Structures, properties, and applications of soluble polyazulene and azulene containing copolymers 1

STRUCTURES, PROPERTIES, AND APPLICATIONS OF
SOLUBLE POLYAZULENE AND AZULENE-
CONTAINING COPOLYMERS





WANG FUKE
(M Sc, Fudan Univ.)











A THESIS SUBMITTED
FOR THE DEGREE OF DOCTOR OF PHILOSOPHY
DEPARTMENT OF CHEMISTRY
NATIONAL UNIVERSITY OF SINGAPORE
2003


i

Acknowledgments

I would like to express my sincere gratitude to my supervisor, Associate Professor Lai Yee-
Hing for his invaluable guidance, constant advice through this project.

I would also like to express my appreciation to Associate Professor Kocherginsky, N and Dr
Yuri for their kind help in the EPR measurements.

In addition, I wish to express my heartful thanks to all graduate students in my research lab.
In particular, I would like to than Dr. Xu J. W., Ms. Wang W. L., Ms. Lin Y., Ms. Zhou. C.
Z., Ms. Lu H. F. Mr. Wang J. H. for their advice and friendship.

Thanks also go to Ms. Tan G. K. of the X-ray Diffraction Lab of Department of Chemistry
for her assistance in analysis of the single crystal structures, all staff of Central Instrumental
Lab, Thermal Analysis Lab, Honors Lab, and Chemical Store for their help.

I dedicate this project of work to my girl friend who has provided me with so much support
and encouragement, just when I needed them most.

Last but not least, I would like to express my gratitude to the National University of
Singapore for the award of research scholarship and for providing me with the opportunity to
carry out the research work reported in this thesis.



ii

Content
Acknowledgements ii
Content iii

Summary xi
Glossary of Symbols xix
Glossary of Abbreviations xxi
List of publications xxiii
Table of the prepared compounds and polymers xxiv
Chapter 1 introduction
1

1. Conducting polymers 1
1.1 The conductivities of conjugated polymers 2
1.2 Mechanism of Polymer Conductivity 4
1.3 Electrical Conductivity Measurement 11
2. Conjugated polymers band gap engineering 12
2.1 Band-gap of conjugated polymers 12
2.2 Reduction of band gap conjugated polymers 13
2.2.1 Minimization of bond-length alternation 14
2.2.2 Reduction of band gap by donor-acceptor systems 16
3. Advanced materials based on π-conjugated polymer 19
3.1. Chromic effect conjugated polymers 20
3.2. Conjugated polymes-inorganic hybrids 22

iii

4. Azulene and Polyazulenes 26
4.1. Unique structure and interesting properties of azulene 27
4.2 Recent application of azulene and its derivatives in materials science 29
4.3 The polyazulenes (PAZs) 31
5. Oligomers Approach 34
5.1 Monomers and Oligomers: model compound for understanding of polymer
properties 36

5.1.1 Structure/property relationships 36
5.1.2 The doping mechanism revealed from the oligomers approach 39
5.1.3 The crystal structure of oligomers 41
5.2 Monomers and Oligomers – New approach for advanced materials 43
• Molecular electronic 43
• FET 44
• Optical application 45
6. Project objective 45
7. References 47
Chapter 2 The First Aptly Characterized 1,3-polyazulene: true
polyazulene and its ethynylene derivatives for steric hindrance
release

57

Introduction 57
Results and Discussion 59
Synthesis of polyazulene 59
Synthesis of poly(azulene-ethynylene) and poly(azulene-ethynylene-thienyl) 60
Thermal Analysis 61

iv

Solubility Test 62
1
HNMR Characterization 64
FT-IR spectrum 65
Electronic Spectra 67
EPR Measurement 70
Conductivities Mesurement 74

XRD and morphology study 75
Cyclic voltammogram 77
Conclusions 78
References 80
Chapter 3 Stimuli-Responsive Conjugated Copolymers Having
Electro-Active Azulene Units in the Main Chain 81

