Synthesis and photovoltaic properties of formyl end-capped oligothiophenes

Article abstract of DOI:10.1080/00397910802654849

For the purpose of developing novel photovoltaic materials, 5,5″-biformyl-2,2′:5′,2″-terthiophene (OHC-3T-CHO) and 5,5″-biformyl-2,2′:5′,2″:5″,2?:5?, 2″″-q-uinquethiophene (OHC-5T-CHO) were synthesized. The photovoltaic properties of OHC-3T-CHO and OHC-5T-CHO were studied. We have fabricated two flexible organic photovoltaic devices using OHC-3T-CHO, OHC-5T-CHO, and 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA). The PET-ITO (indium tin oxides coated with polyethylene terephthalate)/OHC-3T-CHO/ PTCDA/Al device has an open circuit voltage (V_oc) of 1.12V, and photoelectric conversion efficiency (PCE) of 1.00%, whereas the PET-ITO/OHC-5T-CHO/PTCDA/Al device has a V_oc of 1.78V and PCE of 1.08%. Both devices have high V_oc (1.12V and 1.78V). It is possible that intermolecular hydrogen bonding between the -CHO group of OHC-nT-CHO and the carboxylic dianhydride of PTCDA enhanced the efficiency by promoting forward interfacial electron transfer.

Full text of DOI:10.1080/00397910802654849

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Synthesis and Photovoltaic
Properties of Formyl End-
Capped Oligothiophenes
Chuanyu Jiang a , Ping Liu a & Wenji Deng b
a Research Institute of Materials Science, South
China University of Technology , Guangzhou, China
b Department of Applied Physics , South China
University of Technology , Guangzhou, China
Published online: 01 Jun 2009.
To cite this article: Chuanyu Jiang , Ping Liu & Wenji Deng (2009) Synthesis
and Photovoltaic Properties of Formyl End-Capped Oligothiophenes, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 39:13, 2360-2369, DOI: 10.1080/00397910802654849
To link to this article: http://dx.doi.org/10.1080/00397910802654849
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Synthetic Communications1, 39: 2360–2369, 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910802654849
Synthesis and Photovoltaic Properties
of Formyl End-Capped Oligothiophenes
Chuanyu Jiang,1 Ping Liu,1 and Wenji Deng2
1Research Institute of Materials Science, South China University
of Technology, Guangzhou, China
2Department of Applied Physics, South China University of Technology,
Guangzhou, China
Abstract: For the purpose of developing novel photovoltaic materials,
5,500-biformyl-2,20:50,200-terthiophene (OHC-3T-CHO) and 5,50000-biformyl-2,20:50,
200:500,2000:5000,20000-q-uinquethiophene (OHC-5T-CHO) were synthesized. The photo-
voltaic properties of OHC-3T-CHO and OHC-5T-CHO were studied. We have
fabricated two flexible organic photovoltaic devices using OHC-3T-CHO,
OHC-5T-CHO, and 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA). The
PET-ITO (indium tin oxides coated with polyethylene terephthalate)=OHC-3T-
CHO=PTCDA=Al device has an open circuit voltage (Voc) of 1.12 V, and photo-
electric conversion efficiency (PCE) of 1.00%, whereas the PET-ITO=OHC-5T-
CHO=PTCDA=Al device has a Voc of 1.78 V and PCE of 1.08%. Both devices have
high Voc (1.12 V and 1.78 V). It is possible that intermolecular hydrogen bonding
between the –CHO group of OHC-nT-CHO and the carboxylic dianhydride of
PTCDA enhanced the efficiency by promoting forward interfacial electron transfer.
Keywords: Flexible organic photovoltaic devices, intermolecular hydrogen
bonding, oligothiophenes
INTRODUCTION
When Tang[1] discovered that bringing a donor and an acceptor together
in one cell could dramatically increase power conversion efficiency
Received September 24, 2008.
Address correspondence to Ping Liu, Research Institute of Materials Science,
South China University of Technology, Guangzhou 510640, China. E-mail:
mcpliu@scut.edu.cn
2360

