Synthesis and characterization of new selenophene-based donor-acceptor low-bandgap polymers for organic photovoltaic cells

Article abstract of DOI:10.1021/ma2020112

A series of novel thiophene- and selenophene-based low-bandgap polymers were synthesized using a Stille cross-coupling reaction; these polymers contained quinoxaline and diketopyrrolopyrrole as acceptors. Various acceptors were introduced into the selenophene backbones, and the solubility, absorption spectra, energy levels, charge transport, blend film morphology, and photovoltaic properties of the resulting polymers were investigated. The weight-averaged molecular weights (M_w) of P3TDTQ, P3SDTQ, P3TDTDPP, and P3SDTDPP were found to be 12 300, 15 500, 13 300, and 17 200, with polydispersity indices of 1.46, 1.85, 1.58, and 1.63, respectively. Photophysical studies revealed low bandgaps of 1.70 eV for P3TDTQ, 1.63 eV for P3SDTQ, 1.27 eV for P3TDTDPP, and 1.25 eV for P3SDTDPP; the films could harvest a broad solar spectrum, covering the range from 300 to 800 nm (P3TDTQ and P3SDTQ) and from 350 to 950 nm (P3TDTDPP and P3SDTDPP). Solution-processed field-effect transistors fabricated from these polymers had p-type organic thin film transistor characteristics. The field-effect mobilities of P3TDTQ, P3SDTQ, P3TDTDPP, and P3SDTDPP were measured to be 2.8 × 10^-5, 5.0 × 10^-5, 1.0 × 10^-3, and 2.1 × 10 ^-3 cm² V^-1 s^-1, respectively. The novel polymers were combined with a PCBM ([6,6]-phenyl C₇₁-butyric acid methyl ester) acceptor to fabricate bulk heterojunction solar cells, which produced power conversion efficiencies of 0.64-3.18% under AM 1.5 G (100 mW/cm²) conditions.

Full text of DOI:10.1021/ma2020112

Article
pubs.acs.org/Macromolecules
Synthesis and Characterization of New Selenophene-Based Donor−
Acceptor Low-Bandgap Polymers for Organic Photovoltaic Cells
Woo-Hyung Lee,† Seon Kyoung Son,‡ Kyoungkon Kim,‡ Sang Kyu Lee,§ Won Suk Shin,§
Sang-Jin Moon,§ and In-Nam Kang*,†
†Department of Chemistry, The Catholic University of Korea, Bucheon, Korea
‡Solar Cell Research Center, Korea Institute of Science and Technology, Seoul, Korea
§Energy Materials Research Division, Korea Research Institute of Chemical Technology, Daejeon, Korea
S
* Supporting Information
ABSTRACT: A series of novel thiophene- and selenophene-
based low-bandgap polymers were synthesized using a Stille cross-
coupling reaction; these polymers contained quinoxaline and
diketopyrrolopyrrole as acceptors. Various acceptors were
introduced into the selenophene backbones, and the solubility,
absorption spectra, energy levels, charge transport, blend film
morphology, and photovoltaic properties of the resulting polymers
were investigated. The weight-averaged molecular weights (Mw) of
P3TDTQ, P3SDTQ, P3TDTDPP, and P3SDTDPP were found
to be 12 300, 15 500, 13 300, and 17 200, with polydispersity
indices of 1.46, 1.85, 1.58, and 1.63, respectively. Photophysical
studies revealed low bandgaps of 1.70 eV for P3TDTQ, 1.63 eV
for P3SDTQ, 1.27 eV for P3TDTDPP, and 1.25 eV for
P3SDTDPP; the films could harvest a broad solar spectrum, covering the range from 300 to 800 nm (P3TDTQ and
P3SDTQ) and from 350 to 950 nm (P3TDTDPP and P3SDTDPP). Solution-processed field-effect transistors fabricated from
these polymers had p-type organic thin film transistor characteristics. The field-effect mobilities of P3TDTQ, P3SDTQ,
P3TDTDPP, and P3SDTDPP were measured to be 2.8 × 10−5, 5.0 × 10−5, 1.0 × 10−3, and 2.1 × 10−3 cm2 V−1 s−1, respectively.
The novel polymers were combined with a PCBM ([6,6]-phenyl C71-butyric acid methyl ester) acceptor to fabricate bulk
heterojunction solar cells, which produced power conversion efficiencies of 0.64−3.18% under AM 1.5 G (100 mW/cm2)
conditions.
of thiophene as a donating moiety and quinoxaline (Qx) and
diketopyrrolopyrrole (DPP) as accepting moieties has been
closely investigated and provides a successful strategy to achieve
low-bandgap materials.11,12 Compared with their thiophene
analogues, selenophene-containing polymers have been studied
to a lesser extent, possibly due to the difficulties associated with
their synthesis. As a class, polyselenophenes are expected to
have advantages over polythiophenes. For example, interchain
charge transfer should be facilitated by the intermolecular Se−
Se contact, which means that polyselenophenes should have
higher bulk conductivities and mobilities than polythio-
phenes.13 Furthermore, selenophene substitution in conjugated
polymers reduces the bandgap energy, mainly by stabilizing the
lowest unoccupied molecular orbital (LUMO) level more
effectively than the corresponding polythiophenes.14−16 Poly(3-
hexylselenophene) (P3HS) displays a bandgap energy (1.6 eV)
lower than that of P3HT (1.9 eV).15 The photovoltaic
INTRODUCTION
■
Organic solar cells based on conjugated polymers have the
potential to be applied as a clean energy source. In addition,
such cells have the advantages that they can be fabricated at low
cost via solution-based processing and that they have
mechanical flexibility appropriate for foldable or rollable
substrates.1−4 Bulk-heterojunction (BHJ) devicesin which a
donor polymer (p-type) is blended with a fullerene derivative
or other acceptor (n-type) materialhave emerged as the most
efficient polymer solar cells (PSCs) developed to date.5−7 One
of the main factors limiting the performance of PSCs is the
mismatch between their absorption and the terrestrial solar
spectra. Polymer materials with low bandgaps are therefore
needed to harvest solar photons at longer wavelengths,
particularly in the near-IR region, and with a broader spectrum.
