6H), 7.31-7.29 (t,

2H, J = 6.93 HZ), 4.62 (s, 4H), 4.41-4.38 (t, 4H, J = 7.25 HZ), 1.99-1.94 (m, 4H), 1.51-

1.34 (m, 12H), 0.94-0.91 (t, 6H, J = 7.25 HZ). 13C NMR(CDCl3, 125MHZ, ppm) δ

142.17, 140.92, 139.91, 135.79, 133.63, 130.02, 126.72, 125.97, 122.90, 122.76, 120.90,

120.57, 119.04, 108.88, 108.54, 43.32, 32.38, 31.64, 29.04, 27.06, 22.60, 14

161

Poly[2,5-di(N-hexylcarbazol-3-yl)-1,4-phenylenevinylene] 17.

90 ml) under stirring at room temperature. The reaction

Cl solution. The

A solution of 1, 4-bis (N-hexylcarbazole-3-yl)-2, 5-bis (bromomethyl) benzene (16)

(326mg, 0.43mmol) in 13 ml anhydrous THF was added to a solution of 1M potassium

tert-butoxide (3ml). The mixture was stirred in room temperature under the protection of

nitrogen for 24 hours. After that, the mixture was poured into 250ml of methanol with

stirring. The resulting green yellow precipitate was collected by filtration and redissolved

in chloroform and reprecipitated in methanol for two times. The solid was extracted

through Soxhlet extractor with methanol for 24 hours and finally dried under vacuum to

afford 127 mg (Yield: 51%) yellow green polymer.

6.2 Monomers and Polymers Synthesized in Chapter Three

2,7-Dibromofluoren-9-one 2.8

CrO3 (4.8g, 48 mmol) was added to a suspension of 2,7-dibromofluorene ( 6.38 g,

19.72 mmol) in acetic anhydride (

mixture was stirred for 5 h. The mixture was poured into 1000ml 2% H

suspension was filtered off and washed with cold water. The product was recrystallized in

methanol to provide 6.0 g (90%) of the title product as a yellow solid. Mp 202-204 °C;

mp(lit.) 203-205 °C. 1H NMR (CDCl3, 500 MHZ, ppm) δ 7.80-7.79 (d, 2H, J= 1.9Hz);

7.66-7.65 (q, 2H, J= 1.25HZ and 1.9 HZ); 7.42-7.41 (d, 2H, J= 7.55 HZ). 13C

NMR(CDCl3, 125MHZ, ppm) δ 190.92, 142.28, 137.47, 135.31, 127.87, 123.33, 121.83.

MS (EI, m/z): 337.8(M+).

9-(9H-fluoren-9-ylidene)-2,7-dibromo-9H-fluorene 4.9

162

Fluorene (735mg, 4.42mmol) was dissolved in 30 ml of THF under argon and cooled

to -78 oC. n-Butyllithium (1.6M in hexane, 3.6ml, 5.75mmol) was added. After the

solution was stirred for 10 minutes, trimethylsilyl chloride (0.56ml, 4.42mmol) was

added, and the solution was stirred for an additional 10 minutes. A second portion n-

Butyllithium (1.6M in hexane, 3.0ml, 4.86mmol) was added, and the solution was stirred

for 7 minutes. 2, 7-Dibromofluoren-9-one (2) (1.49g, 4.42mmol) in 30ml of THF was

added, and the solution was allowed to warm to room temperature and to stir overnight.

After the reaction was completed, 75ml water and saturated NH4Cl were added, and the


ere washed with water (100ml x 2) and brine. The organic mixture was dried over

oved by rotary

w

anhydrous magnesium sulfate. After filtration, the solvent was rem

evaporation to give an orange red solid. Recrystallization was made in hexane to obtain

1.50g (Yield: 70%) orange red product. 1H NMR (CDCl3, 500 MHZ, ppm) δ 8.51-8.50(d,

2H, J=1.9 HZ), 8.30-8.28(d, 2H, J=8.2 HZ), 7.71-7.69(d, 2H, J=7.6 HZ), 7.56-7.54(d, 2H,

J=8.2 HZ), 7.48-7.46(dd, 2H, J=1.9 and 1.9 HZ), 7.40-7.37(m, 2H), 7.28-7.25(m, 2H).

13C NMR (CDCl3, 125MHZ, ppm) δ 143.72, 141.84, 139.65, 138.82, 138.00, 137.67,

131.75, 130.18, 120.10, 127.33, 126.77, 121.07, 120.87, 120.18. MS (EI, m/z):

486.2(M+).

2,7-dibromo-9,9-di-n-hexylfluorene 5.10

A solution of 1-bromohexane (12.7g, 77mmol) in DMSO (15ml) was added to a

mixture of 2, 7-dibromofluorene (10.0g, 31 mmol), a catalyst amount of

tetrabutylammonium bromide and 50 % (w/w) aqueous NaOH (12ml) in DMSO(60 ml).

163

The reaction mixture was cooled to room temperature and stirred for 12 hours, 300 ml

dichloromethane was added, the mixture was extracted by water (150ml x 5) to remove

most of the DMSO and salt, rotary evaporator was used to remove the organic solvent,

pure hexane was used to run the silica gel column to obtain the colorless solid product.

Yield: 14.2 g (93%). Mp: 65-66 oC. 1H NMR (CDCl3, 300 MHZ, ppm) δ 7.52-7.47(m,

4H), 7.44-7.43(m, 2H), 1.93-1.87(m, 4H), 1.16-1.03(m, 12H), 0.75(t, 6H, J=7.0 HZ),

0.60-0.58(m, 4H). 13C NMR(CDCl3, 125MHZ, ppm) δ 152.55, 139.00, 130.11, 126.20,

121.40, 121.09, 55.61, 40.12, 31.49, 29.56, 23.60, 22.50, 13.94. MS (EI, m/z): 492.0(M+).

ith 1,3-

ropandiol (2.0 g , 33.0 mmol) in 50 ml toluene for 12h. After working up, 50 ml water

9, 9-di-n-hexylfluorene-2,7-dibronic acid 6.5

A solution of BuLi (19.6ml, 31.4mmol, 1.6M in hexane) in THF was added slowly into

a stirring mixture of 6.0g (12.1mmol) 2, 7-dibromo-9, 9-di-n-hexylfluorene and 50 ml

THF under nitrogen at -78 oC. After keeping at this temperature for 2 hours, 5.6g

trimethyl borate (48mmol) was added. The reaction mixture was stirred for 24 hours to

room temperature. The mixture was poured into crushed ice containing sulfuric acid (5%)

while stirring. The mixture was extracted with ethyl acetate and the combined extracts

were evaporated to give a yellow solid. Recrystallization of the crude product from

hexane – acetone (1:2) afforded 3.0g (61%) white solid. This solid was used directly to

next step without purification and characterization.