Formyl End-Capped Oligothiophenes
2361
Scheme 1. Molecular structures of PTCDA, OHC-3T-CHO, and OHC-5T-CHO.
(PCE), a major breakthrough came in the field of organic photovoltaics.
The concept of heterojunction has since been widely exploited in dye–dye,
polymer–dye, polymer–polymer, and polymer–fullerene blend photovol-
taic devices. Recently, power conversion efficiencies of more than 6%[2]
of organic photovoltaic devices employing polymer–fullerene blends have
been achieved through variations in the processing techniques. However,
most of these organic photovoltaic devices were processed on rigid glass
substrates. Development of flexible and lightweight organic photovoltaic
devices has become an interesting subject.
As models of polythiophenes, oligothiophenes and their derivatives
have received considerable attention because of their fascinating optical
and electrochemical properties. Oligothiophenes and their derivatives
have been widely studied as functional materials in the fields of
field-effect transistors (FET),[3] light-emitting diodes,[4] photovoltaic
devices,[5] liquid crystals,[6] and electrochromics.[7]
In this article, we address the aim of developing new photovoltaic
materials based on oligothiophenes. We herein report the synthesis of
5,500-biformyl-2,20:50,200-terthiophene (OHC-3T-CHO) and 5,50000-biformyl-
2,20:50,200:500,2000:5000,20000-quinquethiophene (OHC-5T-CHO) (Scheme 1). The
photovoltaic properties of OHC-3T-CHO and OHC-5T-CHO were studied.
RESULTS AND DISCUSSION
OHC-3T-CHO was synthesized throught the reaction of 2,20:50,200-
terthiophene (3T) with phosphorus oxychloride (POCl3) and dimethylfor-
mamide (DMF) under microwave irradiation. OHC-5T-CHO was synthe-
sized throught the reaction of 2,20:50,200:500,2000:5000,20000-quinquethiophene
(5T) with POCl3 and DMF under microwave irradiation. 3,4,9,10-
Perylenetetracarboxylic dianhydride (PTCDA) was commercially available.
PET-ITO was used as flexible substrate.

2362
C. Jiang, P. Liu, and W. Deng
For most of the conjugated compounds, the absorbance in the visible
region of the thin film of the compound is an important parameter when
they are used as photovoltaic materials. Figure 1 shows the electronic
absorption spectras of the vacuum-deposited OHC-3T-CHO, OHC-5T-
CHO, and PTCDA films. OHC-3T-CHO film absorbs light in the
wavelength range of 240–670 nm, OHC-5T-CHO film absorbs light in
the wavelength range of 350–660 nm, and PTCDA film absorbs light
in the wavelength range of 400–640 nm. All of the wavelength ranges
are useful for photovoltaic conversion. Therefore, it is expected that the
devices consisting of OHC-3T-CHO, OHC-5T-CHO, and PTCDA may
respond to ultraviolet–visible (UV-vis) light over a wide wavelength
region.
Electrochemical cyclic voltammetry was performed for determining
the energy levels of the highest occupied molecular orbital (HOMO)
and the lowest unoccupied molecular orbital (LUMO) of conjugated
compounds. The cyclic voltammograms of OHC-3T-CHO and OHC-5T-
CHO were done in the solution of tetra-n-butylammonium perchlorate
(0.1 mol=L) in dichloromethane, and an Ag=Agþ electrode was used as
reference electrode. Both OHC-3T-CHO and OHC-5T-CHO exhibited
one anodic oxidation and one cathodic wave. The first onset of oxidation
potential and the first onset of reduction potential were 1.06V and ꢀ0.62V
vs. Ag=Agþ for OHC-3T-CHO and 0.97V and ꢀ0.51V vs. Ag=Agþ
for OHC-5T-CHO. According to literature, PTCDA exhibited one anodic
oxidation and one cathodic wave.[8] The first oxidation potential and the
Figure 1. Electronic absorption spectra of the vacuum-deposited OHC-3T-CHO,
OHC-5T-CHO, and PTCDA films.