Conjugated polymers that incorporate alternating donor and
acceptor units produce significant decreases in the bandgap,
due to the introduction of intramolecular charge transfer (ICT)
structures.8−10 Several types of donor−acceptor (D−A)
conjugated copolymers have been synthesized for use in high-
performance organic photovoltaic (OPV) applications. The use
Received: September 2, 2011
Revised: December 12, 2011
Published: January 31, 2012
© 2012 American Chemical Society
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Scheme 1. Synthetic Routes for the Monomers
Scheme 2. Synthesis of the Low-Bandgap Polymers P3TDTQ, P3SDTQ, P3TDTDPP, and P3SDTDPP
properties of P3HS:PCBM devices result in a high power
conversion efficiency (2.7%) because P3HS provides a more
extensive photon absorption cross section than P3HT.14
Poly(3,3-dialkylterselenophene) (PSSS) also exhibits high
charge-carrier mobilities and ambipolar behaviors in organic
field effect transistor devices; the low LUMO energy levels are
thought to facilitate both electron injection and transport.16
Recently, several groups have reported the use of selenophene-
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based D−A copolymers (with a selenophene donor and various
acceptors) for organic transistors, but the solar cell perform-
ances of these polymers have not yet been reported.17,18 Here,
we report the synthesis, optical and physical properties, and
OPV performances of novel selenophene-based D−A low-
bandgap polymers. These polymers were synthesized using a
Stille cross-coupling reaction, with terselenophene as a donor
and quinoxaline (Qx) and diketopyrrolopyrrole (DPP) as
acceptors. The Qx-containing polymers are denoted as
P3SDTQ, and those containing DPP are denoted as
P3SDTDPP. These polymers have lower bandgaps in π-
conjugated polymers, thereby increasing the overall photon
absorption by extending the spectral sensitivity. We examined
the effects of the incorporation of different acceptors in the
selenophene backbones on the absorption, energy levels, charge
transport properties, morphologies, and photovoltaic properties
of the donor/acceptor blends. In addition, terthiophene-based
D−A polymers (with terthiophene as a donor and quinoxaline
(Qx) (P3TDTQ) and diketopyrrolopyrrole (DPP)
(P3TDTDPP) as acceptors) were also synthesized using the
same polymerization method, to allow a comparison between
the optoelectronic and photovoltaic properties of the
terthiophene-based D−A polymers and those of the
selenophene-based polymers.
RESULTS AND DISCUSSION
■
Synthesis and Characterization. The synthetic routes to
the monomers and polymers are shown in Schemes 1 and 2,
respectively. As shown in Scheme 1, a branched alkyl chain was
introduced at the 3-position of the thiophene and selenophene
rings to increase the solubility of the D−A copolymers.
Compounds 1 and 4 were converted into the dibromo
compounds 5 and 6 with N-bromosuccinimide (NBS) in the
presence of a polar protic solvent, with good yields.
Compounds 7 and 8 were synthesized according to methods
described in the literature.19,20 Compounds 9 and 10 were
synthesized using the Stille coupling reaction, via the
condensation of the distannyl compounds 7 and 8 and the
corresponding brominated compounds 5 and 6. Compounds
11 and 12 were synthesized from compounds 9 and 10 by
distannylation, with good yields (68−91%). The P3TDTQ,
P3SDTQ, P3TDTDPP, and P3SDTDPP polymers were
obtained via the combinatorial Stille coupling reaction of
compounds 11 and 12 with compounds 13 and 14. The
synthetic routes used to synthesize the P3TDTQ, P3SDTQ,
P3TDTDPP, and P3SDTDPP polymers are also described in
Scheme 2. The weight-average molecular weights (Mw) of
P3TDTQ, P3SDTQ, P3TDTDPP, and P3SDTDPP were
determined using gel permeation chromatography (GPC),
using a polystyrene standard in a chloroform eluent; they were
found to be 12 300 (PDI = 1.46), 15 500 (PDI = 1.85), 13 300
(PDI = 1.58), and 17 200 (PDI = 1.63), respectively. The
polymer readily dissolved in common organic solvents such as
toluene, chloroform, and THF and formed good films. Thermal
analysis of the polymers was conducted using differential
scanning calorimetry (DSC), and thermogravimetric analysis
(TGA), as shown in Figure 1. The results showed that both
polymers had good thermal stability over 300 °C, and no
obvious thermal transitions were observed between 50 and 200
°C. The polymerization results for the synthesized copolymers
are summarized in Table 1.
Figure 1. (a) TGA and (b) DSC of P3TDTQ, P3SDTQ, P3TDTDPP,
and P3SDTDPP, performed at a heating rate of 10 °C min−1 under an
inert atmosphere.