9,9-di-n-hexylfluorene-2,7- bis(trimethylene boronate) 7.5

9,9-di-n-hexylfluorene-2,7-dibronic acid (2.2g, 5.3mmol) was refluxed w

p

164

was added and the resulting mixture was extracted with ether (50ml x 2) and the

, 27.43, 23.69, 22.62, 13.99. MS

I, m/z): 502.0(M+).

thyl-1,3,2–dioxoborolane-2-yl)-carbazole 11.

ith water and dried over anhydrous magnesium sulfate. After

ltration, the solvent was removed by rotary evaporation to give a brown viscous liquid.

aphy (eluent: n-hexane/ ethyl

combined organic extracts were washed with water and brine. The organic mixture was

dried over anhydrous magnesium sulfate. After filtration, the solvent was removed by

rotary evaporation to give some colorless oil. The crude product was purified by column

chromatography eluting with 50% dichloromethane in hexanes to yield 2.3g (Yield: 88%)

white solid. 1H NMR (CDCl3, 500 MHZ, ppm) δ 7.77-7.67(m, 6H), 4.22-4.19(t, 8H,

J=5.39HZ), 2.11-2.07(m, 4H), 2.01-1.96(m, 4H), 1.11-1.00(m, 12H), 0.76-0.71(t, 6H,

J=6.98HZ), 0.56-0.53(m, 4H). 13C NMR (CDCl3, 125MHZ, ppm) δ 150.28, 143.51,

132.30, 127.84, 119.14, 62.00, 54.86, 40.36, 31.54, 29.77

(E

N-hexyl-3,6-bis(4,4,5,5-tetrame

To a solution of 3, 6-Dibromo-N-hexyl-carbazole (1.16g, 2.84 mmol) in THF (50 ml)

at -78 oC was added dropwise n-BuLi (5.33mL, 8.52 mmol, 1.6 M in hexane) solution

under nitrogen. The resulting mixture was stirred for 1h while maintaining the

temperature at -78 oC, after which 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane

(2.9 mL, 14.2 mmol) was added and the mixture was stirred at -78 oC for an additional

hour. The reaction mixture was then allowed to warm to room temperature and stirred for

24h. The mixture was then cooled to 0 oC and 2N HCl (40ml) was added in. After the

mixture was stirred for 10 minutes, it was extracted with diethyl ether (100ml x 2). The

organic layer was washed w

fi

The crude product was purified by column chromatogr

165

acetate = 30: 1) to obtain a yellow liquid. (0.93g, Yield: 65%) 1H NMR (CDCl3, 300

MHZ, ppm) δ 8.56(s, 2H), 7.80-7.77(dd, 2H, J=1.2 HZ), 7.27-7.24(dd, 2H, J=0.6 HZ),

4.17-4.13(t, 2H, J=7.2 HZ), 1.80-1.70(m, 2H), 1.26(s, 24H), 1.20-1.11(m, 6H), 0.80-

0.65(m, 3H). (EI, m/z): 503.2(M+).

Poly[9-(9H-fluoren-9-ylidene)-2,7-fluorenyl]-co-alt-2,7-(9,9-dihexylfluorene) P1.

To a 50 ml one neck flask was added 9-(9H-fluoren-9-ylidene)-2,7-dibromo-9H-

fluorene(4) (124mg, 0.26 mmol), 9, 9-di-n-hexylfluorene-2, 7- bis(trimethylene

boronate)(7) (128mg, 0.26 mmol), catalytic amount of Bu4NBr and 20 ml toluene. Once

all the monomers were dissolved, 15 ml 2 M Na2CO3 aqueous solution was added. The

flask equipped with a condenser was then evacuated and filled with nitrogen three times

to remove traces of air. Pd (PPh3)4 (12 mg, 4% mmol) was then added under a nitrogen

atmosphere. The flask was again evacuated and filled with nitrogen three times. The

reaction mixture was then heated to 95 – 100 oC and maintained for 72 h under nitrogen.

The mixture was then cooled to room temperature and poured into 200ml of methanol

with stirring. The resulting brown yellow precipitate was collected by filtration and

redissolved in chloroform and reprecipitated in methanol for two times. The solid was

extracted through Soxhlet extractor with methanol for 24 hours and finally dried under

acuum to afford 78 mg (Yield: 45%) brown yellow polymer. v

Poly[9-(9H-fluoren-9-ylidene)-2,7-fluorenyl]-co-alt-3,6-(N-hexylcarbazole) P2.

To a 50 ml one neck flask was added 9-(9H-fluoren-9-ylidene)-2,7-dibromo-9H-

fluorene(4) (483mg, 0.99 mmol), N-hexyl-3,6-bis(4,4,5,5-tetramethyl-1,3,2–

166

dioxoborolane-2-yl)-carbazole (11) (500mg, 0.99 mmol), catalytic amount of Bu4NBr

and 30 ml toluene. Once all the monomers were dissolved, 22 ml 2 M Na2CO3 aqueous

solution was added. The flask equipped with a condenser was then evacuated and filled

with nitrogen three times to remove traces of air. Pd (PPh3)4 (12 mg, 4% mmol) was then

added under a nitrogen atmosphere. The flask was again evacuated and filled with

nitrogen three times. The reaction mixture was then heated to 95 – 100 oC and maintained

for 72 h under nitrogen. The mixture was then cooled to room temperature and poured

into 400ml of methanol with stirring. The resulting brown yellow precipitate was

collected by filtration and redissolved in chloroform and reprecipitated in methanol for

hlet extractor with methanol for 24 hours

3) and the combined organic extracts

ere washed with water and brine. The organic mixture was dried over anhydrous

d by rotary evaporation to

two times. The solid was extracted through Sox

and finally dried under vacuum to afford 348 mg(Yield: 61%) brown yellow solid.

6.3 Molecules Synthesized in Chapter Four

2, 5-bis (9, 9-di-n-hexylfluoren-2-yl)-1, 4-bis (mercaptomethyl)benzene 10.

A solution of 1,4-bis (9,9-di-n-hexylfluorenyl)-2,5- bis(bromomethyl)benzene (623mg,

0.67mmol) and thiourea (153mg, 2.00mol) in 40 ml ethanol and 20 ml hexane was

refluxed for 2 h. Then KOH (0.3g, 5.40mmol) in 2ml water was added for another 2h

refluxing. After the reaction mixture was cooled down, 50ml 2N HCl was added. The

resulting mixture was extracted with ether (70ml x

w

magnesium sulfate. After filtration, the solvent was remove

give a viscous brown solid. The product was purified by silica gel column

chromatography (eluent: n-hexane/ ethyl acetate = 4: 1) to afford a brown liquid (364mg,

167

Yield: 65%). 1H NMR (CDCl3, 500 MHZ, ppm) δ 7.83-7.78(dd, 4H, J=7.60 and 6.95

HZ), 3.80-3.78(d, 4H, J=7.55 HZ), 2.07-2.03(m, 8H), 1.80-1.76(t, 2H, J=7.25HZ), 1.19-

1.05(m, 24H), 0.82-0.71(m, 20H). 13C NMR(CDCl3, 125MHZ, ppm) δ 150.94, 141.45,

140.72, 140.50, 138.93, 137.72, 131.41, 127.77, 127.21, 126.85, 123.79, 122.92, 119.80,

119.64, 55.21, 40.48, 31.55, 29.74, 26.52, 23.88, 22.59, 14.01.

5, 8, 14, 17-tetra (9, 9-di-n-hexylfluoren-2-yl) dithia[3.3]paracyclophane 11.

