Synthesis and photovoltaic properties of two-dimensional D-A copolymers with conjugated side chains

Article abstract of DOI:10.1002/pola.24823

Four novel two-dimensional (2D) donor-acceptor (D-A) type copolymers with different conjugated side chains, P1, P2, P3, and P4 (see Fig. 1), are designed and synthesized for the application as donor materials in polymer solar cells (PSCs). To the best of

Full text of DOI:10.1002/pola.24823

Synthesis and Photovoltaic Properties of Two-Dimensional D-A
Copolymers with Conjugated Side Chains
DUGANG CHEN,1 YANG YANG,2 CHENG ZHONG,1 ZHENGRAN YI,1 FEI WU,1 LI QU,1 YU LI,1 YONGFANG LI,2 JINGUI QIN1
1Department of Chemistry and Hubei Key Lab on Organic and Polymeric Optoelectronic Materials, Wuhan University,
Wuhan 430072, China
2Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, Institute of Chemistry,
Chinese Academy of Sciences, Beijing 100190, China
Received 12 February 2011; accepted 6 June 2011
DOI: 10.1002/pola.24823
Published online 29 June 2011 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: Four novel two-dimensional (2D) donor–acceptor
(D-A) type copolymers with different conjugated side chains,
P1, P2, P3, and P4 (see Fig. 1), are designed and synthesized
for the application as donor materials in polymer solar cells
(PSCs). To the best of our knowledge, there were few reports
to systematically study such 2D polymers with D-A type main
chains in this area. The optical energy band gaps are about 2.0
eV for P1–P3 and 1.67 eV for P4. PSC devices using P1–P4 as
donor and [6,6]-phenyl-C61-butyric acid methyl ester as
acceptor in a weight ratio of 1:3 were fabricated and character-
ized to investigate the photovoltaic properties of the polymers.
Under AM 1.5 G, 100 mA/cm2 illumination, a high open-circuit
voltage (Voc) of 0.9 V was recorded for P3-based device due to
its low HOMO level, and moderate fill factor was obtained with
the best value of 58.6% for P4-based device, which may mainly
be the result of the high hole mobility of the polymers (up to
1.82 ꢀ 10ꢁ3 cm2/V s).
2011 Wiley Periodicals, Inc. J Polym
C
V
Sci Part A: Polym Chem 49: 3852–3862, 2011
KEYWORDS: atomic force microscopy (AFM); electrochemistry;
hole mobility; polymer solar cells; synthesis; two-dimensional
conjugated polymers
INTRODUCTION Polymer solar cells (PSCs) have attracted
considerable attention as one of the next-generation solar
cells because of their advantages of low cost, light weight,
and their ability to form large and flexible devices.1–4 Solu-
tion-processed bulk heterojunction (BHJ) PSCs have been
proved to be the most successful device structure, which
typically use a two-component active layer consisting of an
electron-donating conjugated polymer and an electron-
accepting fullerene structured in a disordered bicontinuous
interpenetrating network.5–8 Ever since the BHJ photovoltaic
cells were first reported in 1995,9 the overall power conver-
sion efficiency (PCE) has steadily been improved from an ini-
tial 1% in the poly(phenylene vinylene) system,9 to 4–5% in
the poly(3-hexylthiphene) (P3HT) system,10,11 and to over
7% in copolymer with donor–acceptor (D-A) structure, as
reported recently.12,13 However, it is still necessary to
increase PCE for large-scale commercialization.
fact, several D-A type conjugated polymers with PCE as high
as 3ꢂ7% have been realized when they were blended with
[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) or [6,6]-
phenyl-C71-butyric acid methyl ester (PC71BM) in BHJ devi-
ces.14–21
Meanwhile, some two-dimensional (2D) polymers have also
been studied in PSCs,22–26 because it is well known that
extension of conjugation degree leads to enhancement and
red-shift of the absorption spectra of conjugated polymers.
As reported in literatures,22–26 the main chains of the 2D
polymers were all constructed by D-D type moieties, and
D-D or D-A type conjugated side chains were connected to
the backbone to form a much larger conjugated system.
These 2D polymers could make some advantages in light
absorption and the probability for p–p stacking. As a result,
good photovoltaic properties may be obtained.
Since the linear D-A type copolymers showed the highest
PCE until now,12 and introduction of conjugated side chains
could increase charge transport ability or extend the absorp-
tion range,22–26 we have planned to combine the advantages
of these two kinds of structure, namely, to design and to syn-
thesize novel 2D polymers with D-A type main chains and
various pendent conjugated side chains for application in
Nowadays, conjugated copolymers with alternating electron-
rich (donor) and electron-deficient (acceptor) moieties along
their backbone have been extensively studied.14–21 Their
absorption spectra, band gaps, and molecular energy levels
can be readily tuned by controlling the intramolecular charge
transfer (ICT) from the donor units to the acceptor units. In
Additional Supporting Information may be found in the online version of this article. Correspondence to: Y. Li (E-mail: liyf@iccas.ac.cn) or J. Qin
(E-mail: jgqin@whu.edu.cn)
C
V
Journal of Polymer Science Part A: Polymer Chemistry, Vol. 49, 3852–3862 (2011) 2011 Wiley Periodicals, Inc.
3852
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
FIGURE 1 Chemical Structure of the Polymers P1–P4.
PSCs. As a result, four new 2D polymers were designed
(their structures are shown in Fig. 1). This article will report
the synthesis, thermal, optical, electrical, and photovoltaic
properties of the polymers. The relationship between the
structure and the properties will also be discussed. To the
best of our knowledge, there were few reports to systemati-
cally study such 2D polymers with D-A type main chains and
various pendent-conjugated side chains for application in
PSCs. Our interest is to explore a possibility of finding a new
approach for molecular design and better materials for PSCs.
microanalyzer. EI-MS spectra were recorded with a VJ-ZAB-
3F-Mass spectrometer. UV–vis absorption spectra were
recorded on a Shimadzu UV-2500 recording spectrophotome-
ter. Gel permeation chromatography (GPC) analysis was per-
formed on an Agilent 1100 series HPLC system equipped
with a G1326A refractive index detector, in which polysty-
rene standards were used as calibration standards and THF
was used as an eluent, and the flow rate was 1.0 mL/min.
