Soluble and stable near infrared dyes based on polycyclic aromatic compounds

Soluble and Stable Near-Infrared Dyes Based
on Polycyclic Aromatic Compounds





Jiao Chongjun
M.Sc., Soochow University




A THESIS SUBMITTED
FOR THE DEGREE OF PHILOSOPHY
DEPARTMENT OF CHEMISTRY
NATIONAL UNIVERSITY OF SINGAPORE
2011


ACKNOWLEDGEMENTS
This PhD thesis marks the end of a long journey and I would like to take this
opportunity to thank all those persons who have given their invaluable assistance
for making this journey possible.
First of all I would like to express my heartfelt gratitude and sincere thanks to
my supervisor Dr. Wu Jishan for all his scientific guidance, invaluable
suggestions and timely encouragement over the past few years. Without these my

PhD thesis would not have been possible. I am fortunate to have such an
outstanding supervisor, whose enthusiasm towards scientific research and creative
ideas will be kept in my mind throughout my life.
Second of all I would like to thank Dr. Chi Chunyan as well as all the
members of Wu and Chi’s group, both past and present, for sharing their
knowledge and for their support during group meetings and seminar discussions. I
had a pleasant and unforgettable time working with them in the lab for the last
four years.
Particular thanks should be given to our collaborators: Dr. Huang Kuo-wei
who conducted TD-DFT calculations, Prof. Wang Peng who constructed and
characterized DSC devices, and Prof. Xu Qinghua who measured fluorescence
lifetimes of my perylene-fused porphyrin NIR dyes.
I am also grateful to the staff in the department of chemistry for their kind
assistance during my PhD career. My warmest thanks also go to National
University of Singapore (NUS) and Singapore government for providing me with


financial support.
Last but certainly not least, I am profoundly indebted to my parents, Mr. Jiao
Erzheng and Mrs. Tan Zhenyi, and my wife Ms. Wang Li who always strongly
support me, love me and take pride in me. They always stood right next to me
during the troubles and toughness at various stages of my PhD work.


i
Thesis Declaration

The work in this thesis is the original work of Jiao Chongjun, performed
independently under supervision of Dr. Wu Jishan, (in the laboratory Organic
Electronics & Supramolecular Chemistry), Chemistry Department, National

University of Singapore, between 2007 and 2011.

The content of the thesis has been partly published in:

(1) C. Jiao, J. Wu*, “Fused polycyclic aromatic compounds with near infrared
absorption and emmision”, Synlett. 2012, 23, 171-184.
(2) C. Jiao, N. Zu, K. Huang, P. Wang*, J. Wu*, “Perylene anhydride fused
porphyrins as near-infrared sensitizer for dye-sensitised solar cells”, Org. Lett.
2011, 13, 3652-3655.
(3) C. Jiao, L. Zhu, J. Wu*, “BODIPY-fused porphyrins as soluble and stable
near-IR dyes”, Chem. Eur. J. 2011, 17, 6610-6614 (Highlighted by T. M.
Swager et al., Synfacts, 2011, 8, 0851).
(4) C. Jiao, K. Huang, J. Wu*, “Perylene-fused BODIPY dye with near-IR
absorption/emission and high photostability”, Org. Lett. 2011, 13, 632-635.
(5) C. Jiao, K. Huang, C. Chi, J. Wu*, “Doubly and triply fused
porphyrinperylene monoimides with large dipole moment and high photostability”,
J. Org. Chem. 2011, 76, 661-664 (Highlighted by T. M. Swager et al., Synfacts,


ii
2011, 4, 0379).
(6) C. Jiao, J. Wu*, “Nanosized graphenes: chemical synthesis and applications
in materials science”, invited book chapter in the book “Graphene: synthesis
and applications”, Taylor and Francis Books / CRC Press, 2011, p145-182.
(7) C. Jiao, K. Huang, Z. Guan, Q. Xu, C. Chi, J. Wu*, “N-annulated
perylene-fused porphyrins with enhanced NIR absorption and emission”, Org.
Lett. 2010, 12, 4046-4049.
(8) C. Jiao, J. Wu*, “New soluble and stable NIR dyes based on polycyclic
aromatics”, Curr. Org. Chem. 2010, 14, 2145-2168.
(9) C. Jiao, K. Huang, K. Zhang, J. Luo, C. Chi, J. Wu*, “Bis-N-annulated

quaterrylenebis(dicarboximide)s as a new soluble and stable NIR dye”, Org. Lett.
2009, 11, 4508-4511 (Highlighted by T. M. Swager et al., Synfacts, 2010, 1,
0044).
(10) L. Zhu,
†
C. Jiao,
†
D. Xia, J. Wu*, “N-annulated perylene dyes with
adjustable photophysical properties”, Tetrahedron Lett. (
†
equal contribution)
2011, 52, 6411-6414.