A solution of 2, 5-bis(9,9-di-n-hexylfluoren-2-yl)-1,4-bis(mercaptomethyl)benzene(10)

(321mg, 0.384mmol) and 1,4-bis (9, 9-di-n-hexylfluorenyl)-2,5-bis(bromomethyl)

benzene(9)(356mg, 0.384mmol) in 80 ml degassed toluene was added dropwise with

irring to a solution of KOH(431mg, 7.68mmol) in 300 ml ethanol and 100 ml hexane.

at room

st

After the addition was completed, the reaction mixture was stirred for 48h

temperature under the protection of nitrogen. The organic solvent was removed under

reduced pressure and 100 ml chloroform was added to dissolve the residue. The resulting

mixture was washed with water (100ml x 2) and brine. The organic mixture was dried

over anhydrous magnesium sulfate. After filtration, the solvent was removed by rotary

evaporation to give a pale solid. The crud product was purified by column

chromatography (eluent: n-hexane/ ethyl acetate = 1: 300) to afford 320mg (Yield: 52%)

pale yellow liquid. 1H NMR (CDCl3, 300 MHZ, ppm) δ 7.73-7.65(m, 4H), 7.50-7.26(m,

28H), 4.30-4.25(d, 4H, J=15HZ), 3.90-3.85(d, 4H, J=15HZ), 1.97-1.94(m, 16H), 1.10-

0.95(m, 48H), 0.77-0.67(m, 40H). 13C NMR(CDCl3, 75.5MHZ, ppm) δ 150.88, 150.77,

140.84, 140.22, 140.00, 139.48, 133.55, 132.06, 128.20, 126.98, 126.73, 124.32, 122.85,

168

119.84, 119.68, 55.14, 40.61, 40.47, 33.52, 31.59, 31.49, 29.82, 29.78, 23.88, 22.69,

13.96. MALDI-TOF: 1602.431

4, 7, 12, 15-tetra (9, 9-di-n-hexylfluoren-2-yl) [2.2]paracyclophane 12.

5, 8, 14, 17 - tetra (9, 9-di-n-hexylfluoren-2-yl) dithia [3.3]paracyclophane(11) (200mg,

lask

, 5-bis (N-n-hexylcarbazole -3-yl)-1, 4-bis (mercaptomethyl)benzene 19.

e(16)

0.13mmol) was dissolved in 50ml trimethyl phosphate in 100ml conical flask. The f

was put into a UV reactor (Hg, 180 W) and was irradiated for 24 h in room temperature.

The trimethyl phosphate was removed in vacuum. The resulting mixture was added

100ml chloroform and washed with water and brine. The organic mixture was dried over


evaporation to give a yellow brown solid. The crude product was purified by column

chromatography (eluent: n-hexane/ ethyl acetate = 300: 1) to obtain a colorless liquid(170

mg, Yield: 88%). 1H NMR (500 MHz, CDCl3) δ 7.85-7.70(m, 8H), 7.62(s, 4H), 7.45-

7.35(m, 16H), 7.08-7.07(d, 4H, J=3.8 HZ), 3.69-3.63(m, 4H), 2.94-2.88(m, 4H), 2.04-

2.01(m, 16H), 1.15-0.98(m, 48H), 0.79-0.70(m, 40H). 13C NMR(CDCl3, 75.5MHZ, ppm)

δ 150.95, 150.91, 140.90, 140.39, 139.93, 139.49, 137.12, 132.29, 127.50, 126.98, 126.78,

123.94, 122.87, 119.84, 119.77, 55.12, 40.62, 40.45, 33.71, 31.55, 29.76, 23.93, 23.84,

22.56, 22.50, 13.97, 13.95. MALDI-TOF: 1538.154.

2

A solution of 1,4-bis (N-hexylcarbazole-3-yl)-2,5-bis(bromomethyl) benzen

(993mg, 1.31mmol) and thiourea (220mg, 2.86mmol) in 40 ml ethanol and 20 ml hexane

was refluxed for 2 h. Then KOH (0.32g, 5.76 mmol) in 2ml water was added for another

169

2h refluxing. After the reaction mixture was cooled down, 50ml 2N HCl was added. The


were washed with water and brine. The organic mixture was dried over anhydrous

magnesium sulfate. After filtration, the solvent was removed by rotary evaporation to

give a viscous brown solid. The product was purified by silica gel column

chromatography (eluent: n-hexane/ ethyl acetate = 4: 1) to afford a pale yellow solid

(638mg, Yield: 73%). 1H NMR (CDCl3, 500 MHZ, ppm) δ 8.25-8.24(d, 2H, J=1.25 HZ),

8.19-8.17(d, 2H, J= 7.55 HZ), 7.64-7.62 (m, 2H), 7.55-7.48 (m, 8H), 7.31-7.28 (t, 2H,

J=6.93 HZ), 4.41-4.38 (t, 4H, J = 7.58 HZ), 3.87-3.86 (d, 4H, J = 7.55 HZ), 2.00-1.94 (m,

4H), 1.84-1.81 (t, 2H, J = 7.55 HZ), 1.52-1.30 (m, 12H), 0.95-0.92 (t, 6H, J = 7.25 HZ).

13C NMR(CDCl3, 75.5MHZ, ppm) δ 141.36, 140.92, 139.76, 137.76, 131.95, 131.04,

26.92, 125.91, 122.93, 122.81, 120.98, 120.51, 118.97, 108.86, 108.48, 43.31, 31.64, 1

29.05, 27.06, 26.66, 22.59, 14.05.

5, 8, 14, 17-tetra (N-n-hexylcarbazole -3-yl) dithia[3.3]paracyclophane 20.

A solution of 1, 4-bis (N-n-hexylcarbazole-3-yl)-2,5-bis(bromomethyl) benzene(18)

(285mg, 0.37mmol) and 2,5-bis(N-n-hexylcarbazole-3-yl)-1,4-

bis(mercaptomethyl)benzene (19) (250mg, 0.37mmol) in 80 ml degassed toluene was

added dropwise with stirring to a solution of KOH (420mg, 7.5 mmol) in 300 ml ethanol

and 100 ml hexane. After the addition was completed, the reaction mixture was stirred for

48h at room temperature under the protection of nitrogen. The organic solvent was

removed under reduced pressure and 100 ml chloroform was added to dissolve the

residue. The resulting mixture was washed with water (100ml x 2) and brine. The organic

170

mixture was dried over anhydrous magnesium sulfate. After filtration, the solvent was

removed by rotary evaporation to give a pale yellow solid. The crude product was

purified by column chromatography (eluent: n-hexane/ ethyl acetate = 30:1) to afford

207mg (Yield: 44%) pale yellow solid. 1H NMR (CDCl3, 500 MHZ, ppm) δ 8.23 (s, 4H),

7.86-7.85 (d, 4H, J = 1.25 HZ), 7.60-7.34 (m, 20H), 6.79-6.76 (t, 4H, J = 7.25 HZ), 4.43-

.40 (d, 4H, J = 15.15 HZ), 4.39-4.36 (t, 8H, J = 7.25 HZ), 4.03-4.00 (d, 4H, J = 15.15

C NMR

4.38 (t, 8H, J = 7.55 HZ), 3.80-3.74 (m, 4H), 3.04-2.98 (m, 4H), 1.99-1.93 (m, 8H), 1.51-

4

HZ), 1.97-1.91 (m, 8H), 1.49-0.89 (m, 24H), 0.92-0.89 (t, 12H, J = 7.25 HZ). 13

(CDCl3, 125MHZ, ppm) δ 140.79, 140.20, 139.60, 133.54, 132.73, 132.00, 127.82,

125.59, 123.34, 123.01, 121.67, 120.56, 118.61, 108.48, 108.13, 43.33, 35.78, 31.61,

29.11, 27.10, 22.57, 14.04. MALDI-TOF: 1269.844

4, 7, 12, 15-tetra (N-n-hexylcarbazole -3-yl) [2.2]paracyclophane 21.