Thermogravimetric analysis (TGA) was undertaken with a
NETZSCH STA 449C instrument. The thermal stability of the
samples under a nitrogen atmosphere was determined by
ꢃ
measuring their weight loss while heating at a rate of 10 C
EXPERIMENTAL
minꢁ1 from 30 to 500 ꢃC. Cyclic voltammetry (CV) was car-
ried out in nitrogen-purged anhydrous CH3CN solution at
room temperature with a CHI voltammetric analyzer. Tetra-
butylammonium hexafluorophosphate (TBAPF6; 0.1 M)
was used as the supporting electrolyte. The conventional
General
1H NMR and 13C NMR spectra were measured on a MER-
CURY-VX300 spectrometer. Elemental analysis of carbon,
hydrogen, and nitrogen was performed on a Vario EL III
SYNTHESIS AND PROPERTIES OF 2D D-A COPOLYMERS, CHEN ET AL.
3853

JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
three-electrode configuration consisted of a platinum work-
ing electrode, a platinum wire auxiliary electrode, and an Ag
wire pseudo-reference electrode with ferrocenium-ferrocene
(Fcþ/Fc) as the internal standard. Cyclic voltammograms
were obtained at a scan rate of 100 mV sꢁ1. Formal poten-
tials were calculated as the average of cyclic voltammetric
anodic and cathodic peaks. The onset potential was deter-
mined from the intersection of two tangents drawn at the
rising and background current of the cyclic voltammogram.
1.36–1.26 (m, 36H), 0.88 (t, J ¼ 6.0 Hz, 6H). 13C NMR
(CDCl3, 75 MHz) d (ppm): 152.73, 144.43, 139.09, 129.08,
126.12, 125.60, 121.60, 32.00, 30.73, 30.58, 29.75, 29.57,
29.45, 22.76, 14.18. Anal. Calcd for C38H56N2S3 (%): C,
71.64; H, 8.86; N, 4.40. Found: C, 71.36; H, 8.68; N, 4.52.
4,7-Bis(5-bromo-4-dodecylthiophen-2-yl)benzo[c][1,2,5]-
thiadiazole (M1)
Compound 3 (1.8 g, 2.83 mmol) was dissolved in a mixture
of chloroform (80 mL) and glacial acetic acid (80 mL). NBS
(1.06 g, 5.96 mmol) was then added to the solution and
stirred for 12 h in the dark. Much precipitate appeared dur-
ing the reaction. After the reaction, the mixture was poured
into water and extracted with chloroform. The organic
extracts were collected and dried with anhydrous Na2SO4.
After removal of the solvent, the crude product was purified
by column chromatography on silica gel using 1/1 (v/v) pe-
troleum ether/dichloromethane as eluent. Pure compound as
a deep red powder was obtained by recrystallization from n-
hexane.
Device Fabrication and Characterization of PSCs
PSCs were fabricated with ITO glass as a positive electrode,
Al as a negative electrode and the blend film of the poly-
mer/PCBM between them as a photosensitive layer. The ITO
glass was precleaned and modified by a thin layer of
PEDOT:PSS, which was spin-coated from a PEDOT:PSS aque-
ous solution (Clevious P VP AI 4083 H. C. Stark, Germany)
on the ITO substrate, and the thickness of the PEDOT:PSS
layer is about 60 nm. The photosensitive layer was prepared
by spin-coating a blend solution of polymers and PCBM in
chlorobenzene on the ITO/PEDOT:PSS electrode. Then, the Al
cathode was deposited on the polymer layer by vacuum
evaporation under 3 ꢀ 10ꢁ4 Pa. The thickness of the photo-
sensitive layer is about 80 nm, measured on an Ambios
Tech. XP-2 profilometer. The effective area of one cell is 4
mm2. The current–voltage (J–V) measurement of the devices
Yield: 1.91 g, 85%. 1H NMR (CDCl3, 300 MHz) d (ppm):
7.77–7.76 (m, 4H), 2.64 (t, J ¼ 7.5Hz, 4H), 1.68–1.64 (m,
4H), 1.36–1.26 (m, 36H), 0.88 (t, J ¼ 5.7 Hz, 6H). 13C NMR
(CDCl3, 75 MHz) d (ppm): 152.28, 143.25, 138.67, 128.20,
125.34, 124.89, 111.85, 32.19, 29.94, 29.73, 29.64, 22.97,
14.41. Anal. Calcd for C38H54Br2N2S3 (%): C, 57.42; H, 6.85;
N, 3.52. Found: C, 57.52; H, 6.76; N, 3.57.
was conducted on
a computer-controlled Keithley 236
Source Measure Unit. A xenon lamp with AM 1.5 filter was
used as the white light source, and the optical power at the
sample was around 100 mW/cm2.
Diethyl 4-(benzo[d]thiazol-2-yl)benzylphosphonate (5)
A mixture of 2-(4-(bromomethyl)phenyl)benzo[d]thiazole (4;
1 g, 3.29 mmol) and 5 mL of triethyl phosphite were heated
at 120 ꢃC for 16 h. Excess triethyl phosphite was removed
by vacuum distillation. The crude product was purified by
column chromatography (CHCl3) to give compound 5 as
white solid.
Materials
Toluene was dried over and distilled from K-Na alloy under
an atmosphere of argon. Compound 9 was purchased from
Sigma-Aldrich and used without further purification. The
starting materials and some intermediates (Compounds 1,27
2,28 4,29 6,30 7,31 8,32 M5,33 and M621) were synthesized
according to the literature procedures. Other reagents were
obtained from Sinopharm Chemical Reagent (Shanghai,
China).
Yield: 1 g, 85%. 1H NMR (CDCl3, 300 MHz) d (ppm): 8.09–
8.04 (m, 3H), 7.92 (d, J ¼ 8.1 Hz, 1H), 7.53–7.35 (m, 4H),
4.10–4.00 (m, 4H), 3.23 (d, J ¼ 22 Hz, 2H), 1.27 (t, J ¼ 6.9
Hz, 6H). 13C NMR (CDCl3, 75 MHz) d (ppm): 168.26, 153.28,
135.78, 134.69, 131.82, 130.72, 128.07, 126.83, 125.69,
123.14, 121.82, 62.48, 34.61, 33.68, 16.57. Anal. Calcd for
Monomer Synthesis
4,7-Bis(4-dodecylthiophen-2-yl)benzo[c][1,2,5]
thiadiazole (3)
C18H20NO3PS (%): C, 59.82; H, 5.58; N, 3.88. Found: C,
59.89; H, 5.42; N, 3.87. EI-MS: m/z 361.0 (Calcd: 361.1).
