Synthesis and photovoltaic properties of donor-acceptor copolymers based on 5,8-dithien-2-yl-2,3-diphenylquinoxaline

Article abstract of DOI:10.1021/cm101677x

Four donor-acceptor (D-A) type copolymers, namely, poly{9,9- dioctylfluorene-2,7-diyl-alt-5,8-dithien-2-yl-2,3-diphenylquinoxaline-5′, 5″-diyl} (PF-DTQx), poly{N-[1-(2′-ethylhexyl)-3-ethylheptanyl] carbazole-2,7-diyl-alt-5,8-dithien-2-yl-2,3-diphenylquinoxaline-5′, 5″-diyl} (PC-DTQx), poly{5,11-di(1-decylundecyl)indolo[3,2-b]carbazole-3, 9-diyl-alt-5,8-dithien-2-yl-2,3-diphenylquinoxaline-5′,5″-diyl} (PIC-DTQx), and poly{N-[1-(2′-ethylhexyl)-3-ethylheptanyl]-dithieno[3,2-b: 2′,3′-d]pyrrole-2,6-diyl-alt-5,8-dithien-2-yl-2,3- diphenylquinoxaline-5′,5″-diyl} (PDTP-DTQx), were synthesized by Suzuki or Stille coupling reactions. By changing the donor segment, the band gaps and energy levels of these 5,8-dithien-2-yl-2,3-diphenylquinoxaline (DTQx)-based polymers could be finely tuned. PDTP-DTQx exhibited the narrowest band gap of 1.56 eV and the absorption edge extended to 770 nm. We investigated bulk heterojunction type polymer solar cells (PSCs) based on these copolymers as the electron donor materials, and [6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM) or [6,6]-phenyl C₇₁ butyric acid methyl ester (PC₇₀BM) as the acceptor. The power conversion efficiency (PCE) of the PSCs was in the range of 1.17-3.23% under AM 1.5 illumination (100 mW/cm²).

Full text of DOI:10.1021/cm101677x

4890 Chem. Mater. 2010, 22, 4890–4895
DOI:10.1021/cm101677x
Synthesis and Photovoltaic Properties of Donor-Acceptor Copolymers
Based on 5,8-Dithien-2-yl-2,3-diphenylquinoxaline
Erjun Zhou,† Junzi Cong,† Keisuke Tajima,† and Kazuhito Hashimoto*,†,‡
†HASHIMOTO Light Energy Conversion Project, ERATO, Japan Science and Technology Agency (JST),
and ‡Department of Applied Chemistry, School of Engineering, The University of Tokyo, 7-3-1 Hongo,
Bunkyo-ku, Tokyo 113-8656, Japan
Received June 16, 2010. Revised Manuscript Received July 22, 2010
Four donor-acceptor (D-A) type copolymers, namely, poly{9,9-dioctylfluorene-2,7-diyl-alt-
5,8-dithien-2-yl-2,3-diphenylquinoxaline-50,500-diyl} (PF-DTQx), poly{N-[1-(20-ethylhexyl)-3-ethyl-
heptanyl]carbazole-2,7-diyl-alt-5,8-dithien-2-yl-2,3-diphenylquinoxaline-50,500-diyl} (PC-DTQx),
poly{5,11-di(1-decylundecyl)indolo[3,2-b]carbazole-3,9-diyl-alt-5,8-dithien-2-yl-2,3-diphenylquino-
xaline-50,500-diyl} (PIC-DTQx), and poly{N-[1-(20-ethylhexyl)-3-ethylheptanyl]-dithieno[3,2-b:20,30-d]-
pyrrole-2,6-diyl-alt-5,8-dithien-2-yl-2,3-diphenylquinoxaline-50,500-diyl} (PDTP-DTQx), were synthe-
sized by Suzuki or Stille coupling reactions. By changing the donor segment, the band gaps and energy
levels of these 5,8-dithien-2-yl-2,3-diphenylquinoxaline (DTQx)-based polymers could be finely tuned.