5, 8, 14, 17 - tetra (N-n-hexylcarbazole-3-yl)dithia[3.3] paracyclophane(20) (150mg,

0.12 mmol) was dissolved in 50ml trimethyl phosphate in 100ml conical flask. The flask

was put into a UV reactor (Hg, 180 W) and was irradiated for 24 h. The trimethyl

phosphate was removed in vacuum. The resulting mixture was added 100ml chloroform

and washed with water and brine. The organic mixture was dried over anhydrous


give a pale yellow solid. The crude product was purified by column chromatography

(eluent: n-hexane/ ethyl acetate = 30: 1) to obtain a gray solid (121 mg, Yield: 85%). 1H

NMR (CDCl3, 500 MHZ, ppm) δ 8.11-8.10 (d, 4H, J = 1.25 HZ), 7.84-7.82 (m, 4H),

7.54-7.52 (d, 4H, J = 8.2 HZ), 7.44-7.34 (m, 12H), 7.22 (s, 4H), 6.80-6.77 (m, 4H), 4.41-

171

1.29 (m, 24H), 0.91-0.88 (t, 12H, J = 7.25 HZ). 13C NMR (CDCl3, 125MHZ, ppm) δ

140.72, 140.25, 139.49, 137.13, 132.76, 132.30, 127.38, 125.52, 123.43, 123.03, 121.10,

20.36, 118.56, 108.46, 108.38, 43.30, 33.63, 31.58, 29.69, 29.09, 27.05, 22.56, 13.99.

: 1) to afford 126 mg (Yield: 40%)

ale yellow solid. 1H NMR (CDCl3, 500 MHZ, ppm) δ 8.40 (s, 2H), 7.88-7.87 (d, 2H, J =

(d, 2H, J =

1

MALDI-TOF: 1205.522

5, 8-bis (N-n-hexylcarbazole-3-yl)-14, 17-bis (9, 9-n-hexylfluorene-2-yl) dithia[3.3]

paracyclophane 22.

A solution of 2,5-bis(9,9-di-n-hexylfluoren-2-yl) -1,4-bis(mercaptomethyl)benzene(10)

(186mg, 0.22mmol) and 1,4-bis (N-hexylcarbazole-3-yl)-2,5-bis(bromomethyl) benzene

(18) (169mg, 0.22mmol) in 80 ml degassed toluene was added dropwise with stirring to

a solution of KOH (250mg, 4.5 mmol) in 300 ml ethanol and 100 ml hexane. After the

addition was completed, the reaction mixture was stirred for 48h at room temperature

under the protection of nitrogen. The organic solvent was removed under reduced

pressure and 100 ml chloroform was added to dissolve the residue. The resulting mixture

was washed with water (100ml x 2) and brine. The organic mixture was dried over


evaporation to give a yellow solid. The crude product was purified by column

chromatography (eluent: n-hexane/ ethyl acetate = 20

p

7.6 HZ), 7.76-7.71 (m, 6H), 7.53-7.09 (m, 22H), 4.46-4.37 (m, 8H), 4.13-4.10

15.75 HZ), 3.84-3.81 (d, 2H, J = 15.15 HZ), 2.02-1.99 (m, 4H), 1.58-0.69 (m, 70H). 13C

NMR(CDCl3, 125MHZ, ppm) δ 151.14, 151.06, 140.98, 140.90, 140.39, 140.00, 139.52,

133.68, 133.53, 132.55, 132.23, 131.56, 128.33, 128.03, 126.85, 126.63, 125.76, 123.87,

172

123.23, 122.98, 122.68, 121.77, 120.81, 119.65, 119.44, 118.91, 55.07, 43.33, 40.19,

39.92, 36.09, 35.33, 31.71, 31.68, 31.43, 29.74, 29.71, 29.54, 29.18, 27.13, 23.76, 23.72,

22.65, 22.62, 22.49, 14.08, 14.03. MALDI-TOF: 1436.520.

4, 7 - bis (N - n – hexylcarbazole - 3 - yl) - 12, 15-bis(9, 9 - n-hexylfluorene-2-yl) [2.2]

paracyclophane 23.

5, 8 –bis(9, 9’- di – n – hexyl– 9H- fluoren -2 – yl) – 1,4 – phenylene ) -2, 11- dithia [3,

3] paracyclophane (101mg, 0.07 mmol) was dissolved in 50ml trimethyl phosphate in

100ml conical flask. The flask was put into a UV reactor (Hg, 180 W) and was irradiated

for 24 h in room temperature. The trimethyl phosphate was removed in vacuum. The

resulting mixture was added 100ml chloroform and washed with water and brine. The

organic mixture was dried over anhydrous magnesium sulfate. After filtration, the

solvent was removed by rotary evaporation to give a yellow brown solid. The crude

duct was purified by column chromatography (eluent: n-hexane/ ethyl acetate = 20: 1)

) δ 8.17-

pro

to obtain a white solid (74 mg, Yield: 77%). 1H NMR (CDCl3, 500 MHZ, ppm

8.16 (d, 2H, J = 1.25 HZ), 7.85-7.81 (m, 4H), 7.76-7.67 (m, 4H), 7.54-7.49 (m, 6H),

7.43-7.28(m, 10H), 7.15 (s, 2H), 7.07 (s, 2H), 7.03-6.92 (m, 2H), 4.39-4.36 (t, 4H, J =

7.25 HZ), 3.80-3.70 (m, 4H), 3.03-2.94 (m, 4H), 2.00-1.93 (m, 4H), 1.73-0.56 (m, 70H).

13C NMR(CDCl3, 125MHZ, ppm) δ 151.15, 151.13, 140.98, 140.77, 140.44, 140.23,

140.04, 139.81, 139.45, 137.21, 136.95, 132.54, 132.48, 131.97, 128.65, 127.47, 126.88,

126.73, 125.59, 123.43, 123.34, 122.94, 122.79, 120.77, 120.59, 119.76, 119.65, 118.75,

108.57, 108.48, 55.04, 43.24, 40.37, 39.89, 33.69, 33.64, 31.93, 31.67, 31.56, 31.49,

173

31.21, 29.65, 29.64, 29.52, 29.36, 29.14, 27.07, 23.92, 23.78, 22.69, 22.62, 22.54, 22.33,

14.10, 14.04, 13.83. MALDI-TOF: 1373.907

1,4 –bis(thiophene-2-yl)-2,5-bis(methoxymethyl)benzene 26.