A mixture of 2-(4-dodecylthiophen-2-yl)-4,4,5,5-tetramethyl-
1,3,2-dioxaborolane (1; 3 g, 7.9 mmol), 4,7-dibromoben-
zo[c][1,2,5]thiadiazole (2; 1 g, 3.4 mmol), Pd (PPh3)4 (2%
mmol, 0.18 g), and K2CO3 (4.14 g, 30 mmol) in 40 mL of tol-
uene and 15 mL of distilled water was refluxed under argon
for 48 h. After the reaction, the resulting mixture was cooled
to room temperature and then poured into water and
extracted with ethylether. The organic extracts were collected
and dried with anhydrous Na2SO4. After removal of the sol-
vent, the crude product was purified by column chromatog-
raphy on silica gel using 30/1 (v/v) petroleum ether/
dichloromethane as eluent. Pure compound was obtained as
a yellow powder (1.8 g, 83%).
(E)-4-(4-(benzo[d]thiazol-2-yl)styryl)-N,N-bis(4-bromophe-
nyl)aniline (M2)
Compound 5 (0.5 g, 1.39 mmol) and compound 6 (0.66 g,
1.53 mmol) were dissolved in 20 mL of anhydrous DMF
under nitrogen. To this solution was added NaH (0.15 g, 6.25
mmol) in an ice-water bath. Then the reaction was stirred
for 5 h at room temperature under nitrogen. After the reac-
tion, the mixture was poured into water. The precipitate was
filtered and washed with water and methanol. The crude
product was purified by column chromatography (PE/CHCl3,
2:1) to give 0.62 g of M2.
1
Yield: 70%. H NMR (CDCl3, 300 MHz) d (ppm): 8.08 (d, J ¼
1H NMR (CDCl3, 300 MHz) d (ppm): 7.98 (s, 2H), 7.83 (s,
2H), 7.04 (s, 2H), 2.69 (t, J ¼ 7.5 Hz, 4H), 1.72–1.68 (m, 4H),
8.1 Hz, 3H), 7.92 (d, J ¼ 7.8 Hz, 1H), 7.61 (d, J ¼ 8.1 Hz,
2H), 7.51 (t, J ¼ 7.2 Hz, 1H), 7.45–7.36 (m, 7H), 7.18 (d, J ¼
3854
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
16.2 Hz, 1H), 7.08–6.97 (m, 7H). 13C NMR (CDCl3, 150 MHz)
d (ppm): 167.86, 154.45, 146.93, 146.37, 140.35, 135.23,
132.71, 132.65, 132.28, 129.75, 128.13, 128.07, 127.07,
126.87, 126.59, 126.05, 125.39, 124.13, 123.37, 121.83,
116.23. Anal. Calcd for C33H22Br2N2S (%): C, 62.08; H, 3.47;
N, 4.39. Found: C, 61.65; H, 3.28; N, 4.27. EI-MS: m/z 638.0
(Calcd: 638.0).
ble portion was collected, concentrated, and precipitated
from methanol to yield P1 as a red solid.
Yield: 80%. 1H NMR (CDCl3, 300 MHz) d (ppm): 8.12–8.08
(m, 5H), 7.91 (br, 3H), 7.78 (br, 4H), 7.65–7.60 (m, 9H),
7.51–7.48 (m, 8H), 7.42–7.37 (m, 2H), 7.31–7.20 (m, 6H),
7.11–7.05 (m, 1H), 2.81 (br, 4H), 2.06 (br, 8H), 1.77 (br, 8H),
1.26 (br, 28H), 1.10 (br, 28H), 0.88–0.85 (m, 6H), 0.79–0.77
(m, 20H).
(E)-2-(4-(2-(2,5-dibromothiophen-3-yl)vinyl)phenyl)
benzo[d]thiazole (M3)
Synthesis of P2
M3 was obtained with a procedure similar to that for M2,
excepted with the use of 2,5-dibromothiophene-3-carbalde-
hyde (7; 0.38 g, 1.39 mmol) as one reactant. The crude prod-
uct was purified by column chromatography (PE/CHCl3, 1:1)
to give 0.5 g of M3.
P2 was obtained with a procedure similar to that for P1,
except with the use of M3 (0.078 g, 0.164 mmol) instead of
M2.
Yield: 85%. 1H NMR (CDCl3, 300 MHz) d (ppm): 8.08 (br,
5H), 7.91–7.70 (m, 9H), 7.60–7.54 (m, 9H), 7.40 (br, 2H),
7.26 (m, 2H), 2.82 (br, 4H), 2.09 (br, 8H), 1.76 (br, 4H),
1.26–1.13 (m, 60H), 0.88–0.80 (m, 26H).
Yield: 75% 1H NMR (CDCl3, 300 MHz) d (ppm): 8.10–8.07
(m, 3H), 7.92 (d, J ¼ 7.8 Hz, 1H), 7.61 (d, J ¼ 8.4 Hz, 2H),
7.51 (t, J ¼ 7.5 Hz, 1H), 7.40 (t, J ¼ 7.8 Hz, 1H), 7.26 (d, J ¼
3.3 Hz, 1H), 7.11 (d, J ¼ 16.2 Hz, 1H), 6.94 (d, J ¼ 16.2 Hz,
1H). 13C NMR (CDCl3, 150 MHz) d (ppm): 139.79, 131.72,
131.46, 131.14, 131.09, 128.68, 128.44, 128.07, 127.80,
127.65, 126.31, 125.72, 125.44, 125.37, 125.26, 125.09,
123.80, 122.97, 122.89, 112.26, 110.66. Anal. Calcd for
Synthesis of P3
P3 was obtained with a procedure similar to that for P1,
except with the use of M4 (0.077 g, 0.164 mmol) instead of
M2.
Yield: 81%. 1H NMR (CDCl3, 300 MHz) d (ppm): 8.61 (br,
1H), 8.22 (br, 5H), 8.06–7.97 (m, 7H), 7.91–7.82 (m, 7H),
7.65–7.54 (m, 8H), 2.82 (br, 4H), 2.07 (br, 8H), 1.76 (br, 4H),
1.26–1.12 (m, 60H), 0.88–0.80 (m, 26H).
C19H11Br2NS2 (%): C, 47.82; H, 2.32; N, 2.93. Found: C,
48.09; H, 2.23; N, 3.04. EI-MS: m/z 477.0 (Calcd: 476.9).