Introduction 81
Results and Discussion 83
Monomer Synthesis and Characterization 83
Monomers characterization 84
UV-vis Spectra and EPR studies 87
Polymers synthesis and characterization 89
Gel properties study 94

v

Thermal analysis 96
UV-vis and UV-vis-NIR Spectroscopic Study 99
EPR studies 102
XRD analysis 105
Morphology of the neutral and doped copolymers 106
Electrochemical Analysis 107
Electrochemical Impedance Spectroscopy study 110
Electrical Conductivity 112
Conclusions 113
References 115
Chapter 4 Crystal Structures of Monomers and Oligomers
Containing Azulene Unit – Model Compounds for the
Corresponding Polymers

119


Introduction 119
Results and Discussion 120
Model compounds design and synthesis 120
Characterization 122
Structural Analysis 126
Structure of Monoa and Monob. 126
Structure of Oligoa and Oligob 131

vi

Structure of MonoO6 138
UV-vis Spectra and NMR studies 140
Cyclic voltammogram study 146
Conclusions 149
References 152
Chapter 5 Reason for the high conductivity of the azulene
containing copolymers by studying their monomer-TCNQ
charge-transfer crystal structures and corresponding polymers-
TCNQ charge-transfer complex
154

Introduction 154
Results and Discussion 157
Synthesis of the monomers and their charge-transfer complex 157
Characterization 159
Single-crystal structure analysis 161

Crystal structure of Monoa.TNB 161
Crystal structure of Monoc.TCNQ 166
UV-vis spectrum of the complex 172
Post-synthesis and characterization charge-transfer complex of conjugated
polymers and TCNQ 175
Electronic Spectrum and EPR study 179
Conductivity measurement of the CT complex 181
Conclusions 181
References 184

vii

Chapter 6 Coordination of Multinuclear Transitional Metal
Cluster to π-Conjugated Polymers: A New Strategy towards
Tunable Hybrids
186

Introduction 186
Results and Discussion 189
Model Compounds Synthesis and Characterization 189
Model compound synthesis 189
Structural Characterization 190
Solid-state crystal structure of model compounds 193
UV/vis spectra and MLCT effect in the model compounds 198
Synthesis of hybrids of polymer and ruthenium carbonyl cluster 200
The chromium of ruthenium carbonyl cluster coordination to the polymers
revealed by HNMR and FT-IR 202
Morphologies Studies 205
Thermal Properties 207
Optical and electronic properties studies 209

Electrical chemistry study 211
Sensitivities of the hybrids to iodine and TFA 213
Conclusions 216
References 218
Chapter 7 Novel polyradicals stabilized by the vertical and
horizontal delocalization of the electrons

220

Introduction 220

viii

Results and Discussion 223
Monomer synthesis and characterization of the cation radical 223
Polymers synthesis and characterization 227
Thermal properties 229
Electrochemical Properties 230
Electronic spectroscopy study 231
EPR spectroscopy study 234
Conclusions 236
References 237
Chapter 8 Conjugation control by changing the main backbone
conjugation type or by side aromatic substituent

239

Introduction 239
Molecular design 242
Results and discussion 243

Part 1. Conjugation control by changing the main backbone conjugation type 243
Model compounds synthesis and characterization 243
Structure analysis of the model compounds 248
Polymers synthesis and characterization 252
Optical properties 255
Part 2. Conjugation control by side aromatic substituents 257
Model compounds synthesis and characterization 257
Structural analysis 260
UV-vis spectra study 263

ix

Electrochemical properties 265
Synthesis and characterization of conjugated polymers bearing phenyl pendant
group 267
UV-vis and CV studies 270
Conclusions 272
References 275
Chapter 9 Experiment Section
277
Materials 277
Solvents 277
Chemicals 277
Instrumentation 278
Synthesis 281
Synthesis of main compounds monomers 281
Synthesis of polymers 311
Chapter 10 Conclusions and Suggestions for future work