To a 150 ml one neck flask was added thiophen-2-ylboronic acid (2.77g, 21.6 mmol),

1,4-dibromo-2,5-bis(methoxymethyl)benzene (2.60g, 8.0 mmol), catalytic amount of

Bu4NBr and 60 ml toluene. Once all the monomers were dissolved, 40 ml 2 M Na2CO3

aqueous solution was added. The flask equipped with a condenser was then evacuated

and filled with nitrogen three times to remove traces of air. Pd (PPh3)4 (185 mg, 2%

mmol) was then added under a nitrogen atmosphere. The flask was again evacuated and

lled with nitrogen three times. The reaction mixture was then heated to 95 – 100 oC and

om temperature

fi

maintained for 72 h under nitrogen. The mixture was then cooled to ro

and poured into 100ml water. The resulting mixture was extracted with ether (80ml x 3)

and the combined organic extracts were washed with water and brine. The organic


removed by rotary evaporation to give a colorless liquid. The product was purified by

column chromatography (eluent: n-hexane/ ethyl acetate = 6: 1) to offer1.99 g (Yield:

76%) white solid. 1H NMR (CDCl3, 500 MHZ, ppm) δ 7.63 (s, 2H), 7.39-7.38 (m, 2H),

7.21-7.20 (m, 2H), 7.13-7.11 (m, 2H), 4.50 (s, 4H), 3.42 (s, 6H). 13C NMR(CDCl3,

125MHZ, ppm) δ 141.25, 135.26, 133.75, 131.91, 127.39, 127.26, 125.96, 72.40, 58.10.

MS (EI, m/z): 329.9(M+). HRMS-EI: 330.0751, Δ = -0.8.

1, 4-bis (thiophene-2-yl)-2, 5-bis(bromomethyl) benzene 27.

174

HBr gas was bubbled vigorously through a solution of 1, 4 –bis(thiophene-2-yl)-2,5-

bis(methoxymethyl)benzene(26) (1.50g, 4.58 mmol) in 100 ml CHCl3 for 20 minutes.

The reaction mixture was stirred for an additional 20h and neutralized with 2 M Na2CO3

aqueous solution. The organic layer was washed with water (100ml x 3) and brine. Then

was dried over anhydrous magnesium sulfate. After filtration, the solvent was removed

(CDCl3, 500 MHZ, ppm) δ 7.60 (s, 2H), 7.46-7.40 (m, 4H), 7.19-

it

by rotary evaporation to give a pale yellow solid (1.78g, Yield, 91%) without further

purification. 1H NMR

7.17 (m, 2H), 4.62 (m, 4H). 13C NMR(CDCl3, 125MHZ, ppm) δ 139.76, 136.15, 134.44,

134.05, 127.68, 127.35, 126.51, 31.34.

5, 8 - bis(thiophene - 2 - yl) - 14, 17 - bis (9, 9 – di - n – hexylfluorene - 2 - yl)

dithia[3.3]paracyclophane 28.

A solution of 2,5-bis(9,9-di-n-hexylfluorene-2-yl) -1,4-

bis(mercaptomethyl)benzene(10) (322mg, 0.38 mmol) and 1,4-bis(thiophene-2-yl)-2,5-

bis(bromomethyl) benzene(27) (165mg, 0.38 mmol) in 80 ml degassed toluene was

added dropwise with stirring to a solution of 430mg KOH (7.7 mmol) in 300 ml ethanol

and 100 ml hexane. After the addition was completed, the reaction mixture was stirred for

48h at room temperature under the protection of nitrogen. The organic solvent was

removed under reduced pressure and 100 ml chloroform was added to dissolve the

residue. The resulting mixture was washed with water (100ml x 2) and brine. The organic


removed by rotary evaporation to give a pale yellow solid. The crude product was

purified by column chromatography (eluent: n-hexane/ ethyl acetate = 30: 1) to afford

175

180 mg (Yield: 43%) pale yellow solid. 1H NMR (CDCl3, 300 MHZ, ppm) δ 7.75-6.99

(m, 24H), 4.40-4.25(m, 4H), 4.11-4.06(d, 2H, J=15HZ), 3.61-3.56(d, 2H, J=15HZ), 1.93-

1.86(m, 8H), 1.27-0.69(m, 44H). 13C NMR(CDCl3, 75MHZ, ppm), 151.08, 150.89,

42.03, 140.97, 140.57, 139.96, 139.84, 134.43, 133.00, 132.66, 131.73, 127.83, 127.72,

.77, 23.74, 22.63, 14.13, 14.05. MALDI-TOF: 1100.268.

1

126.92, 126.69, 126.35, 123.34, 122.75, 119.66, 119.45, 55.10, 40.33, 40.25, 36.13, 35.21,

31.75, 31.55, 29.86, 29

4, 7 - bis(thiophene - 2 - yl) - 12, 15 - bis(9, 9 - di - n-hexylfluorene-2-yl) [2.2]

paracyclophane 29.

5,8-bis(thiophene-2-yl)-14,17-bis (9, 9 – di - n – hexylfluorene - 2 - yl)

dithia[3.3]paracyclophane(28) (100mg, 0.09 mmol) was dissolved in 50ml trimethyl

phosphate in 100ml conical flask. The flask was put into a UV reactor (Hg, 180 W) and

was irradiated for 24 h in room temperature. The trimethyl phosphate was removed in

vacuum. The resulting mixture was added 100ml chloroform and washed with water and

brine. The organic mixture was dried over anhydrous magnesium sulfate. After filtration,

the solvent was removed by rotary evaporation to give a yellow brown solid. The crude

product was purified by column chromatography (eluent: n-hexane/ ethyl acetate = 20: 1)

to obtain a white solid (77 mg, Yield: 82%). 1H NMR (CDCl3, 500 MHZ, ppm) δ 7.75-

7.03 (m, 24H) 3.79-3.75(m, 2H), 3.57-3.52(m, 2H), 3.21-3.15(m, 2H), 2.66-2.60(m, 2H),

2.03-1.91(m, 8H), 1.29-0.60(m, 44H). 13C NMR(CDCl3, 125MHZ, ppm), δ 151.19,

150.95, 142.81, 141.25, 140.99, 139.94, 139.65, 136.96, 133.75, 132.51, 132.21, 128.50,

127.86, 126.96, 126.77, 125.71, 125.51, 123.41, 122.79, 119.65, 119.60, 55.18, 40.53,

176

40.14, 33.47, 33.44, 31.70, 31.47, 29.79, 29.70, 29.66, 23.86, 23.67, 22.56, 14.10, 14.00.

MALDI-TOF: 1038.574.

5, 8 - bis (N - n - hexylcarbazole - 3 - yl) – 14, 17 – bis (9, 9 - di - n-hexylfluorene - 2 -

20.77, 120.52, 118.58, 114.09,

8.66, 108.22, 43.21, 36.13, 35.75, 31.95, 31.62, 29.72, 29.38, 29.02, 27.04, 22.71,

yl) dithia[3.3]paracyclophane 30.

A solution of 2, 5-bis(N-n-hexylcarbazole-3-yl)-1,4-bis(mercaptomethyl)benzene(19)

(276mg, 0.41 mmol) and 1,4-bis(thiophene-2-yl)-2,5-bis(bromomethyl) benzene(27)

(177mg, 0.41 mmol) in 80 ml degassed toluene was added dropwise with stirring to a

solution of 460mg KOH (8.2 mmol) in 300 ml ethanol and 100 ml hexane. After the

addition was completed, the reaction mixture was stirred for 48h at room temperature

under the protection of nitrogen. The organic solvent was removed under reduced

pressure and 100 ml chloroform was added to dissolve the residue. The resulting was

washed with water (100ml x 2) and brine. The organic mixture was dried over anhydrous


give a pale yellow solid. The crude product was purified by column chromatography

(eluent: n-hexane/ ethyl acetate = 20: 1) to afford 165 mg (Yield: 43%) pale yellow solid.