Table 1. Physical Properties of the Synthesized Polymers
a
polymer
Mn (g/mol)
Mw (g/mol)
PDI
Td (°C)
P3TDTQ
8.39K
9.31K
8.43K
10.5K
12.3K
15.5K
13.3K
17.2K
1.46
1.85
1.58
1.63
384
336
395
394
P3SDTQ
P3TDTDPP
P3SDTDPP
a
Decomposition temperature at 5% weight loss.
copolymers in a dilute chlorobenzene solution and in thin films;
the absorption data for the polymers are summarized in Table
2. The λmax of P3TDTQ, P3SDTQ, P3TDTDPP, and
P3SDTDPP in solution occurred at 549, 599, 679, and 702
nm, respectively, whereas those in the thin films occurred at
587, 619, 716, and 753 nm, respectively; these values were
significantly red-shifted compared with those of poly(3,3-
dialkylterthiophene) (PTT, λmax,film = 510 nm) and poly(3,3-
dialkylterselenophene) (PSSS, λmax,film = 614 nm).16,21 The
UV−vis absorption spectra of the P3S-based polymers
(P3SDTQ and P3SDTDPP) were red-shifted by about 20−
50 nm with respect to those of the P3T-based polymers
(P3TDTQ and P3TDTDPP), both in solution and in thin
films; this resulted from the presence of selenium atoms in the
polymer repeat units. Selenium atoms are more electron-rich
than sulfur atoms; hence, aromatic rings containing selenium
Optical and Electrochemical Properties. The UV−vis
absorption spectra of the copolymers are shown in Figure 2 for
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lower than those found for poly(3,3-dialkylterthioophene)
(PTT, 2.1 eV) and poly(3,3-dialkylterselenophene) (PSSS, 1.8
eV). This successful reduction in the bandgap was mainly due
to intramolecular charge transfer (ICT) effects between the
terthiophene donor or terselenophene donors and the Qx or
DPP acceptor groups. The DPP moiety was a stronger acceptor
than Qx, which led to a smaller Eg for P3TDTDPP and
P3SDTDPP than for P3TDTQ and P3SDTQ. The low
bandgaps of P3TDTDPP (1.27 eV) and P3SDTDPP (1.25
eV) may have resulted from the planarity and high degree of
conjugation in the DPP acceptor, which would enhance the
π−π interactions and ICT among the polymer main
chains.24−26 Moreover, the optical bandgaps of the P3S-based
polymer thin films were smaller than those of the P3T-based
polymers because of the electron-rich selenium atoms in the
core repeat units. The significant broadening in the absorption
spectra of P3TDTDPP and P3SDTDPP (relative to P3TDTQ
and P3SDTQ) may have indicated better ordering of the
molecules in the bulk phase, which was manifested in the
behavior of the external quantum efficiency (EQE).
Cyclic voltammograms (CV) are shown in Figure 3 for the
polymers. These measurements were performed in an electro-
Figure 2. UV−vis spectra of P3TDTQ, P3SDTQ, P3TDTDPP, and
P3SDTDPP (a) in chlorobenzene solution and (b) in thin films.
Table 2. UV−vis Maximum Absorption Wavelength (λmax),
Bandgap Energy (Eg), and Ionization Potential (EHOMO) of
a
P3TDTQ, P3SDTQ, P3TDTDPP and P3SDTDPP
solution
film
(λmax, nm) (eV)
Egopt
E
HOMcO
ELUMO
Figure 3. Cyclic voltammograms for the polymer films on ITO glass,
performed at a scanning rate of 50 mV s−1, in acetonitrile containing
0.1 M n-Bu4NBF4.
a
b
polymer
(λmax, nm)
(eV)
(eV)
P3TDTQ
431, 549
428, 599
679
436, 587
427, 619
716
1.70
−5.37
−5.35
−5.21
−5.16
−3.67
−3.72
−3.94
−3.91
P3SDTQ
1.63
1.27
1.25
P3TDTDPP
P3SDTDPP
lyte solution of 0.1 M tetrabutylammonium tetrafluoroborate
(TBABF4) in anhydrous acetonitrile, at room temperature and
under nitrogen, with a scan rate of 50 mV/s. The HOMO levels
of the polymer films were estimated from the cyclic
voltammograms, using the equation EHOMO = −(Eox + 4.8)
eV, where Eox is the onset oxidation potential relative to the
ferrocene standard material.27 The highest occupied molecular
orbital (HOMO) energy levels of P3TDTQ, P3SDTQ,
P3TDTDPP, and P3SDTDPP were calculated to be −5.37,
−5.35, −5.21, and −5.16 eV, respectively, using the ferrocene
reference value of −4.8 eV below the vacuum level. The LUMO
levels of P3TDTQ, P3SDTQ, P3TDTDPP, and P3SDTDPP
were calculated to be −3.67, −3.72, −3.94, and −3.91 eV,
respectively, as estimated from the optical bandgaps and
HOMO energy levels. The deep HOMO levels may have
contributed to the improved oxidative stability and higher
open-circuit voltage (Voc) compared with those of PTT (−5.2
eV) and PSSS (−4.9 eV).16 The above results indicated that the
bandgap and molecular energy levels of P3T- or P3S-based
702
753
a
b
Measurements performed in chlorobenzene. Estimated from the
onset of the absorption in thin films (Eg = 1240/λonset eV). Calculated
using the optical bandgap energy.