_____________ ______________ _______________
Name Signature Date


iii
TABLE OF CONTENTS

Thesis declaration

i
Table of contents

iii
Summary

vii

List of abbreviations

ix
List of publications

xi
List of figures

xiv
List of schemes

xvii
List of tables

xviii
Chapter 1 Introduction
1
1.1 Introduction 1
1.2 Literature review 3
1.2.1 Rylene derivatives 3
1.2.2 Porphyrin-based molecules 13
1.2.3
Phthalocyanine derivatives
19
1.2.4 Summary and outlook 22
1.3 Objectives 22
1.4 References 24
Chapter 2 “Push-pull” N-annulated perylene dyes with
adjustable photophysical properties
30

2.1 Introduction 30
2.2 Results and discussion 32
2.3 Conclusion 40
2.4 Experimental section 40
2.4.1 General 40
2.4.2 Detailed synthetic procedures and characterization data 42
2.5 References 50
Chapter 3 Bis-N-annulated quaterrylenebis(dicarboximide)s as
52


iv

soluble and stable NIR dyes
3.1 Introduction 52
3.2 Results and discussion 54
3.3 Conclusion 63
3.4 Experimental section 63
3.4.1 General 63
3.4.2 Detailed synthetic procedures and characterization data 64
3.5 References 73
Chapter 4 Perylene-fused Porphyrins as NIR dyes with tunable
absorption/emission
77
4.1 N-annulated perylene-fused porphyrins with enhanced
near-IR absorption and emission
77
4.1.1 Introduction 77
4.1.2 Results and discussion 79
4.1.3 Conclusion 88

4.1.4 Experimental section 88
4.1.4.1 General 88
4.1.4.2 Detailed synthetic procedures and characterization data 90
4.1.4.3
Transient absorption and pump probe experiments
102
4.2 Doubly and triply fused porphyrin-perylene monoimides
with large dipole moment and high photostability
104
4.2.1 Introduction 104
4.2.2 Results and discussion 106
4.2.3 Conclusion 113
4.2.4 Experimental section 114
4.2.4.1 General 114
4.2.4.2 Detailed synthetic procedures and characterization data 115
4.3 References 119
Chapter 5 Perylene and porphyrin-fused BODIPYs as soluble
124


v
and stable NIR dyes
5.1 Perylene-fused BODIPY dyes with near-IR absorption,
emission and high photostability
124
5.1.1 Introduction 124
5.1.2 Results and discussion 125
5.1.3 Conclusion 135
5.1.4 Experimental section 135
5.1.4.1 General 135

5.1.4.2 Detailed synthetic procedures and characterization data 136
5.2
BODIPY-fused porphyrins as soluble and stable near-IR
dyes
147
5.2.1 Introduction 147
5.2.2 Results and discussion 149
5.2.3 Conclusion 157
5.2.4 Experimental section 158
5.2.4.1 General 158
5.2.4.2 Detailed synthetic procedures and characterization data 159
5.3 References 165
Chapter 6 Perylene anhydride-fused porphyrins as NIR
sensitizers for dye-sensitized solar cells
170
6.1 Introduction 170
6.2 Results and discussion 172
6.3 Conclusion 179
6.4 Experimental section 180
6.4.1 General 180
6.4.2 Detailed synthetic procedures and characterization data 181
6.4.3 Device fabrication and characterization 190
6.5 References 192
Chapter 7 Conclusions and future research
196
7.1 Summary of results 196