1H NMR (CDCl3, 500 MHZ, ppm) δ 7.97-7.24(m, 24H), 4.57-4.53(d, 2H, J=21 HZ),

4.36-4.31(m, 6H), 4.17-4.14(d, 2H, J=15.0HZ), 3.73-3.70(d, 2H, J= 15.0HZ), 1.97-

1.91(m, 4H), 1.58-1.30(m, 16H), 0.95-0.92(t, 6H, J=7.5HZ), 13C NMR(CDCl3, 125MHZ,

ppm), δ 142.52, 140.74, 140.30, 139.56, 134.43, 132.87, 132.74, 132.57, 132.07, 131.75,

127.84, 127.77, 127.37, 126.42, 125.60, 123.07, 123.01, 1

10

14.14. MS (EI, m/z): 604.6(M+). MALDI-TOF: 935.05

177

4, 7 - bis (N - n - hexylcarbazole - 3 - yl) - 12, 15 - bis (9, 9 - di – n -hexylfluorene - 2 -

yl) [2.2]paracyclophane 31.

5, 8 - bis (N - n - hexylcarbazole - 3 - yl) – 14, 17 – bis (9, 9 - di - n-hexylfluorene - 2 -

yl) dithia[3.3]paracyclophane(30) (130mg, 0.14 mmol) was dissolved in 50ml trimethyl

phosphate in 100ml conical flask. The flask was put into a UV reactor (Hg, 180 W) and

was irradiated for 24 h in room temperature. The trimethyl phosphate was removed in

vacuum. The resulting mixture was added 100ml chloroform and washed with water and

brine. The organic mixture was dried over anhydrous magnesium sulfate. After filtration,

the solvent was removed by rotary evaporation to give a yellow brown solid. The crude

roduct was purified by column chromatography (eluent: n-hexane/ ethyl acetate = 20: 1)

7.98-7.97 (d, 2H, J = 7.6 HZ), 7.63-7.61 (m, 2H), 7.57-

m, 1 -7.28 2H), .16-7

p

to obtain a pale yellow solid (97 mg, Yield: 80%). 1H NMR (CDCl3, 500 MHZ, ppm) δ

8.05-8.04 (d, 2H, J = 1.25 HZ),

7.40 ( 2H), 7.30 (m, 7 .15 (d, 4H, J = 3.15 HZ), 4.37-4.34 (t, 4H, J =

7.25 HZ), 3.90-3.86 (m, 2H), 3.56-3.52 (m, 2H), 3.26-3.19 (m, 2H), 2.68-2.61 (m, 2H),

1.98-1.92 (m, 4H), 1.49-1.29 (m, 12H), 0.94-0.91 (t, 6H, J = 7.30 HZ). 13C NMR (CDCl3,

125MHZ, ppm) δ 143.35, 141.07, 140.72, 139.59, 136.95, 136.80, 133.60, 132.57,

132.37, 131.96, 127.98, 127.96, 125.59, 125.48, 125.44, 123.22, 123.09, 120.60, 120.54,

118.69, 108.75, 108.47, 43.25, 33.55, 33.52, 31.61, 29.71, 29.04, 27.03, 22.59, 14.03.

MALDI-TOF: 870.949

6.4 Molecules Synthesized in Chapter Five

2-Bromo-9,9-dihexylfluorene 1a.3

178

To a stirring solution of 2-bromofluorene (12.26g, 50.0 mmol) in DMSO(150ml) under

nitrogen, powered potassium tert-butoxide(15.16g, 135.0 mmol) was added and the

solution was cooled to room temperature. After 15 minutes, 1-bromohexane (17.6ml,

125.1mmol) in DMSO (20 ml) was added dropwise in 30 minutes. Following that, the

reaction temperature was then allowed to warm to 40 oC and the reaction mixture was

stirred overnight. Distilled water (150ml) was poured into the reaction mixture to quench

e reaction. The resulting mixture was extracted with CH2Cl2 (100ml x 3) and the

he organic mixture was dried over anhydrous magnesium sulfate.

th

combined organic extracts were washed with water (100ml x 5, to remove most of the

DMSO) and brine. T

After filtration, the solvent was removed by rotary evaporation to give a colorless liquid.

The crude product was purified by column chromatography eluting with pure hexane to

obtain 1a as colorless oil (20.2g, Yield: 98%). 1H NMR (CDCl3, 300 MHZ, ppm) δ 7.42-

7.67(m, 4H), 7.31-7.33(m, 3H), 1.90-1.95(m, 4H), 1.03-1.15(m, 12H), 0.77(t, 6H), 0.58-

0.62(m, 4H). 13C NMR(CDCl3, 75.5MHZ, ppm) δ 151.0, 150.7, 141.2, 140.3, 129.9,

127.5, 126.9, 126.1, 122.9, 121.0, 119.7, 55.2, 40.3, 31.5, 29.7, 23.7, 22.6, 14.0. MS(EI,

m/z): 414.2(M+).

2-Bromo-9, 9-dipropylfluorene 1b.3

The procedure of 1a was followed to obtain 1b from 2-bromofluorene(0.98g,

4.00mmol) as pale yellow oil (1.20g, Yield: 91%). 1H NMR (CDCl3, 300 MHZ, ppm) δ

7.54-7.77(m, 4H), 7.39-7.44(m, 3H), 2.03-2.08(m, 4H), 0.77-0.80(m, 10H). 13C

NMR(CDCl3, 75.5MHZ, ppm) δ 153.0, 150.3, 140.2, 130.0, 127.5, 127.0, 126.2, 122.9,

121.1, 121.0, 119.8, 55.6, 42.7, 17.2, 14.5. MS (EI, m/z): 328.0(M+).

179

2-Bromo-9, 9-dimethylfluorene 1c.3

The procedure of 1a was followed to obtain 1c from 2-bromofluorene(4.10g, 16.5

mol) as pale yellow oil (4.30g, Yield: 95%). 1H NMR (CDCl3, 500 MHZ, ppm) δ 7.75-

.73, 153.28, 138.28, 138.19, 130.14, 127.73, 127.23,

m

7.73(m, 1H), 7.64-7.62(m, 2H), 7.53-7.47(m, 2H), 7.40-7.39(m, 2H), 1.54(s, 6H). 13C

NMR(CDCl3, 125MHZ, ppm) δ 155

126.21, 122.70, 121.44, 121.09, 120.12, 47.15, 27.06. MS (EI, m/z): 271.7(M+).

1, 2-bis (9, 9-dimethylfluorene-2-yl)ethyne 2c.