(E)-2,5-dibromo-3-(2-(pyren-1-yl)vinyl)thiophene (M4)
M4 was obtained with a procedure similar to that for M2,
excepted with the use of diethyl(2,5-dibromothiophen-3-
yl)methylphosphonate (8; 1 g, 2.55 mmol) and pyrene-1-car-
baldehyde (9; 0.6 g, 2.61 mmol) as the reactant. The crude
product was purified by column chromatography (PE/CHCl3,
10:1) to give 0.83 g of M4.
Synthesis of P4
M6 (0.216 g, 0.244 mmol), M1 (0.098 g, 0.123mmol), M4
(0.057g, 0.122mmol), and Pd (PPh3)4 (2% mmol, 6 mg)
were dissolved in toluene (10 mL). The polymerization was
ꢃ
carried out at 110 C for 3 days under argon. After the reac-
tion was completed, the mixture was cooled to room temper-
ature, and the polymer was precipitated by slowly adding
the mixture into CH3OH (200 mL). The precipitated material
was collected by filtration through a funnel. Then, the crude
product was washed via a Soxhlet apparatus with methanol,
acetone, hexane, and finally extracted with chloroform. Only
the chloroform-soluble portion was collected, concentrated,
and precipitated from methanol to yield P4 as a black solid.
1
Yield: 70%. H NMR (CDCl3, 300 MHz) d (ppm): 8.41 (d, J ¼
9.3 Hz, 1H), 8.31 (d, J ¼ 8.4 Hz, 1H), 8.21–8.12 (m, 4H),
8.07–7.97 (m, 4H), 7.44 (s, 1H), 7.23 (d, J ¼ 15.6Hz, 1H). 13C
NMR (CDCl3, 75 MHz) d (ppm): 139.79, 131.72, 131.46,
131.14, 131.09, 128.68, 128.44, 128.07, 127.80, 127.65,
126.31, 125.72, 125.44, 125.37, 125.26, 125.09, 123.80,
122.97, 122.89, 112.26, 110.66. Anal. Calcd for C22H12Br2S
(%): C, 56.44; H, 2.58. Found: C, 56.31; H, 2.63. EI-MS: m/z
468.0 (Calcd: 467.9).
Yield: 85%. 1H NMR (CDCl3, 300 MHz) d (ppm): 8.00–7.26
(m, 20H), 4.31 (br, 8H), 2.95–0.87 (m, 142H).
RESULTS AND DISCUSSION
Polymer Synthesis
Synthesis of P1
Synthesis
M5 (0.192 g, 0.328 mmol), M1 (0.130 g, 0.164 mmol), M2
(0.104 g, 0.163 mmol), and Pd (PPh3)4 (2% mmol, 8 mg)
were dissolved in toluene (12 mL). A total of 6 mL aqueous
solution of Bu4NOH (10%) was then added to the reaction
mixture. The polymerization was carried out at 90 ꢃC for 3
days under argon. After the reaction was completed, the mix-
ture was cooled to room temperature, and the polymer was
precipitated by slowly adding the mixture into CH3OH (200
mL). The precipitated material was collected by filtration
through a funnel. Then, the crude product was washed via a
Soxhlet apparatus with methanol, acetone, hexane, and
finally extracted with chloroform. Only the chloroform-solu-
Monomer Synthesis
A long alkyl chain (dodecyl-) was added to the thiophene in
Compound 1 to keep good solubility of M1. As shown in
Scheme 1, Compound 3 was synthesized by Suzuki coupling
reaction in toluene and water using Pd(PPh3)4 as catalyst
and K2CO3 as base at 90 ꢃC for 48 h. M1 was obtained by
bromination of Compound 3 via NBS. Compound 5 was syn-
thesized by refluxing of the blend solution of Compound 4
and triethyl phosphite at 120 ꢃC for about 16 h. M2, M3,
and M4 were synthesize by Wittig–Hornor reaction using
NaH as base in DMF at room temperature overnight, and
these monomers were all trans-configuration verified by 1H
SYNTHESIS AND PROPERTIES OF 2D D-A COPOLYMERS, CHEN ET AL.
3855

JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 1 Synthetic Routes of Monomers M1–M4. Conditions: (a) Pd(PPh3)4, K2CO3, toluene/H2O, 90 ꢃC, 48 h; (b) NBS, CHCl3/
CH3COOH, rt, 12 h; (c) P(OEt)3, 120 ꢃC, 16 h; (d) NaH, DMF, rt, 12 h.
NMR with a split number of about 16 Hz of the hydrogen in
double bond.34
washed via a Soxhlet apparatus with methanol, acetone, hex-
ane, and finally chloroform. Only the chloroform-soluble por-
tion was collected to obtain a pure, high molecular weight,
solution processable polymer. The real segment ratios were
estimated from the 1H NMR spectra of the polymers and
were found to be agreed with the designed ratio very well
(Supporting Information, Fig. S1). All the polymers have
good solubility in common organic solvents such as toluene,
Polymer Synthesis
As shown in Scheme 2, Polymers P1, P2, and P3 were syn-
thesized by Suzuki coupling reaction, and P4 was prepared
by Stille coupling reaction. After the reaction was completed,
the crude polymers were precipitated from methanol and
3856
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
FIGURE 2 TGA plots of the copolymers with a heating rate of 10
ꢃC/min under inert atmosphere. [Color figure can be viewed in
the online issue, which is available at wileyonlinelibrary.com.]
Optical Properties
Figure 3 shows the normalized UV–vis absorption spectra of
the polymers in chloroform and in the solid films spin-
coated on quartz substrates. All the polymers showed two
main peaks: one at around 400 nm originating from the
SCHEME 2 Synthetic Routs of Polymers P1–P4. Conditions: (a)
Pd (PPh3)4, Bu4NOH (10%, aqueous), toluene, 90 ꢃC, 72 h; (b)
Pd(PPh3)4, toluene, 110 ꢃC, 72 h.
chloroform, THF, and chlorobenzene. A noticeable amount of
residue remained in the extraction thimble when P4 was
purified. This insoluble fraction maybe caused by the poorer
solubility of M6 compared with M5, which has a branched
alkyl chain. As a result, P4 has a relatively lower molecular
weight than the other copolymers. Molecular weights and
polydispersity indices (PDIs) of polymers, as shown in Table
1, are determined by gel permeation chromatography (GPC)
analysis in THF with a polystyrene standard calibration.