320

Conclusions 320
Suggestions 323
Appendix 324


x

Summary

A series of azulene-based conjugated polymers and their model compounds have been
synthesized and their interesting properties reported. These novel materials feature many
interesting properties, such as the chromic effect upon protonation, high conductivity
upon doping, formation of the charge-transfer complex with electron-acceptor,
coordination with transitional metal complex, and the formation of stable polyradicals.
These advanced materials offer technologically useful applications in, for example,
electrochromic devices, molecular electronics, catalysis, and anti-oxidants. Furthermore,
to gain insight into the relationship between the structure and properties of these
conjugated polymers, corresponding model compounds were synthesized and their single
crystals were prepared. Results reveal that these are ideal model compounds for
investigating the structure-properties relationship, doping mechanism, and the
coordination mode of the formation of hybrids.
The focus of this work has been to develop novel materials by inserting the intact azulene
into the polymer backbone. This is attractive because of the special optical and electrical
properties of azulene. As a non-alternated 10-π electron aromatic system with
pronounced polarizability and a tendency to form stabilized radical cations as well as
anions, azulene should be predestinated to be a building block for the construction of
new materials with interesting chemical and physical properties. However, up to now,
only polyazulene has been prepared without detailed characterization because of its
insolubility. The reported HNMR spectrum for polyazulene indicates destruction of the

unique structure of azulene. Thus, in Chapter 2, we show the preparation of a truly

xi

soluble 1,3-polyazulene by dehalogenative polycondensation of 1,3-dibromoazulene,
using an organonickel catalyst. Furthermore, 1,3-polyazulene was characterized by
1
HNMR spectroscopy, IR, and elemental analysis, which shows that azulene still kept its
unique structure in the polymer backbone. Most interestingly, the polymer exhibits high
conductivity and paramagnetic properties upon protonation.
To increase the process-ability of azulene-containing polymers and to develop novel
materials, copolymers containing azulene moiety and 3-aklyl-thiohene were prepared and
investigated (Chapter 3). The resulting copolymers showed high thermal stability in air
and good solubility in most organic solvents. Interestingly, chromic effect upon
protonation and reversible protonation-deprotonation (P-DP) processes was observed via
UV-vis and UV-vis-NIR spectroscopy in solution and at solid state. This indicates the
potential application of these copolymers in sensors. Moreover, the sensitivity of these
copolymers to the external stimuli was also investigated in detail by EPR experiments
and conductivities measurements. Especially within the EPR experiments, nitrogen-
oxygen permeation tests showed the radical content decreased in the presence of O
2
, and
recovered when vented with N
2
, indicating that these copolymers can be used as anti-
oxidants. These copolymers can be rendered conducting (1-100 S/cm) through two
independent routes: doping with iodine or protonation with trifluoroacetic acid (TFA).
The SEM studies on morphology revealed the formation of nano-scale doping centres in
the iodine doped sample and formation of conductive channel in the TFA protonated
sample, which may be have contributed to the high conductivity of the copolymers.

Doping and protonation mechanisms were further investigated by cyclic voltammetry
(CV), EPR, and electrochemical impedance spectroscopy (EIS). The stable doping state

xii

and mechanism differences between TFA protonation and iodine doping were observed
during these experiments.
To better understand the relationship between the structure and properties of these
copolymers, five model compounds were synthesized by Grignard coupling or Stille
coupling, and their crystals were prepared. These compounds were characterized by
NMR, FT-IR and 2-D NMR techniques. Their single crystal structures showed that a
large torsion angle existed between the azulene ring and the thiophene ring in these
model compounds. In general, this explains the amorphous structure of the resulting
copolymers and the identification of the UV-vis spectra of these copolymers in solution
and at solid state. The investigation of the UV-vis spectra, EPR and
1
HNMR of the
protonated model compounds revealed the formation of the azulenium cations during
protonation. Cyclic voltammetry experiments revealed cation formation in the monomers
and dication formation in these oligomers.
Yet, a question arises when comparing the results in Chapter 3 and Chapter 4. In Chapter
3, our copolymers showed high conductivity upon doping, often observed in the coplanar
conjugated polymers, while we found a large torsion angle (> 35
0
) between the azulene
ring and the thiophene ring in these model compounds (Chapter 4). Thus, we must
answer why these conjugated polymers with large torsion angle show high conductivity.
To answer this question, a series of charge transfer (CT) model compounds that mimic
the doping process were synthesized and their single crystals were prepared (Chapter 5).
An important feature of these charge-transfer crystals is the rotation of one thiophene ring