c
are more easily delocalized than those containing sulfur
atoms.15,22,23 Moreover, the absorption spectra of the DPP-
containing polymers (P3TDTDPP and P3SDTDPP) were red-
shifted by over 130 nm compared with the spectra of the Qx-
containing polymers (P3TDTQ and P3SDTQ), suggesting the
presence of stronger π−π interchain associations and
aggregation in the solid state. Such aggregation is beneficial
for improving charge mobility in thin films. The optical
bandgaps of the polymer thin films were determined from the
UV−vis absorption onsets in the solid state (Eg = 1240/λonset
eV). The optical bandgaps (Eg) in the thin films were 1.70,
1.63, 1.27, and 1.25 eV for P3TDTQ, P3SDTQ, P3TDTDPP,
and P3SDTDPP, respectively; these values were significantly
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polymers could be efficiently tuned by incorporating
appropriate electron-withdrawing Qx and DPP groups. The
electrochemical potentials are summarized in Table 2.
Field-Effect Transistor Characteristics. The effects of the
shape and position of the side chains on the electrical transport
properties of the resulting polymers were examined by
measuring the field-effect transistor (FET) mobility. The
field-effect carrier mobilities of the polymers were investigated
by fabricating thin-film transistors with a bottom-contact
geometry, using Au electrodes. The FET characteristics were
determined under ambient conditions, and no precautions were
taken to insulate the materials and devices from exposure to air,
moisture, or light. The field-effect mobility was calculated
according to the equation28
saturated regime (V > V ):
D
G
2
I = (W/2L)μC (V − V )
D
i
G
T
Figure 4. J−V characteristics of a photovoltaic device using polymer/
PC61BM blend films as active layers.
where ID is the drain current in the saturated regime, W and L
are the channel width and length, respectively, μ is the field-
effect mobility, Ci is the capacitance per unit area of the gate
dielectric layer, and VG and VT are the gate and threshold
voltages, respectively. The P3TDTQ, P3SDTQ, P3TDTDPP,
and P3SDTDPP samples exhibited typical p-type organic
semiconductor characteristics, with hole mobilities of 2.8 ×
10−5, 5.0 × 10−5, 1.0 × 10−3, and 2.1 × 10−3 cm2 V−1 s−1,
respectively. The results are plotted in Figure S1 (Supporting
Information). The hole mobility values for the P3S-based
polymers were ∼1.5 times higher than those for the P3T-based
polymers. The hole mobilities of the DPP-containing polymers
(P3TDTDPP and P3SDTDPP) were 2 orders of magnitude
higher than those of the Qx-containing polymers (P3TDTQ
and P3SDTQ). The higher mobilities measured for
P3TDTDPP and P3SDTDPP can be understood in terms of
an improved intermolecular π−π stacking, which corresponds
well with the UV−vis results. In addition, P3TDTDPP and
P3SDTDPP yielded higher hole mobilities than P3TDTQ and
P3SDTQ; this was attributed to the more efficient charge
extraction in the P3TDTDPP and P3SDTDPP solar cell
devices (Table 3).
of the Qx-containing polymer devices was higher for a blend
ratio of 1:3 than 1:1, while for DPP-containing polymer devices,
the PCE was better with a 1:1 blend ratio than with a ratio of
1:3. The PCEs of the P3TDTQ, P3SDTQ, P3TDTDPP, and
P3SDTDPP devices were found to be 0.30%, 0.52%, 1.88%,
and 1.85%, respectively. The open-circuit voltages (VOC, which
is related to the difference between the HOMO level of the
donor polymer and the LUMO level of the acceptor
(PC61BM)) of the P3TDTQ, P3SDTQ, P3TDTDPP, and
P3SDTDPP devices were found to be 0.68, 0.67, 0.56, and 0.50
V, respectively, for a blend ratio of 1:1. The high VOC values for
the P3TDTQ and P3SDTQ devices could be explained by the
low HOMO energy levels of P3TDTQ (−5.37 eV) and
P3SDTQ (−5.35 eV) compared with those of P3TDTDPP
(−5.21 eV) and P3SDTDPP (−5.16 eV). Among the devices
using the P3T- and P3S-based polymers, the P3TDTDPP and
P3SDTDPP devices demonstrated better photovoltaic perform-
ances than did those using P3TDTQ and P3SDTQ because the
photon absorption fraction and the FET mobility were higher
in the DPP-containing polymer films than in those containing
Qx. The DPP-containing polymer devices therefore exhibited a
high short circuit current density (JSC). In the case of the Qx-
containing polymer devices, the P3S-Qx devices showed higher
PCE values than their thiophene analogues; however, the PCEs
of the P3S-DPP devices were slightly lower than those of the
P3T-DPP devices. The PCEs of the P3T-and P3S-based
devices were heavily dependent on the electron-withdrawing
accepting units. Interestingly, regardless of the PCE values of
the devices, the P3S-based devices (Qx and DPP) always
showed higher JSC values than the corresponding thiophene
analogues (for the same PCBM blend ratio). The increased