vi

7.2 Future research 199
Appendix NMR spectra of all new compounds and MALDI-TOF
spectra of target molecules
201


vii

SUMMARY
Current developments in the field of electronics and in the area of bioimaging
have boosted interest in the development of next-generation functional dyes. A
recent rising interest is the design and synthesis of so-called near infrared (NIR)
dyes which are required for various advanced technologies. Many commercially
available NIR dyes such as cyanine and polyene dyes suffer from inherent
drawbacks due to their insufficient photostability. Additionally, some NIR
dyes/pigments also suffer from poor solubility for practical applications. Thus, the
purpose of this thesis was to design and synthesize soluble and stable NIR dyes.
In this dissertation, polycyclic aromatic compounds (perylene, porphyrin and
BODIPY units) have been utilized and two strategies (“push-pull”, core extension)
have been adopted to synthesize numerous π-extended molecules with varied
physical and optical properties. All the new compounds synthesized in this thesis
were structurally verified by different spectroscopic methods. Throughout the
research work, solubility and stability problems have been resolved for theses
highly conjugated systems after state-of-art design and modifications. The
fundamental structure-property relationships were systematically investigated and
experimental experiences were accumulated. Furthermore, preliminary
examination of applications of our NIR dyes was conducted, which may pave the
way for a broad range of applications in future.
Therefore, it is inevitable that more and more soluble and stable NIR dyes
based on polycyclic aromatic compounds will be synthesized in our group in the

viii
future and these newly developed compounds will play important roles in
materials science, including solar cells, bio-imaging, sensor, and so on.

Key Words: NIR dyes, perylene, porphyrin, BODIPY, solar cells




ix

LIST OF ABBREVIATIONS

BAHA tris(4-bromophenyl) aminium hexachloroantimonate
BOC tertiary butoxycarbonyl
BODIPY 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene
t-Bu tertiary butyl
COD cis, cis-1,5-cyclooctadiene
CV cyclic voltammetry
DCM dichloromethane
DDQ 2,3-dichloro-5,6-dicyano-1,4-benzoquinone
DMF N, N-dimethylformaldehyde
DPV differential pulse voltammetry
DSC dye-sensitized solar cell
EA ethyl acetate
EI electron ionization
FF fill factor
HBC hexa-peri-hexabenzocoronene

HOMO highest occupied molecular orbital
HPLC high performance liquid chromatography
IPCE photon-to-current conversion efficiency
J
sc
short circuit current density
LUMO lowest unoccupied molecular orbital
MALDI-TOF matrix-assisted laser desorption/ionization-time-of-flight
NBS N-bromosuccinimide
NIR near-infrared
NLO nonlinear optical
NMR nuclear magnetic resonce
NP N-annulated perylene
NPDI N-annulated perylene dicarboxylic imide


x
PAH polycyclic aromatic hydrocarbon
PC phthalocyanine
PDI perylene tetracarboxylic diimide
PL photoluminescence
QY quantum yield
TD-DFT time-dependent density function theory
T
f
trifluoromethanesulfonyl
TFA
trifluoro acetic acid
THF tetrahydrofuran
TLC thin layer chromotography

TMS tetramethylsilane
TPA two photon absorption
TsOH·H
2
O p-toluene sulfonic acid monohydrate
UV ultraviolet
Vis visable
V
oc
open circuit voltage


xi

LIST OF PUBLICATIONS AND CONFERENCES
Publications during PhD studies
(1) C. Jiao, J. Wu*, “Fused polycyclic aromatic compounds with near infrared
absorption and emmision”, Synlett. 2012, 23, 171-184 (invited account).
(2) C. Jiao, N. Zu, K. Huang, P. Wang*, J. Wu*, “Perylene anhydride fused
porphyrins as near-infrared sensitizer for dye-sensitised solar cells”, Org. Lett.
2011, 13, 3652-3655.
(3) C. Jiao, L. Zhu, J. Wu*, “BODIPY-fused porphyrins as soluble and stable
near-IR dyes”, Chem. Eur. J. 2011, 17, 6610-6614 (Highlighted by T. M.
Swager et al., Synfacts, 2011, 8, 0851).
(4) C. Jiao, K. Huang, J. Wu*, “Perylene-fused BODIPY dye with near-IR
absorption/emission and high photostability”, Org. Lett. 2011, 13, 632-635.
(5) C. Jiao, K. Huang, C. Chi, J. Wu*, “Doubly and triply fused
porphyrinperylene monoimides with large dipole moment and high photostability”,
J. Org. Chem. 2011, 76, 661-664 (Highlighted by T. M. Swager et al., Synfacts,
2011, 4, 0379).