PDTP-DTQx exhibitedthe narrowestband gap of 1.56eVand the absorption edgeextended to770 nm.
We investigated bulk heterojunction type polymer solar cells (PSCs) based on these copolymers as the
electron donor materials, and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) or [6,6]-phenyl C71
butyric acid methyl ester (PC70BM) asthe acceptor. The power conversion efficiency(PCE) ofthe PSCs
was in the range of 1.17-3.23% under AM 1.5 illumination (100 mW/cm2).
Introduction
realizing highly efficient PSCs in terms of spectral matching
to the solar spectrum and charge separation efficiency at
the material interfaces. Thus, many novel conjugated poly-
mers have been synthesized relying on this strategy and
used in PSCs to reach power conversion efficiency (PCE)
of >6%.3
Among the wide variety of acceptor segments, 4,7-
dithien-2-yl-2,1,3-benzothiadiazole (DTBT) has been co-
polymerized with almost all available donor segments
including pyrrole,4 didecyloxyphenylene,5 fluorene,6 carba-
zole,7 silafluorene (or dibenzosilole),8 indeno[2,1-a]indene,9
cyclopenta[2,1-b:3,4-b]dithiophene,10 dithienosilole,11
dithieno[3,2-b:20,30-d]pyrrole,12 indolo[3,2-b]carbazole,13
Donor-acceptor (D-A) type alternating copolymers
with an electron-rich unit (donor) and an electron-deficient
unit (acceptor) in the polymer backbone have recently
drawn much attention for application to many opto-
electronic devices such as polymer light-emitting diodes
(PLEDs), field-effect transistors (FETs), sensors, photode-
tectors, and polymer solar cells (PSCs).1 This D-A ap-
proach for designing the polymers is highly effective for
tuning physical properties such as solubility, band gap,
energy levels, and carrier mobility by choosing a suitable
combination from the vast variety of donor and acceptor
segments available.2 These physical properties, especially
the absorption spectra and the energy levels, are critical for
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2010 American Chemical Society
pubs.acs.org/cm
Published on Web 08/03/2010

Article
Chem. Mater., Vol. 22, No. 17, 2010 4891
Scheme 1. Synthetic Route for the Monomer
benzo[2,1-b:3,4-b0]dithiophene,14 benzo[1,2-b:4,5-b0]dithio-
phene,15 indeno[1,2b]fluorene,16 ladder-type oligo-p-phenyl-
ene,17 and germafluorene.18 When these materials were
applied to PSCs, PCEs in the range of 0.41-6.1% were
achieved. Because PSC performance strongly depends on
the choice of the donor segment, the development of novel
and versatile building blocks such as DTBT and systematic
investigation of D-A type polymers are important areas
of research in the search for photovoltaic polymers with
superior properties.
copolymer of DTQx and fluorene, which has been re-
ported to give high photovoltaic performance,19f,g was
also synthesized for comparison. The structural simila-
rity of DTQx to DTBT provides similar versatility as a
building block for use in the coupling polymerization
reactions. The effects of the different donor segments on
the absorption spectra, energy levels and the photovoltaic
performance of the resulting DTQx-containing D-A
copolymers were investigated in detail.