before and after “doping”. Single crystal analysis of these CT complex structures showed
that after formation of the CT complex, one thiophene ring rotated to the plane of the
azulene ring. That is, one torsion angle between the azulene ring and thiophene ring

xiii

greatly decreased (<10
0
). Also, the UV-vis spectra experiments showed the charge
transfer between the monomers and electron-acceptors, such as TCNQ and TNB. Based
on these observation, a novel charge-transfer complex between the conjugated polymers
and electron-acceptors, such as TCNQ, were prepared. These CT polymers were
characterized and confirmed by HNMR, FT-IR, UV-vis spectra and EPR. HNMR spectra
and thermal analysis confirm the formation of the CT complex and calculated the ratio
between TCNQ and conjugated donor polymers. The UV-vis spectra and EPR
experiment confirmed the charge-transfer interaction between TCNQ and the π-
conjugated polymers.
To further develop the CT complex, based on the conjugated polymers, we carried out
design and synthesis of a metal-ligands charge-transfer (MLCT) complex between these
copolymers and ruthenium carbonyl cluster. Novel organometallic conjugated polymers
with multinuclear ruthenium clusters were prepared (Chapter 6) by means of refluxing
the conjugated polymers with Ru
3
(CO)
12
in xylene. The chromium, within the ruthenium
carbonyl cluster coordination on the azulene, controls the electronic and optical
properties of the resulting hybrids, as revealed by HNMR spectrum, UV-vis spectrum
analysis and CV studies. This post coordination process offers a flexible and
straightforward route to organometallic polymers that have any desired composition, and

thus, tunable optical and electronic properties. Furthermore, this is also the first example
of transitional metal cluster attachment onto a conjugated polymers support. The
morphologies, found with SEM, reveal an increase in surface area of the resulting hybrids
via formation a sphere structure, greatly increasing the catalyst contact area. Quartz
crystal microbalance (QCM) measurements also displayed the difference in sensitivity of
our hybrids to iodine vapour from that of metal free polymers. To better understand the

xiv

properties of the resulting organometallic conjugated polymers and the coordination
mode of these ruthenium carbonyl cluster to the conjugated polymers, six model
compounds were prepared. Two of our model compounds were obtained as single crystal
and their crystal structures data showed that coordination were occurred between the
azulene ring and the ruthenium cluster; three or four multi-metal cluster were formed in
these hybrid system.
Inspired by the stability of the azulenium cation radicals observed (Chapter 3) when we
studied the EPR behaviour of those copolymers, we designed a more stable polyradical
system by stabilizing the polyradical with a horizontal and vertical directionality. In
Chapter 7, we give our design of a conjugated polymer system containing azulene and
benzene in the polymer backbone via 1,3-conjugation of azulene. In this system, upon
potonation or doping, radicals will align into the five-membered ring of azulene, which
will be stabilized by the following two approaches: the un-paired electrons of the radicals
is delocalized to the tropolynium cation of the azulene’s seven-membered ring in the
vertical direction and to the conjugated polymer backbone in the horizontal direction. The
polymers were synthesized by the Suzuki coupling reaction and characterized by NMR
and FT-IR. The polymers showed high thermal stability and oxidation potentials. Upon
doping with iodine or protonation with TFA, both polymers could be converted into the
expected stable polyradicals, as confirmed by UV-vis spectrum, FT-IR spectrum analysis
and EPR measurements. UV-vis spectra revealed the high stability of polyradicals in
solution. Polymers solution protonated with 10% TFA in chloroform were left in