(6) C. Jiao, J. Wu*, “Nanosized graphenes: chemical synthesis and applications
in materials science”, invited book chapter in the book “Graphene: synthesis
and applications”, Taylor and Francis Books / CRC Press, 2011, p145-182.
(7) C. Jiao, K. Huang, Z. Guan, Q. Xu, C. Chi, J. Wu*, “N-annulated
perylene-fused porphyrins with enhanced NIR absorption and emission”, Org.
Lett. 2010, 12, 4046-4049.


xii

(8) C. Jiao, J. Wu*, “New soluble and stable NIR dyes based on polycyclic
aromatics”, Curr. Org. Chem. 2010, 14, 2145-2168.
(9) C. Jiao, K. Huang, K. Zhang, J. Luo, C. Chi, J. Wu*, “Bis-N-annulated
quaterrylenebis(dicarboximide)s as a new soluble and stable NIR dye”, Org. Lett.
2009, 11, 4508‐4511 (Highlighted by T. M. Swager et al., Synfacts, 2010, 1,
0044).
(10) L. Zhu,
†
C. Jiao,
†
D. Xia, J. Wu*, “N-annulated perylene dyes with
adjustable photophysical properties”, Tetrahedron Lett. (
†
equal contribution).
2011, 52, 6411-6414.
(11) J. Li, C. Jiao, K. Huang, J. Wu*, “Lateral Extension of π-Conjugation along
the Bay Regions of Bisanthene via Diels-Alder Cycloaddition Reaction”, Chem.
Eur. J. 2011, 17, 14672-14680.
(12) L. Zeng, C. Jiao, X. Huang, K. Huang, W S., Chin, J. Wu*,
“Anthracene-Fused BODIPYs as Near-Infrared Dyes with High Photostability”,

Org. Lett. 2011, 13, 6026-6029.
(12) J. Yin, K. Zhang, C. Jiao, J. Li, C. Chi, J. Wu*, “Synthesis of functionalized
tetracene dicarboxylic imides”, Tetrahedron Lett. 2010, 51, 6313-6315.
(13) J. Shao, Z. Guan, Y. Yan, C. Jiao, Q. Xu, C. Chi*, “Synthesis and
characterizations of star-shaped octupolar triazatruxenes-based two-photon
absorption chromophores”, J. Org. Chem. 2011, 76, 780–790.

Conferences


xiii
(1) “Novel near-infrared dyes based on ‘p’ chemistry”, 27 June 2011, International
Conference on Materials for Advanced Technologies, Singapore (Oral
presentation).
(2) “Novel NIR dyes based on P chemistry”, 15 October 2010, The Second

Asian
NIR Symposium, China (Oral presentation).
(3) “New soluble and stable near infrared dyes”, 05 March 2010, NUS-NSU
bilateral symposium, Singapore (Poster presentation).
(4) “Bis-N-annulated quaterrylenebis(dicarboximide)s as a new soluble and stable
NIR dye”, 08 December 2009, 5
th
Mathematics and Physical Sciences Graduate
Congress, Thailand (Oral presentation).
(5) “Bis-N-fused quaterrylenebis(dicarboximide): A novel stable and soluble NIR
dye”, 17 December 2009, Singapore International Conference of Chemistry-6,
Singapore (Poster presentation).

xiv
LIST OF FIGURES

Figure 1.1
A general structure of rylene molecules 3
Figure 1.2
Structure of rylene bis(dicarboximide)s 6
Figure 1.3
Meso-substituted bisanthenes 9
Figure 1.4
Structures of “push-pull” perylene diiimides 10
Figure 1.5
Structure of quinoidal bisanthene 12
Figure 1.6
Structure and nomenclature of porphyrin 14
Figure 1.7
Doubly linked porphyrin tapes 16
Figure 1.8
Structures of triply linked porphyrin tapes 18
Figure 1.9
Structures of arene-fused porphyrins 19
Figure 1.10
Structures of phthalocyanine (Pc) derivatives 21
Figure 2.1
Structures of “push-pull” dyes 31
Figure 2.2
(a) Normalized UV-vis absorption spectra of NP based dyes in
DCM (1.0 x 10