2-Bromo-9, 9-dimethylfluorene (3.16g, 11.56mmol), Pd(PPh3)2Cl2 (0.26g, 0.72mmol)

and CuI (0.29g, 1.2mmol) were added to a 150ml round bottom flask containing 60 ml

benzene. The mixture was degassed with dry argon before adding DBU (10.8ml, 72.1

mmol) by a syringe. Following that, distilled water (0.1 ml, 4.8mmol) and ice-chilled

trimethylsilylacetylene (0.81ml, 5.73mmol) were added into the flask. The reaction

mixture was blocked from light and refluxed at 80 oC for 18 hours. The reaction mixture

was partitioned in ethyl ether and distilled water (100ml each). The organic layer was

washed with 10% HCl (3 X 80ml), saturated aqueous NaCl (100ml), dried over MgSO4,

gravity-filtered and the solvent was removed in vacuum. The crude product was purified

by column chromatography(eluent: n-hexane/ ethyl acetate = 10: 1) to obtain 3c as white

solid (1.50g, Yield: 75%). 1H NMR (CDCl3, 500 MHZ, ppm) δ 7.75-7.70(m, 4H), 7.64(s,

2H), 7.57-7.54(m, 2H), 7.45-7.44(m, 2H), 7.37-7.34(m, 4H), 1.52(s, 12H). 13C

NMR(CDCl3, 125MHZ, ppm) δ 153.91, 153.62, 139.35, 138.56, 130.65, 127.65, 127.10,

125.90, 122.66, 121.82, 120.26, 119.95, 90.33, 46.86, 27.04. MS (EI, m/z): 410.0 (M+).

180

1, 2-bis (9, 9-dihexylfluorene-2-yl)ethyne 2a.

The procedure for 2c was followed to prepare 2a from 1a( 1.00g, 2.42mmol) as white

d the resulting mixture was washed with water (100ml x 2) and

rine. The organic mixture was dried over anhydrous magnesium sulfate. After filtration,

n to give an orange yellow solid 3c(70mg,

ppm) δ 7.46-7.45(m, 7H), 1.29-7.14(m, 28H), 7.10-

6.98(m, 7H), 6.96-6.86(m, 7H), 1.05-1.00(m, 42H). 13C NMR(CDCl3, 125MHZ, ppm) δ

solid (0.50g, 66%). 1H NMR (CDCl3, 300 MHZ, ppm) δ 7.54-7.69(m, 8H), 7.32-7.34(m,

6H), 1.98(t, 8H), 1.05-1.15(m, 24H), 0.77(t, 12H), 0.58-0.66(m, 8H). 13C NMR(CDCl3,

75.5MHZ, ppm) δ 150.9, 150.7, 141.3, 140.4, 130.5, 127.4, 126.8, 125.8, 122.8, 121.5,

119.9, 119.5, 90.4, 55.1, 40.4, 31.5, 29.7, 23.6, 22.5, 13.9. MS(EI, m/z): 691.1 (M+).

1, 2-bis (9, 9-dipropylfluorene-2-yl)ethyne 2b.

The procedure for 2c was followed to prepare 2b from 1b (1.15g, 3.49mmol) as white

solid (0.63g, 82%).%). 1H NMR (CDCl3, 300 MHZ, ppm) δ 7.81-7.69(m, 8H), 7.47-

7.42(m, 6H), 2.11-2.09(m, 8H), 0.80(bs, 20H). 13C NMR(CDCl3, 75.5MHZ, ppm) δ

151.0, 150.8, 141.4, 140.5, 130.6, 127.5, 126.1, 122.9, 121.7, 120.0, 119.7, 90.6, 55.3,

42.8, 17.2, 14.5. MS (EI, m/z): 522.2 (M+).

1,2,3,4,5,6-hexakis(9,9-dimethylfluorene-2-yl)benzene 3c.

1, 2-bis (9, 9’-dimethylfluorene-2-yl)ethyne(200 mg, 0.48mmol) was dissolved in

dioxane(20ml) and the mixture was degassed for 20 minutes. After that, Co2(CO)8(30mg,

0.08 mmol) was added and the reaction mixture was refluxed for 48 hours. 100 ml

chloroform was added an

b

the solvent was removed by rotary evaporatio

35%). 1H NMR (CDCl3, 500 MHZ,

181

153.56, 152.40, 152.36, 152.32, 141.05, 140.90, 140.10, 140.06, 139.13, 135.99, 130.71,

130.62, 130.59, 130.51, 130.40, 126.71, 126.61, 126.51, 122.26, 122.21, 119.76, 119.65,

119.53, 118.50, 118.32, 46.17, 26.90, 26.76. MS (FAB, m/z): 1231.5 (M+). MALDI-TOF:

1231.425.

182

Reference

. Yu, W. L.; Pei, J.; Cao, Y.; Huang, W.; Heeger, A. J. Chem. Commun. 1999, 1837.

.; Mastrorilli, P.; Gigli, G.; Suranna, G.

1. Kim, J. E.; Song, S. Y.; Shim, H. K. Synth. Met. 2001, 121, 1665.

2. Bedard, T. C.; Moore, J. S. J. Am. Chem. Soc. 1995, 117, 10662.

3. Lee, S. H.; Tsutsui, T. Thin Solid Films 2000, 363, 76.

4. Kanibolotsky, A. L.; Berridge, R.; Skabara, P. J.; Perepichka, I. F.; Bradley, D. D.

C.; Koeberg, M. J. Am. Chem. Soc. 2004, 126, 13695.

5

6. Grisorio, R.; Piliego, C.; Fini, P.; Cosma, P

P.; Nobile, C. F. J. Phys. Chem. C. 2008, 112, 7005.

7. Paliulis, O.; Ostrauskaite, J.; Gaidelis, V.; Jankauskas, V.; Strohriegl, P.

Macromolecular Chemistry and Physics 2003, 204, 1706.

8. Rodriguez, J. G.; Tejedor, J. L.; La Parra, T.; Diaz, C. Tetrahedron 2006, 62,

3355.

9. Mills, N. S.; Burns, E. E.; Hodges, J.; Gibbs, J.; Esparza, E.; Malandra, J. L.;

Koch, J. J. Org. Chem. 1998, 63, 3017.

10. Promarak, V.; Saengsuwan, S.; Jungsuttiwong, S.; Sudyoadsuk, T.; Keawin, T.

Tetrahedron Letters 2006, 48, 89.

183

I

APPENDIX I

clei

ch as 1H, 13C, 15N, 17O and 19F have an odd number of nucleons and nuclear spin (I) of

ions. When a radio frequency is applied

requencies of the absorption peaks vs. peak

tensities constitutes a NMR spectrum.

lues, chemical shift values,

CHARACTERIZATION TECHNIQUES

Nuclear Magnetic resonance Spectroscopy (NMR)

NMR spectroscopy utilizes the magnetic properties of nuclei. In the presence of an

applied magnetic field, nuclear magnets can have an orientation in 2I+1 ways. Nu

su

½, hence they can take up one of the two orientat

to the system, this distribution is changed if the radio frequency matches the frequency at

which the nuclear magnets naturally process in the magnetic field. The radiation is

absorbed, and some nuclei in the low energy states are promoted to the higher energy

states. The absorptions are characterized by chemical shifts, which reflect the local

environment of the nuclei. A plot of the peak f

in

In 1H NMR spectroscopy, inference from the integral va

coupling constants and multiplicities provide important information about the number

and environment of different protons in the molecule. Similarly, 13C NMR spectroscopy

provides information on the kind of carbon atoms in the molecule and their environment.

Thus, NMR spectroscopy is an extremely powerful tool for studying the structure

properties of the monomers and the polymers, as well as the indication of the purity of

the products.