short circuit currents of the P3S-based devices could be
attributed to the increased spectral breadth of the absorbed
photons and hole mobilities. To better understand the origin of
the differences in the photovoltaic performances of the polymer
solar cells, AFM images of the surface morphologies of each
solar cell device were collected (Figure S2, Supporting
Information). Generally, nanoscale phase separation should
be established to allow efficient charge separation; this is true
due to the short exciton diffusion length (∼10 μm) of the
donor polymers.29 As can be seen in Figure S2, the
P3TDTDPP:PCBM (1:1) and P3SDTDPP:PCBM (1:1)
films showed a smoother and more interconnected network
Table 3. PSC Performances of the Polymer/PC61BM Device
polymer
ratio JSC (mA/cm2) VOC (V) FF (%) PCE (%)
P3TDTQ
1:1
1:3
1:1
1:3
1:1
1:3
1:1
1:3
1.29
1.82
2.12
2.48
6.50
5.25
9.18
6.45
0.68
0.67
0.67
0.63
0.56
0.56
0.50
0.51
34
46
35
45
51
51
40
41
0.30
0.56
0.52
0.72
1.88
1.49
1.85
1.36
P3SDTQ
P3TDTDPP
P3SDTDPP
Organic Photovoltaic Characteristics. Polymer solar cell
devices were fabricated using the P3T- and P3S-based polymers
as electron donors and [6,6]-phenyl C61-butyric acid methyl
ester (PC61BM) as an electron acceptor. The device structure
was ITO/PEDOT:PSS(50 nm)/polymer:PC61BM/LiF(0.6
nm)/Al(130 nm). The photovoltaic performances of the
polymer:PC61BM devices are summarized in Table 3 and
Figure 4. The PCEs varied considerably with the poly-
mer:PCBM blend ratio used in the devices; the details of the
variation depended on the polymer backbone. Thus, the PCE
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of polymer−PCBM domains, which accounted for the high
photocurrent density in these films. In contrast, relatively high
levels of aggregation were observed in the P3TDTQ:PCBM
(1:1) and P3SDTQ:PCBM (1:1) films, which reduced the area
for charge separation, leading to a low photocurrent. There
were no significant differences between the morphologies of the
P3T-based films and those of the P3S-based films.
The performances of the solar cells based on
P3TDTDPP:PCBM (1:1) and P3SDTDPP:PCBM (1:1)
films were further enhanced via the use of [6,6]-phenyl C71-
butyric acid methyl ester (PC71BM) as an electron acceptor and
the use of a mixed chlorobenzene (CB)/1,8-diiodoctane (DIO)
(97%:3% by volume) solvent. Figure 5 shows the current−
Table 4. PSC Performances of the Polymer/PC71BM Device
polymer
ratio
1:1
JSC (mA/cm2) VOC (V) FF (%) PCE (%)
P3TDTDPP
5.21
10.65
7.86
0.55
0.54
0.50
0.51
58
56
45
45
1.65
3.18
1.77
2.81
a
1:1
P3SDTDPP
1:1
a
1:1
12.33
a
3% DIO additive (v/v).
P3SDTDPP:PC71BM (1:1) device. In this case, the PCE of
the P3SDTDPP device was slightly lower than that of the
P3TDTDPP device, due to the low VOC and FF; however, the
JSC of the P3SDTDPP device was higher than that of the
P3TDTDPP device, which was attributed to the lower bandgap
and higher mobility of the P3SDTDPP film (compared with
the P3TDTDPP film). The improvement in the OPV
performances was caused by the changes in the morphology
of the blend film. AFM images (Figure. 6) clearly showed that
there were large domains in the blend film prepared using only
chlorobenzene; these large domains would diminish exciton
migration to the donor/acceptor interface and are not favorable
for charge separation. The morphology of the blend film
prepared using the chlorobenzene/DIO mixed solvent was
much more uniform, with no significant phase separation.
Good miscibility between the donor polymer and the PC71BM
was shown, and interpenetrating networks were formed; these
factors may have led to increases in the JSC value.
EQE values (which were measured to evaluate the
photoresponses of the fabricated solar cells as a function of
wavelength) are shown in Figure 5b for the
P3TDTDPP:PC71BM (1:1) and P3SDTDPP:PC71BM (1:1)
devices prepared with 3% DIO. The P3TDTDPP and
P3SDTDPP devices yielded an EQE plot that was similar to
the absorption spectra of P3TDTDPP and P3SDTDPP in the
long wavelength region, indicating that excitons were mainly
generated in the polymer phase. The spectral responses of the
P3TDTDPP device showed that in the region from 350 to 950
nm photons contributed significantly to the EQE, with a
maximum EQE of 35% at 550 nm. The P3SDTDPP device,
however, exhibited an even better spectral response in the range
350−1000 nm, with a maximum EQE of 38% at 550 nm. The
P3SDTDPP:PC71BM blend film exhibited a wide absorption
spectrum (650−1000 nm), which resulted in a much higher JSC
of 12.33 mA/cm2.
CONCLUSIONS
■
In summary, we successfully synthesized novel thiophene- and
selenophene-based low-bandgap polymers, using the Stille
coupling reaction. The P3TDTQ P3SDTQ, P3TDTDPP, and
P3SDTDPP polymers showed good solubility in common
organic solvents because of the presence of alkyl side chains.