-5
M). (b) Normalized emission spectra of NP
based dyes in DCM (1.0 x 10
-6
M). (c) Normalized UV-vis
absorption spectra of NP based dyes 2-1 to 2-4 in thin film. (d)
Normalized emission spectra of NP based dyes 2-1 to 2-4 in thin
film
36
Figure 2.3
Cyclic voltammograms of compounds 2-1 to 2-4 in DCM
39
Figure 3.1
Molecular structures of bis-N-annulated quarterrylene 3-2 and
quarterrylenebis(dicarboximide) 3-1
53
Figure 3.2
Normalized UV-vis-NIR absorption spectra (3 x 10
-6
M) and
photoluminescence spectra (4 x 10
-7
M) of compounds 3-1 and
3-2 in chloroform.
57
Figure 3.3
The optimized geometric structures of 3-1-Me and 3-2-Me
59
Figure 3.4
Cyclic voltammograms of compounds 3-1 and 3-2 in

dichloromethane
61
Figure 4.1
Structures of NP-fused porphyrins 78


xv
Figure 4.2
UV-vis-NIR absorption spectra of 4-1, 4-2, 4-5, and 4-8 in
toluene (1.0 × 10
-5
M).
83
Figure 4.3
Normalized photoluminescence (excitation wavelength = 700
nm and 920 nm, respectively) spectra of compounds 4-1 and 4-2
84
Figure 4.4
Optimized structures and frontier molecular orbital profiles of
compounds 4-1 and 4-2
85
Figure 4.5
Cyclic voltammograms of compounds 4-1 and 4-2 in
dichloromethane
86
Figure 4.6
Structures of perylene-fused porphyrins 104
Figure 4.7
UV-vis-NIR absorption spectra of 4-14 and 4-15 in toluene (1.0
x 10

-5
M)
108
Figure 4.8
Optimized structures and frontier molecular orbital profiles of
compounds 4-14 and 4-15
109
Figure 4.9
Cyclic voltammograms of compounds 4-14 and 4-15 in DCM
110
Figure 4.10
UV-vis-NIR absorption spectra of 4-14 to 4-15 during the
titration with SbCl
5
in dry DCM
111
Figure 4.11
UV-vis-NIR absorption spectra of the oxidized pieces 4-14 and
4-15 during reduction by Zn with different contact time
112
Figure 4.12
Photo-stability test of compounds 4-1, 4-2, 4-14 and 4-15 in
toluene upon irradiation of 4 W UV light (emitting at 254 nm)
113
Figure 5.1
Molecular appoaches towards BODIPY dyes with longer
absorption and emmision
125
Figure 5.2
(a) UV-vis-NIR absorption spectra of 5-1b and 5-5b in toluene

(1.0 x 10
-5
M) and photoluminescence (PL) spectrum (1 x 10
-6

M) of compounds 5-1b in toluene (excitation wavelength is 670
nm). (b) Photoluminescence spectra of 5-1b in different solvents
(1.0 x 10
-6
M). (c) Concentration dependence of fluorescence
spectra of 5-1b in toluene (excitation wavelength = 670 nm). (d)
Concentration dependence of fluorescence spectra of 5-1b in
129


xvi
toluene (excitation wavelength = 670 nm)
Figure 5.3
Cyclic voltammograms of compounds 5-1b and 5-5b in DCM
132
Figure 5.4
Optimized structures and frontier molecular orbital profiles of
compound 5-1b (the arrow indicates the dipole moment)
133
Figure 5.5
Photo-stability test of compounds 3-2, 4-1 and 5-1b in toluene
upon irradiation of 4 W UV light (emitting at 254 nm)
134
Figure 5.6
Structures of BODIPY-fused porphyrins 148