Formyl End-Capped Oligothiophenes
2363
first reduction potential were 2.29V and ꢀ0.05V vs. Ag=Agþ for PTCDA.
HOMO and LUMO energy levels were calculated according to the
following equations[9]:
HOMO ¼ ꢀe ðEox þ 4:71Þ ðeVÞ
LUMO ¼ ꢀe ðEred þ 4:71Þ ðeVÞ
where the unit of potential is V vs. Ag=Agþ. The HOMO energy levels of
OHC-3T-CHO, OHC-5T-CHO, and PTCDA were ꢀ5.77eV, ꢀ5.68eV,
and ꢀ7.00eV, respectively. The LUMO energy levels of OHC-3T-CHO,
OHC-5T-CHO, and PTCDA were ꢀ4.09eV, ꢀ4.20eV, and ꢀ4.66eV,
respectively. Figure 2 clearly shows that the LUMO of PTCDA is less
than the LUMO of OHC-3T-CHO and OHC-5T-CHO. If OHC-3T-
CHO and OHC-5T-CHO were candidates as electron-donor materials,
and PTCDA were candidates as the electron-acceptor material, they would
match well and might exhibit good photovoltaic properties.
To check the photovoltaic properties of OHC-3T-CHO and OHC-5T-
CHO, we fabricated two flexible photovoltaic devices, PET-ITO=OHC-3T-
CHO=PTCDA=Al and PET-ITO=OHC-5T-CHO=PTCDA=Al. Flexible
PET-ITO film was commercially available. The organic layers of OHC-3T-
CHO, OHC-5T-CHO and PTCDA were deposited by vacuum deposition
(vacuum pressure 4 ꢁ 10ꢀ3 Pa). The thicknesses of OHC-3T-CHO,
OHC-5T-CHO, and PTCDA films were about 80–100 nm, 80–100 nm,
and 80–100 nm, respectively. A solar simulator (CMH-250, Aodite
Photoelectronic Technology Ltd., Beijing) with light intensity of
78.2 mW=cm2 was used as light source. Figure 3 shows the I–V curves of
the two flexible devices PET-ITO=OHC-3T-CHO=PTCDA=Al and
Figure 2. Energy level of OHC-3T-CHO, OHC-5T-CHO, and PTCDA.

2364
C. Jiang, P. Liu, and W. Deng
Figure 3. I–V curves of the two flexible devices under the illumination of
78.2 mW=cm2 simulated sunlight through the PET-ITO electrode.
PET-ITO=OHC-5T-CHO=PTCDA=Al under the illumination of
78.2 mW=cm2 simulated sunlight, and the photovoltaic properties are listed
in Table 1. The PET-ITO=OHC-3T-CHO=PTCDA=Al device has an open
circuit voltage (Voc) of 1.12 V and photoelectric conversion efficiency (PCE)
of 1.00%, whereas the PET- ITO=OHC-5T-CHO=PTCDA=Al device has an
open circuit voltage (Voc) of 1.78V and PCE of 1.08%. The Voc of
PET-ITO=OHC-5T-CHO=PTCDA=Al device is greater than that of the
PET-ITO=5T-CHO=PTCDA=Al device (1.70 V)[10] under the same condi-
tion. Therefore, we supposed that the intermolecular hydrogen bonding
between OHC-nT-CHO and PTCDA is stronger than the interaction of
intermolecular hydrogen bonding between nT-CHO and PTCDA. The
presence of intermolecular hydrogen bonding had been evidenced by
Table 1. Photovoltaic properties of the two flexible
devices under the illumination of 78.2 mW=cm2 simu-
lated sunlight through the PET-ITO electrode
Parameter
OHC-3T-CHO
OHC-5T-CHO
Voc(V)
1.12
1.58
44.30
1.00
1.78
1.32
36.05
1.08
Isc(mA cmꢀ2
FF(%)
PCE(%)
)