Thermal Stability
Thermal stability of the polymers was investigated with TGA,
as shown in Figure 2. The TGA plots reveals that there were
two degradation stages for P1 and P2, one around 190 ꢃC
where the polymers began to lose weight and one around
400 ꢃC where the weight-loss reached 5%. It may be more
appropriate to denote the first temperature as the decompo-
sition temperature (Td) of P1 and P2, and the Td of P3 and
ꢃ
P4 were 418 and 448 C, respectively, which were the onset
temperatures of 5% weight-loss. All the decomposition tem-
peratures are high enough for device fabrication process.
TABLE 1 Molecular Weights and Thermal Property of the
Polymers
PDIa (Mw/Mn)
Td (ꢃC)
a
a
Polymers
Mn
Mw
P1
P2
P3
P4
a
21.8K
37.8K
29.0K
9.76K
55.4K
89.6K
68.9K
29.7K
2.5
2.4
2.4
3.0
190b
190b
418c
448c
Mn, Mw, and PDI of the polymers were determined by GPC using poly-
FIGURE 3 UV–vis spectra of all polymers: (a) in chloroform so-
lution and (b) in solid film. [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.com.]
styrene standards in THF.
b
Temperatures at which the polymers began to lose weight.
c
The 5% weight-loss temperatures under N2 atmosphere.
SYNTHESIS AND PROPERTIES OF 2D D-A COPOLYMERS, CHEN ET AL.
3857

JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
mers with absorption range from 300 nm to about 742 nm
in the film, from which an optical energy band gap was cal-
culated to be as low as 1.67 eV, and the absorption intensity
in the long wavelength is as strong as that in the short wave-
length, indicating that a more effective absorption of sunlight
can be realized to compare the other three polymers. On the
whole, the introduction of side chains could increase the
absorption intensity in the short wavelength range.
Electrochemical Properties
Electrochemical cyclic voltammetry is often used to measure
the redox properties of the polymers from which the energy
levels of HOMO and LUMO can be estimated. Figure 4 shows
the cyclic voltammograms of the four polymer films on Pt disk
electrode in 0.1 mol/L Bu4NPF6 acetonitrile solution. The
HOMO and LUMO energy levels of polymers were calculated
from the onset oxidation potentials (Eoonxset) and onset reduction
potentials (Eroendset), respectively, according to eqs 1 and 2.35–37
The electrochemically determined band gaps were deduced
from the difference between onset potentials from oxidation
and reduction of copolymers as depicted in eq 3.35–37
FIGURE 4 Cyclic voltammograms of P1–P4 films on a platinum
electrode measured in 0.1 mol/L Bu4NPF6 acetonitrile solutions
at a scan rate of 100 mV/s. [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.com.]
ox
HOMO ¼ ꢁeðE
LUMO ¼ ꢁeðE
þ 4:8ÞðeVÞ
(1)
(2)
(3)
onset
p–p* transition and the absorption of side chain groups, and
the longer wavelength absorption should be due to an ICT
interaction between the donors and acceptors along the
main chain. The ICT interactions in electron rich–poor alter-
nating structures can reduce the band gap of polymers. In
the film, the spectra were somewhat broad and slightly red-
shifted in the longer wavelength region, 13–15 nm for P1–
P3, and 21 nm for P4, relative to those in solution. From the
relative absorption intensity, we can see that the short wave-
length absorption intensity is much stronger than that in the
long wavelength for P1–P3, and the absorption spectra are
quite similar. It indicates that in our cases the effects of the
side chain groups to the UV–vis absorption are almost the
same no matter the moieties are electron-deficient benzo-
thiazole unit or electron-rich pyrene unit when the main
chains are constructed by the same donor and acceptor, and
the connection units also affect little to the absorption spec-
tra, compared P1 with P2, which have triphenylamine and
thiophene moiety as the connection site, respectively. P4
exhibited the best absorption spectra among the four poly-
red
onset
þ 4:8ÞðeVÞ
ox
red
onset
Egec ¼ eðE
ꢁ E
ÞðeVÞ
onset
The electrochemical data of all the polymers are summarized
in Table 2. The Eegc values of polymers are slightly higher
than the corresponding optical band gaps, which is probably
due to the exciton binding energy of polymers.38 The electro-
chemical data shows that there is little influence on the elec-
trochemical properties among P1, P2, and P3, when the side
chain groups are altered with the main chain donor–acceptor
units unchanged. However, when the donor moiety was
changed from fluorene to benzodithiophene (BDT), both the
HOMO and LUMO levels were altered. It indicates that the
groups along the backbone contribute more to the electro-
chemical properties of polymers in our cases.
The offsets between the LUMO levels of all polymers and PCBM
(ꢁ3.91 eV)39 is larger than 0.3 eV, indicating that the charge
transfer from the polymers to PCBM would be efficient.40 As
TABLE 2 Optical and Electrochemical Data of All Polymers
UV–Vis Absorption
CHCl3 Solutiona
Filmb
Cyclic Voltammetry
ox
red
konset
konset
E
E
onset
onset
Polymer
kmax (nm)
(nm)
Eg (eV)c
kmax (nm)
(nm)
Eg (eV)c
(V)/HOMO (eV)
(V)/LUMO (eV)
P1
P2
P3
P4
a
382
377
382
414
504
504
504
523
589
589
591
723
2.11
2.11
2.10
1.72
386
374
388
422
517
519
517
544
603
612
609
743
2.06
2.03
2.03
1.67
0.66/ꢁ5.46
0.62/ꢁ5.42
0.64/ꢁ5.44
0.35/ꢁ5.15
ꢁ2.09/ꢁ2.71
ꢁ2.02/ꢁ2.78
ꢁ2.08/ꢁ2.72
ꢁ1.80/ꢁ3.00
Measured in chloroform solution.
Cast from chloroform solution.
b
c
Band gap estimated from the onset wavelength (kedge) of the optical absorption: Eg ¼ 1240/kedge
.
3858
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
FIGURE 6 J–V characteristics of photovoltaic devices with an
active layer of the polymers:PCBM (weight ratio ¼ 1:3) mixture.
[Color figure can be viewed in the online issue, which is avail-
able at wileyonlinelibrary.com.]