1H and 13C NMR spectra were recorded on Bruker DPX 300 and Bruker AMX 500 FT-

NMR spectrophotometer. Samples were analyzed in Chloroform-d or other deuterated

organic solvents. The chemical shift values were expressed relative to tetramethylsilane

as an internal standard.

Mass spectrometry (MS)

ass spectrometry involves the sorting of charged gas molecules according to their

asses. The sample is first ionized, and then allowed to be fragment and decompose. The

ons produced are accelerated by an electric field out of the ion source into a

ass-analysis sector. Mass-analysis is usually achieved in a magnetic sector. The

agnetic sector disperses the ions in curved trajectories that depend on the mass-to-

harge ratio. The mass-analyzed beam of ions is finally detected. In the commonly used

lectron-impact (EI) mode of MS, a mass spectrum is normally a plot of abundance

gainst m/z.

Mass spectrometry is useful to confirm the structure of the monomer. The mass spectra

f our monomer samples were obtained using a Micromass 7034E mass spectrometer.

igh resolution mass spectroscopy (HRMS) spectra were obtained by using either E-

CAN or peak match method.

ltraviolet-Visible Absorption Spectroscopy (UV-Vis)

UV-Vis spectrometers measure the absorption of light in the visible and “near”

ltraviolet region, i.e. in the 250-800 nm range. Ultraviolet radiation is absorbed by a

hromophore rather than the molecules as a whole. When absorption occurs, electronic

ansition of molecules takes place. It is thus particularly suitable for the study of

M

m

charged i

m

m

c

e

a

o

H

S

U

u

c

tr

II

electronic structure of conjugated pol ch contain extended π – conjugated

he Hewlett-Packard

UV-Vis-NIR spectrometer.

Photol

ur

this exc at of the absorbed radiation.

that occ

luminescence spectrometer with a xenon lamp as the light source.

Cyclic

oxidation events. It can be used to study the electrochemical behavior of species diffusing

an electrode surface, interfacial phenomena at an electrode surface and bulk properties

f materials in or on electrodes. It measures the current resulting from the (potential)

nction to polymers with a fixed scan rate expressed in mV/s. CV of the polymers were

erformed on an EG&G Parc model 273A potentiosat/galvanostat system with a three-

lectrode cell in a solution of [CH3(CH2)3]4NPF6 in dry and degassed acetonitrile at a

an rate of 100mV/s at room temperature under the protection of nitrogen. A platinum

ymers, whi

chains and exhibit unusual color changes.

T UV-Vis spectra were acquired from dilute organic solution on a

8452A diode array spectrometer or a Perkin-Elmer Lamba 900

uminescence Spectroscopy (PL)

D ing the process of absorbing ultraviolet or visible electromagnetic radiation,

molecules are elevated to an excited electronic state. Some molecules will emit part of

ess energy as light of a wavelength different from th

This process is photoluminescence, which can be considered as a deexcitation process

urs after excitation by photons.

The PL spectra of our products were measured on a Perkin-Elmer LS 50B

Voltammetry (CV)

Cyclic voltammograms is a dynamic electrochemical method for measuring reduction-

to

o

fu

p

e

sc

III

electrode (~0.08 cm2) was coated with a thin polymer film and was used as the working

electrode. A platinum wire was used as 3 electrode

was used as the

column is shorter for the larger molecules than

ifferential refractometer HPLC system using polystyrene as a standard and

the counter electrode and an Ag/AgNO

reference electrode.

Gel-Permeation Chromatography (GPC)

GPC, also known as size exclusion chromatography (SEC), is a chromatographic

method used to determine the average molecular weight distribution of a polymer

sample.1 In GPC, a packed column of inert support (a solid or gel) with a distribution of

microscopic pores is used to separate a sample into a distribution of sized molecules. The

separation is accomplished by diffusion of dissolved polymers in and out of the pores of

the packing as solvent is continuously passed through the column. The larger polymer

chains do not readily diffuse into the pores and may even be completely excluded. They

are retained less than smaller molecules, which can move freely into the pores of the

packing. The effective time spent in the

the intermediate or small sized polymer molecules. Thus the larger molecules are eluted

first followed by smaller molecules. As the name implies, SEC separates the polymer

according to size or hydrodynamic radius. This hydrodynamic radius is converted to a

molecular weight or equivalent molecular weight compared to that of a calibration

polymer (polystyrene) by means of a calibration curve.2

GPC measurement was conducted on a Waters 2690 Separation Module equipped with

a Waters 410 d

HPLC grade THF or Chloroform as eluents. The data obtained from a GPC analysis are

the weight average molecular weight (Mw), the number average molecular weight (Mn)

IV

and the polydispersity index (PI), which is the ratio of the weight- to number- average

molecular weight of a polymer.

sis (TGA)

against temperature and is particularly useful for defining the temperatures

d nitrogen flow rate of 70 cm3/min. An important piece of

ata obtained from TGA is the onset of decomposition of the polymer which relates to

requires two cells equipped with thermocouples in addition to a programmable furnace, a

Thermogravimetric Analy

TGA is an example of a thermal analysis method where the mass loss of a polymer is

recorded against linearly increasing temperature.1 The basic instrumental requirements

are simple: a precision balance, a programmable furnace and a recorder. The analysis can

be carried out in static or flowing atmosphere of an inert or active gas. TGA is widely

used in the study of thermal degradation mechanisms. In addition, the residue remaining

at high temperature gives the percent ash content of the sample. On the other hand,

differential thermogravimetric analysis (DTG) monitors the rate of change of weight with

time plotted

of initial onset of decomposition and maximum rates of decomposition.3

Thermogravimetric analysis (TGA) were conducted on a Du Pont Thermal Analyst

2100 system with a TGA 2950 thermogravimetric analyzer under a heating rate of 20

oC/min from 20 oC to 850 oC an

d

the lifetime of a PLED device.

Differential Scanning Calorimetry (DSC)

DSC involves the measurement of the difference in energy input to a sample and a

reference material while both are subjected to a controlled temperature program. DSC

V

recorder and a gas controller. The measured energy differential corresponds to the heat

content (enthalpy) or the specific heat capacity of the sample. The technique is most often

DSC was run on a Du Pont DSC 2910 module in conjunction with the Du Pont

of 20 oC/min from 20 oC to 250 oC and a

used for characterizing the Tg (glass transition temperature), Tm (the heat of fusion on

heating) and Tc (The heat of fusion on cooling).

Thermal Analyst system. A heating rate

nitrogen flow of 70 cm3/min were employed. The presence or absence of glass transition

behavior, defined as the freezing-in (upon cooling) or the unfreezing (upon heating) of

micro-Brownian chain-segmented motion involving lengths of 20-50 atoms, was

observed in the series of polymers.4

VI

VII

tographic Techniques; Noyes publication, 1996.

. Kroschwitz, J. I. Characterization of Polymers; Wiley-Interscience, 1990 Vol. 1.

sis of Polymers; Applied Science Publishers

Reference

1. Cheremisinoff, N. P. Chroma

2

3. Hay, J. N. Thermal Methods of Analy

Ltd., 1982, Chapter 6.

4. Boyer, R. F. Transitions and Relaxations; Wiley-Interscience, 1977.

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