Formyl End-Capped Oligothiophenes
2365
infrared (IR) absorption spectroscopy. The OHC-5T-CHO showed only an
absorption around at 1655cmꢀ1, which is attributable to the stretching
vibration of the free H-C¼O, whereas the mixture of OHC-5T-CHO=
PTCDA showed the hydrogen-bonded absorption band at 1646 cmꢀ1
,
which is attributable to the stretching vibration of the hydrogen-bonded
H-C¼O. Intermolecular hydrogen bonding between the –CHO group of
OHC-nT-CHO and the carboxylic dianhydride of PTCDA enhanced the
efficiency by promoting forward interfacial electron transfer.
CONCLUSION
For the purpose of developing novel photovoltaic materials, 5,500-
biformyl-2,20:50,200-terthiophene (OHC-3T-CHO) and 5,50000-biformyl-
2,20:50,200:500,2000:5000,20000-quinquethiophene (OHC-5T-CHO) were synthe-
sized. The photovoltaic properties of OHC-3T-CHO and OHC-5T-CHO
were studied. Under the illumination of 78.2 mW=cm2 simulated sunlight,
The PET-ITO=OHC-3T-CHO=PTCDA=Al device has an open circuit vol-
tage (Voc) of 1.12V and of 1.00%, whereas the PET-ITO=OHC-5T-
CHO=PTCDA=Al device has an open circuit voltage (Voc) of 1.78 V and
PCE of 1.08%. Both of the two devices have high Voc (1.12 V and 1.78 V).
It is possible that intermolecular hydrogen bonding between the –CHO
group of OHC-nT-CHO and the carboxylic dianhydride of PTCDA
enhanced the efficiency by promoting forward interfacial electron transfer.
EXPERIMENTAL
Synthesis
2-Bromothiophene, 2,5-dibromothiophene, [1,3-bis-(diphenyphosphino)
propane] nickel(II) chloride [NiCl2–(dppp)], magnesium, phosphorus
oxychloride (POCl3), and DMF were commercially available and used
without further purification. Tetrahydrofuran (THF) was dried over
Na=benzopheneone ketyl and freshly distilled prior to use. 2,20:50,200-
Terthiophene (3T) was prepared by the Grignard coupling reaction of
2,5-dibromothiophene with 2-bromomagnesiumthiophene in THF.
Synthetic procedures are illustrated in Scheme 2.
Synthesis of 5,500-Biformyl-2,20:50,200-terthiophene (OHC-3T-CHO)
OHC-3T-CHO was synthesized as follows. Phosphorus oxychloride
(POCl3) (20 ml, 217.8 mmol) was added to DMF (50 ml) at room