atmosphere for 2 days, only the intensity increase of the longest absorption was found.
Further stability tests of the polyradicals system at solid state were carried out using EPR
measurements. The EPR intensity of the obtained polyradicals system showed no

xv

significant change, even after atmospheric storage for approximately 2 months. The high
stability of the resulting polyradicals make it suitable to be applied as anti-oxidant,
biological indictors.
Finally, factor that influence the conjugation of the resulting materials, that is control of
the band gap of the resulting materials, was investigated (Chapter 8) from two points of
view: the main backbone electronic geometry, and the side conjugation. In the first
approach, we greatly lowered the band gap of the resulting materials by changing the 1,3-
coupling to the 2,6-coupling azulene in the main backbone. The latter is the more
favourable of quinoid structure and can be looked at as an intra-molecule donor-acceptor
system. Two 2,6-coupling polymers were prepared and the electronic absorption showed
that these polymers red-shifted approximately 100 nm, when compared with that of the
corresponding 1,3-coupling conjugated polymers. Furthermore, we found that that these
2,6-coupling conjugated polymers do not protonate with TFA, which confirms our former
conclusion that the protonation of these 1,3-azulene-coupling polymers mainly occurred
at the five-membered ring of azulene; The quinoid structure of these 2,6-coupling
materials was confirmed by the single crystal data analysis of their model compounds. In
the second approach, three model compounds, bearing side-phenyl rings at different
positions, were synthesized and investigated. Compared with their corresponding
polymers, we concluded that the conjugation effect of the side-phenyl ring plays a more
signficant role than their steric effect.
In conclusion, several novel materials containing azulene have been successfully
prepared, and their interesting properties and potential applications were investigated in
detail. To better understand these interesting materials properties and to gain insight into
the mechanism of doping or protonation, model compounds and their single crystals were

xvi

prepared and studied. Their structures and properties revealed that they are ideal model
compounds for the corresponding materials, and in fact, these model compounds
themselves exhibit characteristic of advanced materials.
All research and the relationship between different chapters can be illustrated clearly in
the following chart:







xvii
xviii



(2) only
PAz was
reported
but it was
insoluble
with non-
defined
structure
To increase the
processability

To develop
advanced
materials
Copoly(azulene-3-alkylthiophene) prepared with
the following interesting properties (Ch.3):
(1) high thermal and electrical stability
(2) chromic effect upon protonation
(3) reversible protonation-deprotonation
process and doping-dedoping process
(4) high stability of cation radical
(5) high conductivity
(6) nano-scale doping centre formation
(7) high gel swelling ratio
(8) similar properties to polyaniline
Stable polyradical system designed based on the
vertical and horizontal delocalisation of unpaired
electrons, with potentials application as anti-
oxidants, sensors, and detector
(Ch.7)
Properties of “doped-state” polymers correlated to
CT model compounds and resulting CT polymers
(Ch.5)
MLCT model
compounds and
polymers prepared with
potential application in
sensor and catalysis
(Ch.6)
Properties of neutral-
state polymers

correlated to model
compounds and their
single crystal analysis
(Ch.4)
Association of
conjugation effect to
properties of main
polymer backbone and
the aryl side chain
(Ch.8)
The first successful synthesis
soluble 1,3-polyazulene with
high conductivity (Ch. 2)
Unique properties of azulene
make it a good candidate as
building block for advanced
materials
(1)
azulene
was
scarcely
used as
building
block for
materials