P3TDTQ, P3SDTQ, P3TDTDPP, and P3SDTDPP exhibited
long-wavelength UV−vis absorption peaks at 587, 619, 716,
and 753 nm, respectively. The P3SDTDPP:PC71BM blend film
showed a wide absorption spectrum (650−1000 nm), which
resulted in a much higher JSC of 12.33 mA/cm2. A photovoltaic
device using the P3TDTDPP:PC71BM (1:1) and
P3SDTDPP:PC71BM (1:1) films with added DIO as the active
layer exhibited open-circuit voltages of 0.54 and 0.51 V, short-
circuit current densities of 10.65 and 12.33 mA/cm2, fill factors
of 0.56 and 0.45, and power conversion efficiencies of 3.18 and
2.81% for the two films, respectively, under AM 1.5G (100
mW/cm2) illumination. We believe that the VOC and FF values
Figure 5. (a) J−V characteristics of a photovoltaic device using
P3TDTDPP/PC71BM (1:1) and P3SDTDPP/PC71BM (1:1) and (b)
external quantum efficiency of the P3TDTDPP/PC71BM (1:1) and
P3SDTDPP/PC71BM (1:1) blend films prepared from mixed CB/
DIO (97/3, v/v) solvents.
voltage characteristics resulting from the use of the PC71BM
and the mixed solvent in the polymer solar cell devices; the data
are summarized in Table 4. The P3TDTDPP:PC71BM (1:1)
and P3SDTDPP:PC71BM (1:1) devices showed PCE values
similar to those shown by the corresponding PC61BM devices.
In contrast, dramatic improvements were observed in the JSC
and PCE values for the 3% DIO-containing devices. The PCE
increased from 1.88% to 3.18% for the P3TDTDPP:PC71BM
(1:1) device and from 1.85% to 2.81% for the
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Figure 6. AFM tapping-mode height images of (a) P3TDTDPP/PC71BM (1:1), (b) P3SDTDPP/PC71BM (1:1), (c) P3TDTDPP/PC71BM (1:1) +
3% DIO, and (d) P3SDTDPP/PC71BM (1:1) + 3% DIO. The scanned area is 2 μm × 2 μm.
3-(3′,7′-Dimethyoctyl)thiophene (1). A 1.0 M solution 3,7-
dimethyloctylmagnesium bromide (50 mL, 0.05 mol) was added
dropwise to a solution of 3-bromothiophene (6.24 g, 0.04 mol) and
Ni(dppp)Cl2 (0.67 g, 1.2 mmol) in THF (60 mL) at −20 °C with
stirring. The mixture was stirred at RT for 4 h and then poured into
water (100 mL) and extracted with ethyl acetate. After drying over
anhydrous MgSO4, the solvent was evaporated and the residue was
purified by column chromatography on silica gel with hexane as eluent.
After drying, the product was obtained as colorless oil. Yield: 6.3 g
(70%). Fab-MS: m/z = 225. 1H NMR (300 MHz, CDCl3, δ): 7.22 (d,
1H), 6.92 (s, 1H), 6.90 (d, 1H), 2.61 (m. 2H), 1.1−1.50 (m. 10H),
0.91 (d, 3H), 0.87 (d, 6H). 13C NMR (80 MHz, CDCl3, δ): 143.64,
128.48, 125.25, 119.83, 39.54, 38.05, 37.36, 32.69, 28.19, 28.19, 24.93,
22.93, 22.84, 19.79. Anal. Calcd for C14H24Se: C 74.93, H 10.78, S
41.29. Found: C 74.70, H 10.41, S 14.47.
1-Chloro-5,9-dimethyldecan-2-one (2). A 1.0 M solution 3,7-
dimethyloctylmagnesium bromide (100 mL, 0.1 mol) was added
dropwise to a solution of chloroacetyl chloride (16 mL, 0.2 mol) in
THF (30 mL) at −78 °C with stirring. The mixture was stirred at −78
°C for 6 h and then poured into water (100 mL) and extracted with
ethyl acetate. After drying over anhydrous MgSO4, the solvent was
evaporated. The product was used without further purification. Yield:
7.5 g (34%).
could be improved by the use of different solvents and/or a
buffer layer. With enhanced VOC and FF values, the
performance of the P3S-based polymer solar cells could be
improved.
EXPERIMENTAL SECTION
■
Instrumentation. 1H and 13C NMR spectra were recorded on
Bruker AVANCE 400 spectrometer, with tetramethylsilane as an
internal reference. The optical absorption spectra were measured by a
Shimadzu UV-3100 UV−vis−NIR spectrometer. The number- and
weight-average molecular weights of polymers were determined by gel
permeation chromatography (GPC) on Viscotek T60A instrument,
using chloroform as eluent and polystyrene as standard. The
differential scanning calorimetry (DSC) and thermal gravimetric
analysis were made using TA Q100 instrument and operated under a
nitrogen atmosphere. Cyclic voltammetry was performed on an
AUTOLAB/PG-STAT12 model system with a three-electrode cell in a
solution of Bu4NBF4 (0.10 M) in acetonitrile at a scan rate of 50 mV/
s. Polymer film coatings on ITO anode electrode were formed by the
spin-coating method. Atomic force microscopy (AFM) was measured
by tapping-mode using Multimode IIIa, Digital Instruments. Electrical
characteristics of the TFTs were measured in ambient conditions using
both Keithley 2400 and 236 source/measure units. For all measure-
ments, we used channel lengths (L) of 12 μm and channel widths (W)
of 120 μm. Field effect mobility was extracted in the saturation regime
from the slope of the source-drain current.