2366
C. Jiang, P. Liu, and W. Deng
Scheme 2. Synthesis of OHC-3T-CHO and OHC-5T-CHO.
temperature. DMF was used as solvent and reagent. The mixture was
stirred at 45ꢂC under microwave irradiation (400 W) for 25 min. Then
2,20:50,200-terthiophene (3T) (2.3 g, 9 mmol) was added to the DMF solu-
tion of POCl3. The reaction mixture was stirred at 45ꢂC under microwave
irradiation (400 W) for 25 min, then stirred at 65ꢂC under microwave irra-
diation (400 W) for 30 min. The reaction mixture was cooled, dropped
into water, and extracted with chloroform. The organic layer was washed
with water, separated three times, and dried with Na2SO4. The solvent
was removed by evaporation after filtration, and the residue was purified
by silica-gel column chromatograph using toluene as eluent (1.89 g, yield
67%). MS (EI) m=z: 303.8 (Mþ); 1H NMR (CDCl3, 400 MHz). d: 9.86 (s,
2H), 7.67 (d, 2H), 7.30 (s, 2H); 7.28 (d, 2H); 13C NMR (CDCl3,
400 MHz), d: 182.32, 142.48, 137.26, 137.02, 127.03, 124.97, 124.80;
FT-IR (KBr, cmꢀ1): 3066 (nC–H), 1655 (nC¼O); UV-vis (CHCl3): kambasx
413 nm.
Synthesis of 5,500-Dibromo-2,20:50,200-terthiophene (DBr3T)
2,20:50,200-Terthiophene (3T, 2.5 g, 10.07 mmol) was dissolved in 300 ml of
CHCl3. Then N-bromosuccinimide (NBS, 5.38 g, 30.23 mmol) was added
to the solution. The reaction mixture was stirred overnight before wash-
ing with hydrochloric acid, then separated five times, and dried with
Na2SO4. The solvent was removed by evaporation after filtration, and
the residue was subjected to the next step without further purification.
Synthesis of 2,20:50,200:500,2000:5000,20000-Quinquethiophene (5T)
2,20:50,200:500,2000:5000,20000-Quinquethiophene (5T) was prepared by the
Grignard coupling reaction of DBr3T with 2-bromomagnesiumthiophene

Formyl End-Capped Oligothiophenes
2367
in THF. Magnesium turnings (Mg, 1.4 g, 82.3 mol) were added to THF
(15 ml). Then 2-bromothiophene (9.63 g, 59.01 mmol) was added to the
mixture. The reaction mixture was allowed to stir at reflux for 40 min
before being cooled back to room temperature and then stirred at room
temperature for 3 h, giving 2-bromomagnesiumthiophene for use.
DBr3T (3 g, 7.38mmol) and THF (20 ml) were put into another
flask, and [1,3-bis-(diphenyphosphino) propane] nickel(II) chloride
[NiCl2(dppp)] was added to the reaction mixture as catalyzer. The 2-bromo-
magnesiumthiophene prepared previously was added to the mixture. The
reaction mixture was stirred overnight. The solvent was removed by eva-
poration, and the residue was purified by silica-gel column chromatography
using petroleum ether as eluent (1.31 g, yield 43%). MS (EI) m=z: 411.9
1
(Mþ); H NMR (CDCl3, 400 MHz). d: 7.39 (s, 2H), 7.26 (d, 2H), 7.17
(d, 2H), 7.08–7.06 (m, 4H), 7.02 (t, 2H); 13C NMR (CDCl3, 400 MHz), d:
136.04, 135.57, 134.67, 130.28, 128.04, 127.85, 126.59, 125.55, 124.48,
124.44; UV-vis (CHCl3): kambasx 410 nm.
Synthesis of 5,50000-Biformyl-2,20:50,200:500,2000:5000,20000-quinquethiophene
(OHC-5T-CHO)
OHC-5T-CHO was synthesized as follows. Phosphorus oxychloride (POCl3)
(12 ml, 130.6mmol) was added to DMF (30ml) at room temperature. DMF
was used as solvent and reagent here. The mixture was stirred at 45ꢂC
under microwave irradiation (400 W) for 25 min, and then 2,20:50,200:500,
2000:5000,20000-quinquethiophene (5T) (0.15g, 0.36mmol) was added to the
DMF solution of POCl3. The reaction mixture was stirred at 45ꢂC
under microwave irradiation (400W) for 25min, and then stirred at 65ꢂC
under microwave irradiation (400 W) for 40 min. The reaction mixture
was cooled, dropped into water, and extracted with chloroform. The organic
layer was washed with water, separated three times, and dried with Na2SO4.
The solvent was removed by evaporation after filtration, and the residue
was purified by silica-gel column chromatograph using toluene as eluent
(0.08 g, yield 48%). MS (EI) m=z: 467.4 (Mþ); 1H NMR (CDCl3,
400 MHz). d: 9.86 (s, 2H), 7.67 (t, 2H), 7.40 (d, 2H), 7.28 (d, 2H),
7.20–7.16 (m, 4H); 13C NMR (CDCl3, 400 MHz), d: 181.89, 136.88,
134.44, 132.25, 130.46, 129.72, 128.17, 127.03, 125.25, 124.44, 121.31; FT-IR
(KBr, cmꢀ1): 3082 (nC–H), 1655 (nC¼O); UV-vis (CHCl3): kmabasx 450 nm.
Characterization
The reactions were performed under microwave irradiation (XH-100A
microwave catalysing synthesizer, XiangHu Science and Technology