Figure 5.7
UV-vis-NIR absorption spectra of 5-9, 5-10, 5-13 and 5-16 in
toluene (1.0 x 10
-5
M)
153
Figure 5.8
Cyclic voltammograms and differential pulse voltammogram of
compounds 5-9, 5-10, 5-13 and 5-16 in DCM
154
Figure 5.9
Changes of optical density of 5-9 and 5-10 at the absorption
maximum wavelength with the irradiation time
156
Figure 6.1
Molecular design and structures of dyes 6-1 and 6-2
171
Figure 6.2
UV-vis-NIR absorption spectra of 6-1 and 6-2 in CHCl
3
(8.0 x
10
-6
M)
174
Figure 6.3
Cyclic voltammograms (CV) and differential pulse
voltammograms (DPV) of compounds 6-1 and 6-2 in DCM
175
Figure 6.4

Frontier molecular orbital profiles of compounds 6-1 and 6.2
177
Figure 6.5
(A) IPCE spectra of the devices sensitized by 6-1 and 6-2. (B)
J-V curves of DSCs based on 6-1 and 6-2 at an irradiation of 100
mW cm
−2
AM1.5G Sunlight
178



xvii
LIST OF SCHEMES

Scheme 1.1
Synthesis of quarterrrylene derivative 1-4
4
Scheme 1.2
Synthesis of perylene derivatives 7
Scheme 1.3
Synthesis of bisanthene bis(dicarboximide) 8
Scheme 1.4
“Push-pull” rylene dyes 11
Scheme 1.5
Structures of rylene monoimide and their quinoidal species 13
Scheme 1.6
Synthesis of triply linked porphyrin tapes 17
Scheme 2.1
Synthetic scheme towards “push-pull” dyes 33

Scheme 3.1
Synthetic scheme towards rylenes 3-1 to 3-2
55
Scheme 3.2
Synthetic scheme towards quarterrylene bisimide 58
Scheme 4.1
Synthesis of NP fused porphyrins 81
Scheme 4.2
Synthesis of perylene monoimide-fused porphyrins 106
Scheme 5.1
Synthesis of perylene-fused BODIPY dye 126
Scheme 5.2
Synthesis of BODIPY-fused porphyrins 150
Scheme 6.1
Synthesis of perylene anhydride-fused porphyrins 173





xviii
LIST OF TABLES

Table 2.1
Summary of absorption and emission properties of dyes 2-1 to
2-4
35
Table 2.2
Summary of solvatochromic behaviors of dyes 2-1 to 2-4
38

Table 2.3
Summary of electrochemical properties of dyes 2-1 to 2-4
40
Table 3.1
Summary of Photophysical and electrochemical properties of
compounds 3-1 and 3-2
61
Table 4.1
Summary of photophysical and electrochemical properties of
compounds 4-1 and 4-2
87
Table 4.2
Summary of photophysical and electrochemical properties of
compounds 4-14 and 4-15
110
Table 5.1
Summary of electrochemical properties of compounds 5-1b and
5-5b
130
Table 5.2
Summary of electrochemical properties of compounds 5-9, 5-10,
5-13 and 5-16
155
Table 6.1
Summary of optical and electrochemical properties of
compounds 6-1 and 6-2
176


1

Chapter 1 Introduction

1.1 Introduction
Dye chemistry is believed to be one of the most explored areas in industrial
organic chemistry. Current developments in the field of electronics and in the area
of bioimaging have boosted interest in the development of next-generation
functional dyes. A recent rising interest is the design and synthesis of so-called
near infrared (NIR) dyes
1
which function (absorption and/or emission) in the NIR
spectral region ranging from 700 nm to 2000 nm owing to their diverse
applications. For instance, for practical applications such as solar cells, the
materials should have good light harvesting capability not only at UV-Vis spectral
range, but also at the NIR range given that sunlight possesses 50% of its radiation
energy in infrared region. On the other hand, biological samples have low
background fluorescence signals, and a concomitant high signal to noise ratio in
the NIR region. Moreover, NIR light can penetrate into sample matrices deeply
due to low light scattering. Thus, NIR dyes are required for various advanced
technologies, including high-contrast bio-imaging,
2
optical recording,
3
NIR laser
filter,
4
NIR photography,
5
solar cells,
6
and optical limiting at telecommunication

wavelength.
7
Up to now, very comprehensive range of common NIR compounds
(e.g. cyanines, polyenes, rare earth compounds, quantum dots) has been known,
some of which have even been commercialized. However, many commercially
available NIR dyes such as cyanine and polyene dyes suffer from inherent