As shown in Figure 5, the HOMO energy levels are nearly
delocalized over the whole molecules for P3 and P4, but
partly delocalized to the side chains for P1 and P2, which
are due to the electron deficiency of benzothiazole unit at
the end of the side chains. On the other side, the delocaliza-
tion of HOMO levels demonstrates that the side chain groups
are conjugated to the main chains very well and changing
the segment ratios will alter the HOMO levels of polymers.
The LUMO energy levels are all predominantly localized on
the benzothiadiazole (BTZ) units, so the alternation of seg-
ment ratios will not affect the LUMO levels a lot. These
results implied that the HOMO–LUMO transition for the four
polymers is mainly accompanied by charge transfer from the
electron-rich segments to BTZ units due to the strong elec-
tron deficiency of BTZ units. The HOMO and LUMO levels of
the molecules from the calculation are listed in Table 3.
When compared with the first three polymers, the LUMO
level of P4 is lowered by about 0.17 eV, which shows that
the conjugation of P4 is better than the others. When com-
pare with the data from CV measurement, it shows that the
tendencies of the data change on HOMO or LUMO level from
the calculation are almost the same.
FIGURE 5 HOMO and LUMO wavefunctions of the four
oligomer (n ¼ 1) model systems calculated at the B3LYP/6-
31g(d) level. [Color figure can be viewed in the online issue,
which is available at wileyonlinelibrary.com.]
the open-circuit voltage (Voc) of PSCs is related to the difference
between the LUMO level of the electron acceptor (PCBM) and
the HOMO level of the electron donor (polymer),41 the previous
three polymers (P1–P3) would lead to a higher Voc than P4,
owing to the more electron-rich BDT unit introduced to the
backbone of P4. Furthermore, the HOMO energy levels of all
polymers are well aligned with the workfunction of the
PEDOT:PSS (ꢁ5.0 eV),19 indicating that holes can be easily
transported from the HOMO of polymers to PEDOT:PSS. There-
fore, all the polymers can be used as electron donors with
PCBM as an electron acceptor for BHJ devices.
Molecular Orbital Calculations
The geometries of oligomer structures of the four copoly-
mers were optimized at the density functional theory (DFT)
ri-BP86/def2-SVP level, then the electronic properties were
calculated at B3LYP/6-31g(d) level.42,43 The Frontier energy
levels (HOMO and LUMO) were characterized for the neutral
electronic states. Note that the calculations were performed
on model systems of copolymers where all alkyl chain sub-
stituents were replaced with methyl groups (this has only
minimal effect on the electronic properties).
Hole Mobility
Hole mobility is another important parameter for the poly-
mer applied to PSC devices, because high hole mobility is
essential for efficient charge extraction and a good fill factor
(FF). Here, we measured the hole mobility of the copolymers
TABLE 4 Photovoltaic Performances of the PSCs Based on
P1–P4:PCBM (1:3 w/w) under the Illumination of AM 1.5,
100 mA/cm2
TABLE 3 B3LYP/6-31G(d) Gas-Phase HOMO and LUMO Levels
of the Oligomer (n 5 1) Calculations
Compound
HOMO (eV)
LUMO (eV)
Eg (eV)
Active Layer
Voc (V)
Jsc (mA/cm2)
FF (%)
PCE (%)
P1
P2
P3
P4
ꢁ5.16
ꢁ5.08
ꢁ5.02
ꢁ4.85
ꢁ2.62
ꢁ2.64
ꢁ2.63
ꢁ2.80
2.54
2.44
2.39
2.05
P1:PCBM ¼ 1:3
P2:PCBM ¼ 1:3
P3:PCBM ¼ 1:3
P4:PCBM ¼ 1:3
0.62
0.75
0.90
0.79
2.79
1.03
1.52
1.64
32.2
33.5
31.7
58.6
0.56
0.26
0.43
0.76
SYNTHESIS AND PROPERTIES OF 2D D-A COPOLYMERS, CHEN ET AL.
3859

JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 7 AFM height images for P1–P4:PCBM (1:3 w/w). All images are 1 lm ꢀ 1 lm.
by space-charge limit current (SCLC) method using a device
structure of ITO/PEDOT:PSS/polymer/Au. For the hole-only
devices, SCLC is described by
Photovoltaic Properties
Bulk heterojunction photovoltaic devices were constructed
to investigate and compare the photovoltaic properties of
the four polymers. To maintain similarly structured devices,
all polymers were blended with PCBM at 1:3 weight ratio in
chlorobenzene at 30 mg/mL and identical spin rate (3000
rpm) was used. A typical fabricated solar cell has a configu-
ration of ITO/PEDTO:PSS/polymer:PCBM (1:3 w/w)/Al. The
current–voltage characteristics of the solar cells based on
these four polymers blended with PCBM are shown in Figure
6 under the illumination of AM 1.5, 100 mW/cm2. The corre-
sponding open-circuit voltage (Voc), short-circuit current (Jsc),
FF, and PCE of the devices are summarized in Table 4.
pffiffiffiffiffiffiffiffiffiffiffiffiffi
J ffi ð9=8Þee0l0V2expð0:89 V=E0LÞ=L3
(4)
where e is the dielectric constant of the polymer, e0 is the
permittivity of the vacuum, l0 is the zero-field mobility, E0 is
the characteristic field, J is the current density, L is the thick-
ness of the blended films layer, V ¼ Vappl ꢁ Vbi, Vappl is the
applied potential, and Vbi is the built-in potential, which
results from the difference in the work function of the anode
and the cathode (in this device structure, Vbi ¼ 0.2 V). The
results are plotted as ln(JL3/V2) versus (V/L)0.5 44–46
Accord-
.
ing to eq 4, the hole mobility obtained are 5.33 ꢀ 10ꢁ4, 3.23
ꢀ 10ꢁ6, 1.77 ꢀ 10ꢁ4, and 1.82 ꢀ 10ꢁ3 cm2/V s for P1–P4,
respectively. Obviously, the hole mobility of P4 is in the
same scale as that of P3HT (10ꢁ3 cm2/V s), and it is fit for
the application as photovoltaic donor materials in PSCs. As
reported in literature,47 the polymers with similar backbone
structure compared with P4 (but without a pendent conju-
gated group), showed the hole mobility in the scale of 10ꢁ5
cm2/V s, which is almost two orders of magnitude smaller
than that of P4. So, the introduction of a pendent conjugated
groups to polymers can increase the hole mobility.