Results and Discussion
Quinoxaline-based polymers have shown interesting
optoelectronic properties and considerable promise for
the design of D-A type photovoltaic polymers.19 In this
study, we investigate the combination of the 5,8-dithien-
2-yl-2,3-diphenylquinoxaline (DTQx) acceptor segment
with three well-known donor segments, namely, carba-
zole, indolo[3,2-b]carbazole, and dithieno[3,2-b:20,30-d]-
pyrrole. These three donor segments contain nitrogen
atoms, which have strong electron-donating ability. The
Material Synthesis. The monomer 3, 5,8-di(2-bromo-
thien-5-yl)-2,3-diphenylquinoxaline, was synthesized ac-
cording to a modified literature procedure,19a as shown in
Scheme 1. The synthetic routes for preparing the four
DTQ-based polymers are shown in Scheme 2. Three types
of DTQx-based copolymers, PF-DTQx, PC-DTQx, and
PIC-DTQx, were synthesized by the Suzuki coupling
reaction between 3 and the corresponding boronic esters
of the donor segments. PDTP-DTQx was synthesized by
the Stille coupling reaction between 3 and the bisstannyl
derivative of dithieno[3,2-b:20,30-d]pyrrole. For the syn-
thesis of PF-DTQx and PC-DTQx, the feed molar ratios
of the donor and the acceptor monomers was set to 100:95
to avoid the formation of a large insoluble fraction of the
polymers. As a result, all the polymers have good solubi-
lity in chloroform (CF), chlorobenzene (CB), and 1,2-
dichlorobenzene (DCB), and their number-average mo-
lecular weights (Mn) and the polydispersity indices were
in the range of 8.1-21.1 K and 1.4-1.9, respectively.
Optical and Electrochemical Properties. The normalized
UV-vis absorption spectra of the four copolymers in CHCl3
solutions are shown in Figure 1. The peak at the longer
wavelength can be attributed to intramolecular charge-trans-
fer (ICT) transitions. PF-DTQx, PC-DTQx, and PIC-DTQx
show similar absorption spectra with absorption maxima at
524, 517, and 514 nm, respectively. The slight blue shift for
PC-DTQx and PIC-DTQx, compared with PF-DTQx, is
likely because of the larger steric hindrance of the side chains
in these two polymers. In contrast, the absorption band of
PDTP-DTQx (617 nm) is at a considerably longer wave-
length compared with the absorptions bands of the other two
copolymers. This change in the absorption is similar to the
cases of DTBT-based copolymers; PF-DTBT, PC-DTBT
and PIC-DTBT have absorption maxima at 537, 545, and
531 nm, respectively,20 but the absorption peak of PDTP-
DTBT extends to 671 nm.12
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4892 Chem. Mater., Vol. 22, No. 17, 2010
Zhou et al.
Scheme 2. Synthetic Routes for the Four DTQx-Based Donor-Acceptor Type Copolymers
Figure 2. Normalized absorption spectra of the copolymer films on
quartz plates.
Figure 1. Normalized absorption spectra of the copolymers in CHCl3
solution.
segment. The optical band gaps (Eogpt) of the four poly-
mers are estimated from the absorption onset and sum-
marized in Table 1.
In addition to the absorption properties, the highest
occupied molecular orbital (HOMO) and lowest unoccu-
pied molecular orbital (LUMO) energy levels of the
conjugated polymers are key parameters that influence
The absorption spectra of the polymer films are shown
in Figure 2. The absorption maxima of the polymer films
are slighted red-shifted by 4-13 nm compared with those
of the polymer solutions, indicating that the intermole-
cular interaction in the solid state was restricted by the
large steric hindrance of both the alkyl chains in the donor
segments and the diphenyl group in the quinoxaline

Article
Chem. Mater., Vol. 22, No. 17, 2010 4893
Table 1. Optical and Electrochemical Properties of DTQx-Based Polymers
UV-vis absorption spectrum
cyclic voltammogram
in CHCl3
in film
p-doping
HOMO (eV)
n-doping
ox
red
(V)
on
polymer
λ
max (nm)
λmax (nm)
λ
onset (nm)
Eogpt (eV)
E
(V)
E
LUMO (eV)
EEg C (eV)
on
PF-DTQx
524
517
514
617
528
524
527
624
625
635
650
770
1.98
1.95
1.91
1.61
0.69
0.62
0.73
0.24
-5.49
-5.42
-5.53
-5.04
-1.37
-1.36
-1.26
-1.32
-3.43
-3.44
-3.54
-3.48
2.06
1.98
1.99
1.56
PC-DTQx
PIC-DTQx
PDTP-DTQx
Figure 4. I-V curves ofthe polymer solarcellsbasedonthe DTQx-based
Figure 3. Cyclic voltammograms of the polymers films deposited on a
platinum plate in an acetonitrile solution of 0.1 M [Bu4N]PF6 (Bu =
butyl) at a scan rate of 50 mV/s.
polymers under AM 1.5 illumination (100 mW/cm2).
where the active layer was composed of one of the DTQx-
based polymers as the donor and a fullerene derivative
(either PCBM or PC70BM) as the acceptor. The devices
were optimized by changing many conditions, such as the
ratio of the donor and the acceptor, the thickness of blend
films, the solvent, the thermal annealing temperature and
the cathode metal. For the polymer:PCBM systems, using
Al as the cathode and postdeposition annealing at 110 °C
for 5 min gave the best device performance. On the other
hand, the highest PCEs were achieved by using Ca/Al as
cathode and without postdeposition annealing for the
polymer:PC70BM systems.
Figure 4 shows the I-V curves of the optimized devices
based on each of the DTQx-based polymers under illu-
mination of AM 1.5 simulated solar light (100 mW/cm2).
The corresponding VOC, short-circuit current (ISC), fill
factor (FF), and PCE of the devices are summarized in
Table 2.
The device based on PF-DTQx:PCBM spin-coated
from CB had PCE of 1.75%. Use of the mixture solvent
of CB and CF (2:1 by volume) for the same component
increased the PCE to 2.78%. Use of PC70BM as acceptor
further improved the efficiency to 3.23%. This large
enhancement of the photovoltaic performance could
be attributed to the change in the morphology of the
blend film.19g Atomic force microscopy (AFM) images
(Figure 5) clearly show large domains with a size of ∼100
nm in the blend films prepared from CB. This would
diminish exciton migration to the donor/acceptor inter-
face and would be unfavorable for charge separation. The
morphology of the blend films of both PF-DTQx:PCBM
the overall performance of the photovoltaic device through
the efficiency of charge separation and the open-circuit
voltage (VOC). Cyclic voltammetry (CV) was used to deter-
mine the energy levels of the DTQx-based conjugated
polymers (see Figure 3).21 CV curves were recorded in
referenced to an Ag/Agþ (0.01 M AgNO3 in acetonitrile)
electrode and calibrated by the ferrocene-ferrocenium
(Fc/Fcþ) redox couple (4.8 eV below the vacuum level).
ox
From the onset oxidation potential (E ) and onset reduc-
on
tion potential (Eroend) of the polymers, the HOMO and
LUMO energy levels as well as the electrochemical band
gaps (EEgC) were calculated (Table 1). The electrochemical
band gap EEgC coincides with the optical band gap estimated
from the UV-vis absorption onset for each of the copoly-
mers within the experimental error. All the DTQx-based
polymers had similar LUMO energy levels at -3.43 to
-3.48 eV. The HOMO energy level of PDTP-DTQx was
shifted upward by 0.45 eV compared with the HOMO
energy levels of the other three polymers, which reduced
the band gap of PDTP-DTQx.
Photovoltaic Properties. Bulk heterojunction type PSCs
were fabricated with a conventional sandwich structure,
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4894 Chem. Mater., Vol. 22, No. 17, 2010
Table 2. Device Characteristics of PSCs Based on the DTQx-Based Polymers in Combination with PCBM or PC70BM
Zhou et al.
polymer:acceptor (w/w)
solvent
VOC (V)
ISC (mA/cm2)
FF
PCE (%)
PF-DTQx (1:4)
PCBM
PCBM
PC70BM
PCBM
PC70BM
PCBM
PC70BM
PCBM
PC70BM
CB
CB:CF = 2:1
CB:CF = 2:1
CB
CB
CB
DCB
CB
DCB
0.86
0.86
0.86
0.76
0.76
0.84
0.80
0.46
0.46
4.77
5.75
6.75
4.49
7.26
3.86
7.38
5.25
7.78
0.43
0.56
0.55
0.42
0.40
0.48
0.43
0.48
0.49
1.75
2.78
3.23
1.43
2.20
1.56
2.54
1.17
1.77
PC-DTQx (1:3)
PIC-DTQx (1:4)
PDTP-DTQx (1:2)
DTBT-based polymers. When PCBM was used as the
electron acceptor, the PCEs of PSCs based on PF-DTBT,
PC-DTBT, PIC-DTBT, and PDTP-DTBT were 2.67,
3.05, 1.47, and 2.18%, respectively.12,20 The donor seg-
ment that gives the highest performance depends on the
acceptor segment (carbazole for DTBT and fluorene for
DTQx), revealing the complexity of choosing the proper
D-A combination for PSCs.
Figure 6 shows the external quantum efficiency (EQE)
plots of the optimized PSC devices with PF-DTQx:
PC70BM and PDTP-DTQx:PC70BM under the illumina-
tion of monochromatic light. In both cases, the shape of
the EQE plot is similar to the absorption spectrum of the
device, indicating that all the absorption wavelengths of
the polymers contributed to photocurrent generation.
Comparing the EQE plots and the absorption spectra of
the polymers in Figure 2, we can see that PC70BM
absorption contributes substantially to the photocurrent
by filling the valley of the polymer absorption. As a result,
the EQE of the device with PF-DTQx:PC70BM covers
most of the visible wavelength range from 300 to 700 nm,
and in the case of PDTP-DTQx:PC70BM, the EQE
response extends to 770 nm.
Figure 5. AFM height images of four DTQx-based polymers with
PCBM or PC70BM composite films, spin-coated from different solutions
(image size: 2 μm ꢀ 2 μm).
Conclusion
The combination of DTQx with four types of donor
segments in D-A type semiconducting polymers was
investigated for application to PSCs. The photovoltaic
properties of PSCs based on the four DTQx-based poly-
mers and PCBM or PC70BM were evaluated, and a
maximum PCE of 3.23% was achieved with PF-DTQx
by optimizing the conditions of device fabrication. The
results demonstrate that DTQx is a promising building
block that can be combined with many donor segments to
design efficient D-A type photovoltaic polymers.
Figure 6. EQE plots of PSCs based on PF-DTQx:PC70BM and PDTP-
DTQx:PC70BM.
Experimental Section
and PF-DTQx:PC70BM prepared from the mixture of CB
and CF was much more uniform, without extensive phase
separation.
Synthesis. All the chemicals were purchased from Alfa,
Aldrich or Wako and used without further purification. The
following compounds were synthesized according to procedures
in the literature:
For the other three polymers, uniform blend morpho-
logy was obtained merely by using suitable solvents. The
AFM images of PC-DTQx:PC70BM film spin-coated
from CB and PIC-DTQx:PC70BM and PDTP-DTQx:
PC70BM films spin-coated from DCB are also shown in
Figure 5. In the optimized conditions, the DTQx-based
polymers showed PCEs in the range of 1.17-3.23%; these
PCEs are comparable with those of the corresponding
5,8-di(2-bromothien-5-yl)-2,3-diphenylquinoxaline (monomer
3),19 2,7-bis-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-N-[1-
(20-ethylhexyl)-3-ethylheptanyl]carbazole (monomer 5),7 3,9-bis(4,
4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-5,11-di(1-decylundecyl)-
indolo[3,2-b]carbazole (monomer 6),13 and 2,6-di(trimethyl-
tin)-N-[1-(20-ethylhexyl)-3-ethylheptanyl]-dithieno[3,2-b:20,
30-d]pyrrole (monomer 7).12

Article
Synthesis of Poly{9,9-dioctylfluorene-2,7-diyl-alt-5,8-dithien-
Chem. Mater., Vol. 22, No. 17, 2010 4895
(CDCl3, 400 MHz): δ (ppm) 7.9-7.0 (m, 18H), 4.5 (br, 1H),
2.1-0.5 (m, 34H). Mn = 11.2 k; polydispersity = 1.4.
2-yl-2,3-diphenylquinoxaline-50,500-diyl} (PF-DTQx). Monomer
3 (230 mg, 0.38 mmol), monomer 4 (223 mg, 0.4 mmol), and
Aliquat 336 (∼50 mg) were dissolved in a mixture of toluene
(20 mL) and a 2 M aqueous solution of Na2CO3 (12 mL). The
reaction vessel was purged with N2 for 30 min to remove O2.
Pd(PPh3)4 (2%, 9 mg) was added, and the reaction mixture
was heated under reflux overnight (∼12 h). Phenylboronic acid
(100 mg in 1 mL THF) was added, and after 2 h, bromobenzene
(1 mL) was added. The mixture was allowed to reflux for 2 h and
cooled to room temperature. The polymer was precipitated by
slowly pouring the mixture into MeOH, filtered and Soxhlet
extracted with MeOH, hexane, and CHCl3. The CHCl3 solution
was passed through a column packed with alumina, Celite, and
silica gel. The column was eluted with CHCl3. The combined
polymer solution was concentrated and poured into MeOH.
The precipitate was then collected and dried under vacuum
overnight. Yield: 170 mg (51%). 1H NMR (CDCl3, 400 MHz): δ
(ppm) 8.2-7.4 (m, 22H), 2.12 (br, 4H), 1.2-0.7 (m, 30H). Mn =
8.1 k; polydispersity = 1.7.
Characterization. 1H NMR (400 MHz) spectra were mea-
sured on a JEOL Alpha FT-NMR spectrometer equipped with
an Oxford superconducting magnet system. Gel permeation
chromatography (GPC) was performed on a Shimadzu Promi-
nence system equipped with a UV detector(eluent: chloro-
form; 40 °C). The chloroform solution was filtered through a
PTFE filter (pore size: 1.0 μm) before sample injection.
UV-vis spectra were recorded on a JACSO V-650 spectro-
meter. Cyclic voltammograms (CVs) were recorded with an
HSV-100 (Hokuto Denkou) potentiostat. A Pt plate coated
with a thin polymer film was used as the working electrode. A
Pt wire and an Ag/Agþ (0.01 M of AgNO3 in acetonitrile)
electrode were used as the counter and reference electrodes
(calibrated vs Fc/Fcþ), respectively. AFM measurements
were carried out on a Digital Instrumental Nanoscope 31
operated in tapping mode.
Fabrication and Characterization of Polymer Solar Cell. PSCs
were constructed in the typical sandwich structure through
several steps. ITO-coated glass substrates were cleaned by
ultrasonication sequentially in detergent, water, acetone, and
2-propanol. After drying the substrate, PEDOT:PSS (Baytron
P) was spin-coated (4000 rpm for 30 s) onto ITO. The film was
dried at 150 °C under N2 atmosphere for 5 min. After cooling the
substrate, a solution of the DTQx-based polymer and PCBM (or
PC70BM) mixture was spin-coated onto the substrate inside a
nitrogen-filled glovebox. The substrate was annealed at 80 °C
for 30 min to remove the solvent. For the polymer/PCBM
system, an Al (30 nm) electrode was evaporated onto the
substrate under high vacuum (1 ꢀ 10-4 to 1 ꢀ 10-5 Pa) in an
evaporation chamber (ALS Technology H-2807 vacuum eva-
poration system with E-100 load lock). Postdeposition anneal-
ing was carried out at 110 °C for 5 min inside a nitrogen-filled
glovebox. For the polymer/PC70BM system, a Ca/Al (20 nm/60
nm) electrode was used and without postdeposition annealing.
The photovoltaic cells with no protective encapsulation were
subsequently tested in air under simulated air mass (AM) 1.5
solar irradiation (100 mW cm-2, Peccell Technologies PCE-
L11). Light intensity was adjusted by using a standard silicon
solar cell with an optical filter (Bunkou Keiki BS520). The
current-voltage characteristics of the photovoltaic cells were
measured on a Keithley 2400 I-V measurement system. The
effective areas of the PSCs were defined using a metal photo-
mask (2 mm ꢀ3 mm) during the irradiation of the simulated
solar light.22
Synthesis of Poly{N-[1-(20-ethylhexyl)-3-ethylheptanyl]carba-
zole-2,7-diyl-alt-5,8-dithien-2-yl-2,3-diphenylquinoxaline-50,500-diyl}
(PC-DTQx). PC-DTQx was prepared using the procedure for the
synthesis of PF-DTQx, but monomer 3 (172 mg, 0.285 mmol) and
monomer 5 (197 mg, 0.3 mmol) were used as starting materials.
1
Yield: 150 mg (62%). H NMR (CDCl3, 400 MHz): δ (ppm)
8.2-7.3 (m, 22H), 4.85 (br, 1H), 2.49 (br, 2H), 1.81 (br, 2H),
1.4-0.7 (m, 30H). Mn = 10.5 k; polydispersity = 1.9.
Synthesis of Poly{5,11-di(1-decylundecyl)indolo[3,2-b]carba-
zole-3,9-diyl-alt-5,8-dithien-2-yl-2,3-diphenylquinoxaline-50,500-diyl}
(PIC-DTQx). PIC-DTQx was prepared using the procedure for
the synthesis of PF-DTQx, but monomer 3 (157 mg, 0.26 mmol)
and monomer 6 (285 mg, 0.26 mmol) were used as starting
materials. Yield: 230 mg (90%). 1H NMR (CDCl3, 400 MHz): δ
(ppm) 8.4-7.3 (m, 24H), 4.75 (br, 2H), 2.50 (br, 4H), 2.05 (br, 4H),
1.4-0.9 (m, 76H). Mn = 21.1 k; polydispersity =1.6.
Synthesis of Poly{N-[1-(20-ethylhexyl)-3-ethylheptanyl]-dithieno-
[3,2-b:20,30-d]pyrrole-2,6-diyl-alt-5,8-dithien-2-yl-2,3-diphenylquino-
xaline-50,500-diyl} (PDTP-DTQx). Monomer 3 (249 mg, 0.412
mmol), monomer 7 (306 mg, 0.412 mmol), and dry toluene
(20 mL) were added to a 50 mL double-neck round-bottom flask.
The reaction vessel was purged with N2 for 30 min to remove O2.
Pd(PPh3)4 (3%, 14 mg) was added, and the mixture was heated to
110 °C. The solution was stirred at 110 °C for 48 h. The dark blue
sticky solution was cooled to room temperature and poured into
MeOH. The precipitates were collected by filtration and washed
with MeOH. The solid was dissolved in CHCl3 (150 mL) and
passed through a column packed with alumina, Celite, and silica
gel. The column was eluted with CHCl3. The combined polymer
solution was concentrated and poured into MeOH. The precipi-
(22) (a) Zhou, E. J.; Yamakawa, S.; Tajima, K.; Yang, C. H.; Hashi-
moto, K. Chem. Mater. 2009, 21, 4055. (b) Zhou, E. J.; Tajima, K.;
Yang, C. H.; Hashimoto, K. J. Mater. Chem. 2010, 20, 2362.
(c) Zhou, E. J.; Wei, Q. S.; Yamakawa, S.; Zhang, Y.; Tajima,
K.; Yang, C. H.; Hashimoto, K. Macromolecules 2010, 43, 821.
1
tates were collected and dried. Yield: 160 mg (45%). H NMR