2
drawbacks due to their insufficient photostability.
8
Additionally, some NIR
dyes/pigments also suffer from poor solubility for practical applications. To
circumvent such issues, design and synthesis of soluble and stable organic NIR
dyes are highly desirable for organic chemists.
Apart from commercialized dyes, another extraordinary class of compounds,
named polycyclic aromatic compounds such as polycyclic aromatic hydrocarbons
(PAHs, also known as nanographenes), porphyrins, and BODIPY
(4,4-difluoro-4-bora-3a,4a-diaza-s-indacene), are of great interest due to their
particular electronic and self-assembling properties, which can be exploited in
organic electronic devices such as field-effect transistors and solar cells.
9

Compared with traditional cyanine and polyene dyes, polycyclic aromatics usually
exhibit excellent chemical stability and photostability. In addition, polycyclic
aromatics hold the advantages such as low toxicity and ease of functional and
structural tunability over quantum dots. Therefore, polycyclic aromatics appear to
be promising candidates for NIR dyes. However, most polycyclic aromatics are
only capable of capturing the UV or visible light. Promotion of their absorptions
into NIR region can normally be achieved by extension of the π-conjugation or by

construction of push-pull motif or in rare cases by quinoidization. All the three
methods will definitely lower the HOMO-LUMO band gaps of the molecules and
lead to bathochromic shift of their absorption and emission bands. Another
troublesome issue for polycyclic aromatics (in particular, PAH) is their poor
solubility and this problem becomes more and more serious upon an increase of


3
the π-conjugation and the molecular size. In most cases, in order to resolve the
solubility problem, the attachment of long alkyl chains and/or induced distortion
from planarity of the aromatic core is highly desirable.

1.2 Literature review
1.2.1 Rylene derivatives
In pursuit of stable dyes with high extinction coefficients and
long-wavelength absorption/emission, rylenes have received a great deal of
attention. Rylenes are large polycyclic aromatic hydrocarbons in which two or
more naphthalene units are peri-fused together by single bonds. Only one
aromatic sextet benzenoid ring can be drawn for each naphthalene units and two
zig-zag edges exist at the terminal naphthalene units (Figure 1.1).
1-1a n=0,Perylene
1-1b n=1,Terrylene
1-1c n=2,Quaterrylene
1-1d n=3,Pentarylene
1-1e
n=4,Hexarylene
n n

Figure 1.1 A general structure of rylene molecules.

Perylene 1-1a, the first member of the perylene series (n = 0), has been
intensively studied due to its outstanding chemical, thermal and photochemical
inertness, its nontoxicity and low cost.
10
Extension of the conjugation length along
the long molecular axis of perylene by incorporation of additional naphthylene
units to form its higher homologue has proven to be an effective method to obtain


4
long wavelength absorbing rylene dyes. For example, terrylene 1-1b (n = 1)
11
and
quaterrylene 1-1c
12
absorb in the visible region with absorption maxima at 560 nm
and 662 nm, respectively. In search of mild conditions to synthesize higher rylenes,
a variety of intramolecular cyclodehydrogenation methods have been developed.
These include oxidative cyclodehydrogenation using FeCl
3
, or a combination of
CuCl
2
-AlCl
3
as Lewis acid as well as oxidant, and reductive
cyclodehydrogenation via anion radical mechanism promoted by base. A typical
example involving both processes is the synthesis of a quaterrrylene derivative 1-4
(Scheme 1.1). Singly linked precursor 1-2 successively underwent reductive
cyclodehydrogenation to generate partially cyclized intermediate 1-3 and

subsequent oxidative cyclodehydrogenation to give final quaterrrylene 1-4.
13
Four
tert-butyl groups were designed to resolve the solubility problem resulting from
the strong tendency of this ladder-type molecule to form aggregates.
K/DME
CuCl
2
-AlCl
3
1-2 1-3 1-4
Scheme 1.1 Synthesis of quarterrrylene derivative 1-4.

Since higher order rylenes are electron-rich π-systems and are relatively
unstable upon exposure to air, electron-withdrawing groups such as dicarboxylic