The PSCs based on P3 shows the highest Voc, benefited from
the rather low HOMO energy level. Although the HOMO level
of P1 and P2 are almost the same as that of P3, they show a
little lower value of Voc, 0.62 and 0.75 V, respectively. The
Voc is proportional to the offset between HOMO level of do-
nor (polymer) and LUMO level of acceptor (i.e., PCBM). How-
ever, we are surprised to find that the Voc of the PSC based
on P4 with a higher HOMO level is larger than those of PSCs
based on P1 and P2. On the whole, all the devices exhibit
relatively high Voc, with a best one as high as 0.9 V. The FF
of the PSC based on P4 is fair enough with a value of 58.6%,
3860
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
eV, which is an ideal value for donor materials blended with
PCBM for application on PSCs. The electrochemical data of
P1, P2, and P3 also indicated that these copolymers are suit-
able as electron donors with PCBM as the acceptor for BHJ
PSCs. The hole mobility were measured with SCLC method
with high value of 1.82ꢀ10ꢁ3 cm2/VÁs for P4, and moderate
value for P1 and P3, which indicate that 2D conjugated poly-
mers can facilitate the hole transportation. PSC devices
based on the polymers blended with PCBM with a ratio of
1:3 in weight showed a high Voc of 0.9 eV for P3 and good
FF of 58.6 % for P4. The PCE of all the devices were not
very high due to the low Jsc, which may owe to the bad film
morphology. However,
a lot of improvements may be
achieved by various approaches, such as changing the ratio
of polymers:PCBM and adding some additive to the solvent
in film processing to improve the film morphology. In gen-
eral, 2D conjugated copolymers with different pendent
groups can lead to some positive effect on their photovoltaic
properties.
FIGURE 8 IPCE of the PSC based on P4:PCBM (1:3 w/w).
ascribed to the best hole mobility among all the polymers.
Also, the FF of the PSCs based on the other three polymers
are not bad with the value around 32%. The PCE of the poly-
mers are below 1%, which is mainly due to the low Jsc value
that depends on many factors such as the morphology of the
blend films. Thus, the film morphology of polymer:PCBM
blends was studied. As the tapping-mode atomic force mi-
croscopy (AFM) images shown in Figure 7, the surface of the
active layers of polymers/PCBM is relatively rough, with a
root-mean-square roughness (rms) of 3.68, 2.77, 11.9, and
6.33 nm for P1–P4, respectively. However, the phase separa-
tion between the polymer and PCBM is not clear, and the do-
main size is relatively large, which may lead to low Jsc and
PCE.
This work was financially supported by the National Science
Foundation of China (No. 20772094, 20874106). The authors
thank Q. Luo for AFM measurements.
REFERENCES AND NOTES
1 Dennler, G.; Scharber, M. C.; Brabec, C. J. Adv Mater 2009,
21, 1323–1338.
2 Helgesen, M.; Sondergaard, R.; Krebs, F. C. J Mater Chem
2010, 20, 36–60.
3 Chen, Y.-J.; Yang, S.-H.; Hsu, C.-S. Chem Rev 2009, 109,
5868–5923.
The incident photon-to-converted current efficiency (IPCE)
of the PSC device based on P4/PCBM was further tested in
considering the better photovoltaic performance of P4. It is
apparent that the device exhibited a broad response range,
covering from 300 to 700 nm, as shown in Figure 8. In com-
parison of the IPCE curve with the absorption spectrum of
P4, the photon-to-electron conversion efficiency correspond-
ing to the longer wavelength absorption peak (at ca. 600
nm) of P4 is quite low, indicating that the ICT absorption of
the 2D D-A copolymer contributes to the photovoltaic con-
version much less than that of the p–p* absorption in the
shorter wavelength region of 400ꢂ500 nm.
4 Li, Y.; Zou, Y. Adv Mater 2008, 20, 2952–2958.
5 Li, G.; Shrotriya, V.; Huang, J. S.; Yao, Y.; Moriarty, T.; Em-
ery, K.; Yang, Y. Nat Mater 2005, 4, 864–868.
6 Halls, J. J. M.; Walsh, C. A.; Greenham, N. C.; Marseglia, E.
A.; Friend, R. H.; Moratti, S. C.; Holmes, A. B. Nature 1995, 376,
498–500.
7 Xin, H.; Kim, F. S.; Jenekhe, S. A. J Am Chem Soc 2008, 130,
5424–5425.
8 van Bavel, S. S.; Sourty, E.; de With, G.; Loos, J. Nano Lett
2009, 9, 507–513.
9 Yu, G.; Gao, J.; Hummelen, J. C.; Wudl, F.; Heeger, A. J. Sci-
CONCLUSIONS
ence 1995, 270, 1789–1791.
We have successfully synthesized a series of new 2D conju-
gated copolymers with donors–acceptors in main chains and
pendent electron-rich or -deficient groups. Along the main
chains of the polymers, fluorene, triphenylamine, thiophene,
and benzodithiophene were designed as donor units with
benzothiadiazole as the acceptor unit. They showed good
solubility in common organic solvents, good thermal stability,
and high molecular weights. Their absorption spectra were
tested, and P4 exhibited the widest absorption range from
300 to 724 nm in chloroform and to 743 nm in solid film.
The optical energy band gap of P4 was estimated to be 1.67
10 Ma, W.; Yang, C.; Heeger, A. J. Adv Funct Mater 2005, 15,
1617–1622.
11 Li, G.; Shrotriya, V.; Yao, Y.; Huang, J.; Yang, Y. J Mater
Chem 2007, 17, 3126–3140.
12 Liang, Y.; Xu, Z.; Xia, J.; Tsai, S.-T.; Wu, Y.; Li, G.; Ray, C.;
Yu, L. Adv Mater 2010, 22, E135–E138.
13 Chen, H.; Hou, J.; Zhang, S.; Liang, Y.; Yang, G.; Yang, Y.;
Yu, L.; Wu, Y.; Li, G. Nat Photonics 2009, 3, 649–653.
14 Muhlbacher, D.; Scharber, M.; Morana, M.; Zhu, Z.; Waller,
¨
D.; Gaudiana, R.; Brabec, C. Adv Mater 2006, 18, 2884–2889.
SYNTHESIS AND PROPERTIES OF 2D D-A COPOLYMERS, CHEN ET AL.