3-(Chloromethyl)-6,10-dimethylundec-1-yn-3-ol (3). A 0.5 M
solution of ethynylmagnesium bromide (100 mL, 0.05 mol) was added
dropwise to a solution of compound 2 (7.5 g, 0.035 mol) in THF (150
mL) at −60 °C with stirring. The mixture was stirred at −60 °C for 4
h and then poured into water (150 mL) and extracted with ethyl
acetate. After drying over anhydrous MgSO4, the solvent was
evaporated and the residue was purified by column chromatography
on silica gel with hexane as eluent. After drying, the product was
Materials. 2,5-Bis(trimethylstannyl)thiophene (7),19 2,5-bis-
(trimethylstannyl)selenophene (8),20 2,3-bis(4-(3,7-dimetyloctyloxy)-
phenyl)-5,8-bis(5′-bromodithien-2-ly)quinoxaline (13),30 and 3,6-bis-
(5-bromothiophene-2-yl)-2,5-bis(2-ethylhexyl)pyrrolo[3,4-c]pyrrole-
1,4(2H,5H)-dione (14)31 were synthesized according to previously
published procedures.
1
obtained as colorless oil. Yield: 4.0 g (48%). Fab-MS: m/z = 243. H
NMR (300 MHz, CDCl3, δ): 3.67 (d, 1H), 3.61 (d, 1H), 2.57 (s, 1H),
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1
2.51 (s. 1H), 1.2−1.7 (m. 9H), 1.1 (m, 3H), 0.87 (m, 9H). 13C NMR
(80 MHz, CDCl3, δ): 83.89, 73.88, 70.92, 53.18, 39.48, 37.28, 37.13,
36.88, 33.01, 31.23, 28.17, 24.91, 22.91, 19.83. Anal. Calcd for
C14H25ClO: C 68.69, H 10.29, O 6.54. Found: C 67.76, H 10.14, O
6.9.
solid. Yield: 1.0 g (78%). Fab-MS: m/z = 528. H NMR (300 MHz,
CDCl3, δ): 7.17 (d, 2H), 7.05 (d, 2H), 6.92 (s, 2H), 2.80 (m. 4H),
1.13−1.70 (m. 20H), 0.91 (d, 6H), 0.87 (d, 12H). 13C NMR (80
MHz, CDCl3, δ): 140.08, 136.27, 130.54, 130.23, 126.25, 124.01,
39.53, 38.21, 37.35, 33.07, 28.20, 27.18, 24.96, 22.92, 22.83, 19.84.
Anal. Calcd for C32H48S3: C 72.67, H 9.15, S 18.19. Found: C 72.70, H
9.02, S 18.14.
3-(3′,7′-Dimethyoctyl)selenophene (4). A solution selenium (2
g, 0.025 mol) and sodium borohydride (1.84 g, 0.048 mol) was
dissolved in 40 mL of ethanol at 0 °C and for 1 h. Compound 3 (4 g,
0.016 mol) in 20 mL of ethanol was added to solution, and the
resulting mixture was stirred at RT for 30 min. The resulting mixture
was added slowly to a solution of KOH (2.73 g, 0.048 mmol) in 20 mL
of ethanol−H2O (20:1 v/v) at RT. The mixture was refluxed for 2 h at
90 °C. The reaction mixture was then poured into water and extracted
with ethyl acetate. After drying over anhydrous MgSO4, the solvent
was evaporated. The mixture and p-toluenesulfonic acid monohydrate
(0.1 g, 0.5 mmol) in 100 mL of hexane was refluxed for 1 h. After
cooling, the mixture poured into water (100 mL) and extracted with
ethyl acetate. The extract was successively washed with water, 5%
sodium hydrogen carbonate aqueous solution, and brine. After drying
over anhydrous MgSO4, the solvent was evaporated and the residue
was purified by column chromatography on silica gel with hexane as
eluent. After drying, the product was obtained as yellow oil. Yield: 1.9
3,3″-(3′,7′-Dimethyoctyl)-2,2′:5,2″-terselenophene (10). The
compound was synthesized using the same method as for compound
9, using tris(dibenzylideneacetone)dipalladium(0) (0.15 g, 0.16
mmol), tri-o-tolyphosphine (0.087 g, 0.28 mmol), compound 8 (1.1
g, 2.39 mmol), and compound 6 (1.84 g, 5.26 mmol) was dissolved in
40 mL of anhydrous toluene under N2. The solution was heated at 90
°C for 3 h. The mixture was then poured into water and extracted with
ethyl acetate. The extract was the successively washed with water and
brine. After drying over anhydrous MgSO4, the solvent was evaporated
and the residue was purified by column chromatography on silica gel
with hexane as eluent. After drying, the product was obtained as a
1
yellow solid. Yield: 1.2 g (82%). Fab-MS: m/z = 670. H NMR (300
MHz, CDCl3, δ): 7.88 (d, 2H), 7.21 (d, 2H), 7.14(s, 2H), 2.60 (m.
4H), 1.13−1.68 (m. 20H), 0.91 (d, 6H), 0.87 (d, 12H). 13C NMR (80
MHz, CDCl3, δ): 143.65, 141.41, 137.44, 133.75, 128.87, 128.83,
39.53, 38.24, 37.35, 33.15, 28.45, 24.96, 22.94, 22.85, 19.86. Anal.
Calcd for C32H48Se3: C 57.40, H 7.23. Found: C 57.35, H 7.23.