2368
C. Jiang, P. Liu, and W. Deng
Development Co., Ltd. Beijing). 1H NMR spectra and 13C NMR spectra
were recorded on a Bruker Avanece 400 spectrometer in CDCl3 or tetra-
hydrofuran (THF-d8). UV-vis spectra were recorded on a Thermo
Helios-y instrument. Mass spectra (MS) were recorded on a Shimadzu
GCMS-QP-2010. Fourier transform (FT)–IR spectra were recorded on
a Bruker Tensor 27. Cyclic voltammetry was carried out on a CHI-750-A
voltammetric analyzer (Zhenhua Apparatus Co., Ltd, Shanghai). I–V
curves were obtained from a Keithlet 2400 Source Meter.
ACKNOWLEDGMENTS
This work was supported by the Ministry of Science and Technology of
China (National Key Program for Basic Research, No. 2001-CCA03500)
and the Natural Science Foundation of China NSFC (nos. 20674022,
20534020, and 20774031). We also thank the Natural Science Founda-
tions of Guangdong (Nos. 04105931 and 2006A10702003) and
Guangzhou (No. 2004J1-C0041) for financial support.
REFERENCES
1. Tang, C. W. Two-layer organic photovoltaic cell. Appl. Phys. Lett. 1986, 48,
183–185.
2. Kim, J. Y.; Lee, K.; Coate, N. E.; Moses, D.; Nguyen, T. Q.; Dante, M.;
Heeger, A. J. Efficient tandem polymer solar cells fabricated by all-solution
processing. Science 2007, 317, 222–225.
3. (a) Li, W. J.; Katz, H. E.; Lovinger, A. J.; Laquindanum, J. G. Field-effect
transistors based on thiophene hexamer analogues with diminished electron
donor strength. Chem. Mater. 1999, 11, 458–465; (b) Meng, H.; Zheng, J.;
Lovinger, A. J.; Wang, B. C.; Patten, P. G. V.; Bao, Z. N. Oligofluorene–
thiophene derivatives as high-performance semiconductors for organic thin
film transistors. Chem. Mater. 2003, 15, 1778–1787; (c) Chang, P. C.; Lee, J.;
Subramanian, V.; Murphy, A. R.; Frechet, J. M. J. Film morphology and
thin film transistor performance of solution-processed oligothiophenes.
Chem. Mater. 2004, 16, 4783–4789; (d) Lim, E.; Jung, B. J.; Shim, H. K.;
Taguchi, T.; Nodo, B.; Kambayashi, T.; Mori, T.; Ishikawa, K.; Takezoe, H.;
Do, L. M. Nanoscale thin-film morphologies and field-effect transistor
behavior of oligothiophene derivatives. Org. Electron. 2006, 7, 121–131;
(e) Ohshita, J.; Izumi, Y.; Kim, D. H.; Kunai, A.; Kosuge, T.; Kunugi, Y.;
Naka, A.; Ishilawa, M. Applications of silicon-bridged oligithiophenes to
organic FET materials. Organometallics 2007, 26, 6150–6154.
4. (a) Shin, D. M.; Lim, S. T.; Choi, J. S.; Kim, J. S. Influence of oligothiophene
layer on the light emitting efficiency. Thin Solid Films. 2000, 363, 268–270; (b)
Mazzeo, M.; Pisignano, D.; Favaretto, L.; Barbarella, G.; Cingolani, R.;