3861

JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
15 Blouin, N.; Michaud, A.; Gendron, D.; Wakim, S.; Blair, E.;
Neagu-Plesu, R.; Belletete, M.; Durocher, G.; Tao, Y.; Leclerc,
M. J Am Chem Soc 2008, 130, 732–742.
34 Silverstein, R. M.; Webster, F. X.; Kiemle, D. J. Spectromet-
ric Identification of Organic Compounds, 7th ed.; Wiley: Amer-
ica, 2005; Chapter 3, pp 198.
16 Zhang, M.; Fan, H.; Guo, X.; He, Y.; Zhang, Z.; Min, J.;
Zhang, J.; Zhao, G.; Zhan, Z.; Li, Y. Macromolecules 2010, 43,
8714–8717.
35 Bredas, J. L.; Silbey, R.; Boudreaux, D. S.; Chance, R. R. J
Am Chem Soc 1983, 105, 6555–6559.
36 De Leeuw, D. W.; Simenon, M. M. J.; Brown, A. R.; Einer-
17 Wang, E.; Hou, L.; Wang, Z.; Hellstrom, S.; Mammo, W.;
hand, R. E. F. Synth Met 1997, 87, 53–59.
¨
Zhang, F.; Inganas, O.; Andersson, M. R. Org Lett 2010, 12,
¨
37 Pommerehne, J.; Vestweber, H.; Guss, W.; Mahrt, R. F.;
4470–4473.
Bssler, H.; Porsch, M.; Daub, J. Adv Mater 1995, 7, 551–554.
18 Zhou, H.; Yang, L.; Xiao, S.; Liu, S.; You, W. Macromole-
38 Alvarado, S. F.; Seidler, P. F.; Lidzey, D. G.; Bradley, D. D.
cules 2010, 43, 811–820.
C.; Phys Rev Lett 1998, 81, 1082–1085.
19 Park, S. H.; Roy, A.; Beaupre´, S.; Cho, S.; Coates, N.; Moon,
J. S.; Moses, D.; Leclerc, M.; Lee, K.; Heeger, A. J. Nat Pho-
tonics 2009, 3, 297–303.
39 He, Y.; Li, Y. Phys Chem Chem Phys 2011, 13, 1970–1983.
40 Mihailetchi, V. D.; Duren, J. K. J. V.; Blom, P. W. M.; Hummelen,
J. C.; Janssen, R. A. J.; Kroon, J. M.; Rispens, M. T.; Verhees, W. J.
H.; Wienk, M. M. Adv Funct Mater 2003, 13, 43–46.
20 Beaujuge, P. M.; Pisula, W.; Tsao, H. N.; Ellinger, S.; Mullen,
¨
K.; Reynolds, J. R. J Am Chem Soc 2009, 131, 7514–7515.
41 Scharber, M. C.; Muhlbacher, D.; Koppe, M.; Denk, P.; Wal-
¨
21 Hou, J.; Chen, T. L.; Zhang, S.; Chen, H.; Yang, Y. J Phys
dauf, C.; Heeger, A. J.; Brabec, C. J. Adv Mater 2006, 18, 789–794.
Chem C 2009, 113, 1601–1605.
¨
42 Eichkorn, K.; Treutler, O.; Ohm, H.; Haser, M.; Ahlrichs, R.
¨
22 Huang, F.; Chen, K.-S.; Yip, H.-L.; Hau, S. K.; Acton, O.;
Zhang, Y.; Luo, J.; Jen, A. K.-Y. J Am Chem Soc 2009, 131,
13886–13887.
Chem Phys Lett 1995, 242, 652–660.
43 Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Men-
nucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.;
Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnen-
berg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hase-
gawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.; Vreven, T.; Montgomery, J. A.; Peralta, J. E.; Ogliaro, F.;
Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov,
V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell,
A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.;
Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.;
Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J.
W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.;
Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.;
Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D.
J. GAUSSIAN 09 (Revision A.02); Gaussian, Inc.: Wallingford,
CT, 2009.
23 Hou, J.; Tan, Z.; Yan, Y.; He, Y.; Yang, C.; Li, Y. J Am Chem
Soc 2006, 128, 4911–4916.
24 Zhou, E.; Tan, Z.; Yang, Y.; Huo, L.; Zou, Y.; Yang, C.; Li, Y.
Macromolecules 2007, 40, 1831–1837.
25 Duan, C.; Chen, K.; Huang, F.; Yip, H.; Liu, S.; Zhang, J.;
Jen, A. K. -Y.; Cao, Y. Chem Mater 2010, 22, 6444–6452.
26 Fan, H. J.; Zhang, Z. G.; Li, Y. F.; Zhan, X. W. J Polym Sci A:
Polym Chem 2011, 49, 1462–1470.
27 Kong, H.; Chung, D. S.; Kang, I.; Park, J.; Park, M.; Jung, I.
H.; Park, C. E.; Shim, H. J Mater Chem 2009, 19, 3490–3499.
28 Wu, C.; Lu, M.; Tsai, P. Macromol Chem Phys 2009, 210,
1851–1855.
29 Yoshino, K.; Kohno, T.; Uno, T.; Morita, T.; Tsukamoto, G. J
Med Chem 1986, 29, 820–825.
30 Seok, J. H.; Park, S. H.; EI-Khouly, M. E.; Araki, Y.; Ito, O.;
44 Chirvase, D.; Chiguvare, Z.; Knipper, M.; Parisi, J.; Dyako-
Kay, K. J Orgamet Chem 2009, 694, 1818–1825.
nov, V.; Hummelen, J. C. Phys Rev B 2004, 70, 235207–235213.
31 Mori, H.; Takano, K.; Endo, T. Macromolecules 2009, 42,
45 Malliaras, G. G.; Salem, J. R.; Brock, P. J.; Scott, C. Phys
7342–7352.
Rev B 1998, 58, 13411–13414.
32 Lu, K.; Sun, X.; Liu, Y.; Di, C.; Xi, H.; Yu, G.; Gao, X.; Du, C.
46 Martens, H. C. F.; Brom, H. B.; Blom, P. W. M. Phys Rev B
J Polym Sci Part A: Polym Chem 2009, 47, 1381–1392.
1999, 60, 8489–8492.
33 Li, Q.; Zou, J.; Chen, J.; Liu, Z.; Qin, J.; Li, Z.; Cao, Y. J Phys
47 Price, S. C.; Stuart, A. C.; You, W. Macromolecules 2010, 43,
Chem B 2009, 113, 5816–5822.
4609–4612.
3862
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA