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added dropwise. The mixture was stirred for 1 h at the same
temperature, and 1.0 M trimethyltin chloride in THF (15.7 mL,
15.74 mmol) was then added dropwise. The mixture was
slowly heated to room temperature and stirred overnight. The
mixture was quenched with water and then extracted with
dichloromethane. The organic layer was dried over Na2SO4 and
evaporated to produce the yellow viscous product with a yield
of 92.8% (5.48 g). 1H NMR(CDCl3, 400 MHz, d/ppm): 7.25–
7.24(d, 2H), 6.8(s, 2H), 2.9–2.81(m, 4H), 2.39–2.31(m, 4H),
1.81–1.73(m, 4H), 1.48–1.43 (br, 10H), 1.35–1.28 (br, 34H),
1.11–1.06 (m, 12H), 0.43–0.28 (t, 18H). Anal. calcd. for
Anal. calcd. for C76H100N2O2S4: C 75.95, H 8.39, N 2.33, O 2.66,
S 10.67; found: C 75.97, H 8.39, N 2.16, O 2.88, S 10.17.
RESULTS AND DISCUSSION
Polymer Synthesis
Scheme 1 shows the general synthetic routes for each poly-
mer. Three types of benzodithiophene derivatives and qui-
noxaline units were used for the synthesis. The polymers
were synthesized via a palladium-catalyzed Stille coupling
reaction at 100 ꢀC for 48 h, using toluene and Pd(0) as the
solvent and catalyst, respectively. At the end of the polymer-
ization, the mixture was end-capped by the sequential addi-
tion of 2-bromothiophene and 2-tributyl stannyl thiophene.
The mixture was then reprecipitated by adding methanol,
and a black powder was obtained. The obtained powders
were purified by sequential treatment with methanol, ace-
tone, hexane, and chloroform using a Soxhlet apparatus.
Finally, the chloroform-soluble portion was reprecipitated in
methanol. The obtained polymers dissolved readily in tetra-
hydrofuran (THF), chlorobenzene, and o-DCB. The structures
C56H90S4Sn2: C 59.58, H 8.03, S 11.36; found: C 58.95, H 7.93, S
10.34.
General Polymerization
Representative Procedure for Polymerization:
Polymerization of Poly[(4,8-di-(40-hexyl-20-decyl-thiophen-
50-yl)benzo[1,2-b:4,5-b0]dithiophene-2,6-diyl)-alt-5,8-bis(50-
thiophen-2-diyl)-2,3-diphenylquinoxaline)], PBDTDTQ-HDT
5,8-Bis(5-bromothiophen-2-yl)-2,3-diphenylquinoxaline (18
1.3 mg, 0.3 mmol) and tri(o-tolyl)phosphine (14.6 mg, 0.048
mmol) were dissolved in toluene (28 mL). The flask was
degassed and refilled with nitrogen gas twice, and then 2,6-
bis(trimethyltin)-4,8-di(2-decyl-4-hexyl-2-thienyl)-benzo [1,2-
b:4,5-b0]dithiophene (338.7 mg, 0.3 mmol) and tris(dibenzy-
lideneacetone)dipalladium(0) (10.98 mg, 0.012 mmol) were
added to the mixture. The flask was degassed and refilled
twice. The polymerization mixture was stirred at 110 ꢀC for
48 h, and a few drops of 2-bromothiophene were added.
After 3 min, a few drops of 2-tributylstannyl thiophene were
also added for the end-capping reaction. The reaction mix-
ture was cooled to room temperature and poured into meth-
anol. The precipitate was filtered and purified with methanol,
acetone, hexane, and chloroform in a Soxhlet apparatus. The
polymer was washed with ethylenediamine tetraacetic acid
(EDTA) and water, then extracted with solid phase extraction
(SPE) and precipitated in methanol. Finally, the polymer was
collected as a solid (60%, 229.9 mg) 1H NMR(CDCl3, 400
MHz, d/ppm): 8.2–7.9 (br, 2H), 7.9–7.5 (br, 8H), 7.5–7.2 (br,
6H), 7.2–7.1 (br, 2H), 7.1–6.8 (br, 2H), 3.2–2.8 (br, 4H), 2.6–
2.2 (br, 4H), 2.0–1.8 (br, 4H), 1.8–1.2 (br, 44H), 1.2–1.0 (br,
12H). Anal. calcd. for C78H90N2S6: C 75.07, H 7.27, N 2.24, S
15.42; found: C 73.36, H 7.16, N 2.20, S 14.0.
1
were analyzed using H NMR. Supporting Information Figure
S1 shows data confirming the successful synthesis of the pol-
y[benzodithiophene-alt-di-2-thienyl-quinoxaline]
series
(PBDTDPQ-EH, PBDTDPQ-OD, and PBDTDPQ-HDT). The
number-average molecular weights (Mn) of the synthesized
polymers were 9.8 kg mol21 for PBDTDPQ-EH, 24.3 kg
mol21 for PBDTDPQ-OD, and 20.0 kg mol21 for PBDTDPQ-
HDT. The polydispersity indexes (PDIs) were determined to
be 1.55, 2.86, and 1.88, respectively.
Optical and Electrochemical Properties
Figure 1 shows the UV–vis absorption spectra of the polymer
solutions in chloroform and of the films on a quartz plate.
For PBDTDPQ-EH and PBDTDPQ-OD, both of which have a
branched alkoxy chain in the DBT unit, two similar absorp-
tion peaks were observed in both the solution and film. In
the case of PBDTDPQ-EH, absorption peaks were detected at
406 and 555 nm for the solution and at 431 and 583 nm for
the film. In the case of PBDTDPQ-OD, absorption peaks were
found at 413 and 576 nm in solution and at 423 and 589
nm in the film state.
However, in the case of PBDTDPQ-HDT, which has a thio-
phene side chain in the BDT unit, three absorption peaks
were detected both in the solution (337, 404, and 544 nm)
and film (342, 418, and 568 nm) states. In particular, the
absorption peak around 340 nm was attributed to the thio-
phene side chain and was distinguishable from the other
two polymers. Similar results have been reported in other
studies of polymers with a 2D structure.9,11,23,24 The absorp-
tion peaks of the three polymers were red-shifted in solution
relative to the solid. Increasing the length of the alkoxy chain
from ethyl hexyl to octyl dodecyl also produced a slight red
shift in the absorption spectra. These shifts were attributed
to the improved solubility of the polymers with the extended
side chains and stable interaction among the polymers. In
contrast, the absorption spectra of the thiophene side-chain-
PBDTDPQ-EH and PBDTDPQ-OD were synthesized according to
the same procedure used for PBDTDTQ-HDT with the relevant
monomers. 1H NMR, gel permeation chromatography (GPC)
data, and elemental analysis for the polymers are presented,
except for elemental analysis of PBDTDPQ-EH due to low yield.
PBDTDPQ-EH.
19%, 50 mg, 1H NMR(CDCl3, 400 MHz, d/ppm): 7.9–7.5 (br,
8H), 7.5–7.2 (br, 6H), 7.2–7.1 (br, 2H), 7.1–6.8 (br, 2H), 4.3–3.9
(br, 4H), 2.0–1.8 (br, 2H), 1.8–1.2 (br, 12H), 1.2–1.0 (br, 12H).
PBDTDPQ-OD.
1
83%, 302 mg, H NMR(CDCl3, 400 MHz, d/ppm): 7.9–7.5 (br,
8H), 7.5–7.2 (br, 6H), 7.2–7.1 (br, 2H), 7.1–6.8 (br, 2H), 4.3–3.9
(br, 4H), 2.0–1.8 (br, 2H), 1.8–1.2 (br, 64H), 1.2–1.0 (br, 12H).
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JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 1028–1036