Formyl End-Capped Oligothiophenes
2369
Gigli, G. Bright oligothiophene-based light emitting diodes. Synth. Metals
2003, 139, 671–673.
5. (a) Tan, S. X.; Zhai, J.; Fang, H. J.; Jiu, T.G.; Ge, J.; Li, Y. L.; Jiang, L.;
Zhu, D. B. Novel carboxylated oligothiophenes as sensitizers in photoelectric
conversion systems. Chem. Eur. J. 2005, 11, 6272–6276; (b) Liu, P.; Pan,
W. Z.; Huang, M. S.; Deng, W. J. Organic photovoltaic properties based on
oligothiophenes. Chin. Chem. Lett. 2006, 17, 903–906; (c) Liu, P.; Huang, J.
L.; Pan, W. Z.; Huang, M. S.; Deng, W. J.; Mai, Y. L.; Luan, A. B. Organic
photovoltaic devices with high open-circuit voltage based on oligothiophene
derivatives. Chin. Chem. Lett. 2007, 18, 437–440; (d) Negishi, N.; Takimiya,
K.; Otsubo, T.; Harima, Y.; Aso, Y. Oligothiophene–multifullerene linkage
molecules as high performance photovoltaic materials. Synth. Metals 2005,
152, 125–128.
6. (a) Liu, P.; Zhang, Y. M.; Feng, G. J.; Hu, J. H.; Zhou, X. P.; Zhao, Q. Z.;
Xu, Y. H.; Tong, Z.; Deng, W. J. Synthesis and liquid crystal properties of a
novel family of oligothiophene derivatives. Tetrahedron 2004, 60, 5259–5264;
(b) Liu, P.; Liu, M. M: Deng, W. J. Synthesis and mesogenic properties of
novel terthiophene derivatives. Synth. Commun. 2006, 36, 685–692; (c)
Azumi, R.; Gotz, G.; Bauerle, P.; Bauerle, P. Thermal behavior of a-alkylated
igothiophenes. Synth. Metals 1999, 101, 544–545; (d) Prehm, M.; Gotz, G.;
Bauerle, P.; Liu, F.; Zeng, X. B.; Unhar, G.; Tschierske, C. Complex
liquid-crystalline superstructure of a p-conjugated oligothiophene. Angew.
Chem. 2007, 119, 8002–8005; (e) Leroy, J.; Boucher, N.; Sergeyev, S.;
Sferrazza, M.; Geerts, Y. H. Symmetrical and nonsymmetrial liquid
crystalline oligothiophenes: Convenient synthesis and transition-temperature
engineering. Eur. J. Org. Chem. 2007, 1256–1261.
7. Imae, I.; Nawa, K.; Ohsedo, Y.; Noma, N.; Shirota, Y. Synthesis of a novel
family of electrochemically doped vinyl polymers containing pendant
oligothiophenes and their electrical and electrochromic properties. Macromo-
lecules 1997, 30, 380–386.
8. Slattery, D. K.; Linkous, C. A.; Gruhn, N. E.; Baum, C. Semiempirical MO
and voltammetric estimation of ionization potentials of organic pigments:
Comparison to gas phase ultraviolet photoelectron spectroscopy. Dyes Pigm.
2001, 49, 21–27.
9. Hou, J. H.; Tan, Z. A.; Yan, Y.; He, Y. J.; Yang, C. H.; Li, Y. F. Synthesis and
photovoltaic properties of two-dimensional conjugated polythiophenes with
bi(thienylenevinylene) side chain. J. Am. Chem. Soc. 2006, 128, 4911–4916.
10. Liu, P.; Chen, T. H.; Pan, W. Z.; Huang, M. S.; Deng, W. J.; Mai, Y. L.;
Luan, A. B. Flexible organic photovoltaic devices based on oligothiophene
derivatives. Chin. Chem. Lett. 2008, 19, 207–210.