Glossary of Symbols


R alkyl

OR alkoxy

chemical shift
M
w
weight average molecular weight
M
n
number average molecular weight
ρ
specific resistivity

charge carrier mobility

conductivity
S/cm Seimens per centimeter
λ
max

absorption peak wavelength
d
film thickness
eV electron volt
E
g
bandgap
E
pa
anodic peak potential
E

pc
cathodic peak potential
T
g
glass transition temperature
T
d
degradation temperature
M mol/L
n
number of charge carriers
n
number of electrons

xix

R
total resistance (R
i
+ R
e
)
R
e
electronic resistance
R
i
ionic resistance
R
low

low frequency resistance
Z
impedance
Z'
real impedance
Z''
imaginary impedance
h Plank’s constant
ρ
v
volume/intrinsic resistivity
ρ
s

surface resistivity

xx

Glossary of Abbreviations

Bu butyl
CV cyclic voltammetry/voltammogram
dppp bis(diphenylphosphino)phenylene
DMF N,N-dimethyl formamide
Et ethyl
ECL effective conjugation length
FTIR fourier transform infrared
HOMO highest occupied molecular orbital
HH head-to-head
HT head-to-tail
HH head-to-head
TT tail-to-tail
GPC gel permeation chromatography
PDI polydispersity index
UV-vis ultra-violet and visible spectroscopy
IR infrared
ITO indium tin oxide
LUMO lowest unoccupied molecular orbital
Me methyl
MLCT metal-to-ligand charge transfer
MS mass spectrum

xxi

NIR near infrared
DSC differential scanning calorimetry
TGA thermogravimetric analysis
DTG derivative thermogravimetry
XRD X-ray diffraction
TFA trifluoroacetic acid
XPS x-ray photoelectron spectroscopy
TCNQ tetracyano-p-quinodimethane
TNB 1,3,5-trinitrobenzne
TTF tetrathiafulvalene
CT charge-transfer
EIS electrochemical impedance spectroscopy
QCM quartz crystal microbalance
EPR electron paramagnetic resonance












xxii

List of publications

[1] Wang F, Lai Y-H, “Enhanced electrical and optical of polymers incorporating
Non-benzenoid hydrocarbons,” Singapore International Chemical Conference II,
2001, 10.
[2] Wang F, Lai Y-H, “Novel band-gap controlled polymers,” Singapore International
Chemical Conference II, 2001, 10.
[3] Wang F, Lai Y-H, “Novel highly conductive copolymers with dipolar non-benzoid
aromatic units in the main chain,” Macromolecules, 2003, 36, 536.
[4] Wang F, Lai Y-H, Kocherginsky, N. M., Kosteski, Yu. Yu. The First Fully
Characterized 1,3-Polyazulene: High Electrical Conductivity Resulting from Cation
Radicals and Polycations Generated upon Protonation,” Organic Lett. 2003, 5, 995.
[5] Wang F, Lai Y-H,
Han MY, “Post-Coordination of Multinuclear Transitional Metal
Clusters to Azulene-Based Polymers: A Novel Strategy for Tuning Properties in π-
Conjugated Polymers,” Organic Lett. 2003, 5, 4791.
[6] Wang F, Lai Y-H, Han, M-Y, “Stimuli-Responsicve Conjugated Copolymers
Having Electro-Active Azulene and Bithiophene Units in the Polymer Skeleton: Effect
of Protonation and p-Doping on Conducting Properties,” Macromolecules, 2004,
Accepted.



xxiii
xxiv
Table. Polymers and main compounds prepared in this thesis.


Chapter
No.
Main compounds in each chapter Polymers or Oligomers

n

Polyazulene

n

Poly(azulenyl-ethynylene)






Chapt.2

TMS
TMS


1,3-Bis-trimethylsilanylethynyl-
azulene



1,3-DIethynyl-azulene


S
n

Poly(azulenyl-ethynylene-thenyl)


xxv
S
RR
n
S

a, R = H
b, R = Me
c, R = OMe
d, R = C
4
H
9

e, R = C
7
H
15

f, R = C
10
H
21

g, R = C
14
H

29






Chapt.3
S
Br
R


1-Bromo-3-(3-alkyl-2-thienyl)
azulene (BrTAa-g)

SS
RR


1,3-Bis(3-alkyl-2-thienyl) azulene
(Monoa-g)


Polya-g

Chapt.4

S
Me
Bu
3
Sn


2-(4-methyl-5-phenyl-thenyl)-
tributylstannane





S
S
O
O


MonoO6

SS


Oligoa