5,5″-Bis(trimethylstannyl)-3,3″-di(3′,7′-dimethyoctyl)-
2,2′:5,2″-terthiophene (11). To a solution of compound 9 (0.9 g,
1.7 mmol) in THF (15 mL), a 1.6 M solution of n-BuLi in hexane
(2.23 mL, 3.5 mmol) was added, and the mixture was stirred at −78
°C and for 1 h and then 1.0 M solution of trimethyltin chloride (3.5
mL, 3.5 mmol) was added in one portion. The solution was warmed to
room temperature and stirred at room temperature for 1 h. The
reaction mixture was then poured into water and extracted with ethyl
acetate. After drying over anhydrous MgSO4, the solvent was
evaporated. The crude product was washed several times by using
acetone/methanol (1/10) mixed solvents. The product was dissolved
in small amount of CHCl3 and precipitated in methanol at low
1
g (43%). Fab-MS: m/z = 273. H NMR (300 MHz, CDCl3, δ): 7.89
(d, 1H), 7.52 (s, 1H), 7.19 (d, 1H), 2.60 (m. 2H), 1.1−1.50 (m. 10H),
0.91 (d, 3H), 0.87 (d, 6H). 13C NMR (80 MHz, CDCl3, δ): 145.66,
131.66, 129.86, 39.54, 37.85, 37.35, 32.69, 29.70, 28.19, 24.91, 22.93,
22.84, 19.80. Anal. Calcd for C14H24S: C 61.98, H 8.92. Found: C
61.87, H 8.90.
2-Bromo-3-(3′,7′-dimethyoctyl)thiophene (5). To a stirred
solution of compound 1 (3.1 g, 13.8 mmol) in chloroform−acetic acid
(1:1 v/v, 150 mL), N-bromosuccinimide (NBS) (2.73 g, 15.3 mmol)
was added. The mixture was stirred at 0 °C for 1 h and then poured
into water (100 mL) and extracted with ethyl acetate. The extract was
successively washed with water, 5% sodium hydrogen carbonate
aqueous solution, and brine. After drying over anhydrous MgSO4, the
solvent was evaporated and the residue was purified by column
chromatography on silica gel with hexane as eluent. After drying, the
product was obtained as yellow oil. Yield: 4.00 g (95%). Fab-MS: m/z
1
temperature (−40 °C). Yield: 0.6 g (40%). Fab-MS: m/z = 854. H
NMR (300 MHz, CDCl3, δ): 7.04 (s, 2H), 6.99 (s, 2H), 2.76 (t. 4H),
1.18−1.69 (m, 20H), 0.91 (d, 6H), 0.87 (t, 12H), 0.37 (s, 18H). 13C
NMR (80 MHz, CDCl3, δ): 141.11, 139.98, 138.55, 136.68, 130.22,
126.29, 39.54, 38.21, 37.36, 33.23, 28.20, 27.19, 24.98, 22.84, 19.87,
−8.02. Anal. Calcd for C38H64S3Sn2: C 53.41, H 7.15, S 11.26. Found:
C 53.51, H 7.20, S 11.34.
1
= 303. H NMR (300 MHz, CDCl3, δ): 7.16 (d, 1H), 6.79 (d, 1H),
2.60 (m. 2H), 1.12−1.54 (m. 10H), 0.91 (d, 3H), 0.87 (d, 6H). 13C
NMR (80 MHz, CDCl3, δ): 143.64, 128.49, 125.26, 108.88, 39.53,
37.24, 37.11, 32.68, 28.20, 27.28, 24.90, 22.93, 22.85, 19.80. Anal.
Calcd for C14H23BrS: C 55.44, H 7.64, S 10.50. Found: C 55.41, H
7.70, S 10.50.
5,5″-Bis(trimethylstannyl)-3,3″-di(3′,7′-dimethyoctyl)-
2,2′:5,2″-terselenophene (12). The compound was synthesized
using the same method as for compound 11; using compound 6 (0.7
g, 1 mmol) in THF (15 mL), a 1.6 M solution of n-BuLi in hexane
(1.3 mL, 2 mmol) was added, and the mixture was stirred at −78 °C
and for 1 h and then 1.0 M solution of trimethyltin chloride (2.1 mL,
2.1 mmol) was added in one portion. The solution was warmed to
room temperature and stirred at room temperature for 1 h. The
reaction mixture was then poured into water and extracted with ethyl
acetate. After drying over anhydrous MgSO4, the solvent was
evaporated. The crude product was washed several times by using
acetone/methanol (1/10) mixed solvents. The product was dissolved
in small amount of CHCl3 and precipitated in methanol at low
2-Bromo-3-(3′,7′-dimethyoctyl)selenophene (6). The com-
pound was synthesized using the same method as for compound 5;
using compound 3 (1.9 g, 7 mmol) in chloroform−acetic acid (1:1 v/
v, 50 mL), N-bromosuccinimide (NBS) (1.32 g, 7.2 mmol) was added.
The mixture was stirred at 0 °C for 1 h and then poured into water
(100 mL) and extracted with ethyl acetate. The extract was
successively washed with water, 5% sodium hydrogen carbonate
aqueous solution, and brine. After drying over anhydrous MgSO4, the
solvent was evaporated and the residue was purified by column
chromatography on silica gel with hexane as eluent. After drying, the
product was obtained as yellow oil. Yield: 2.35 g (96%). Fab-MS: m/z
1
= 351. H NMR (300 MHz, CDCl3, δ): 7.86 (d, 1H), 7.05 (d, 1H),
1
2.60 (m. 2H), 1.2−1.60 (m. 10H), 0.91 (d, 3H), 0.87 (d, 6H). 13C
NMR (80 MHz, CDCl3, δ): 144.64, 131.35, 130.28, 111.20, 39.52,
37.22, 36.98, 32.70, 28.55, 28.19, 24.89, 22.94, 22.86, 19.82. Anal.
Calcd for C14H23BrSe: C 48.02, H 6.62. Found: C 47.96, H 6.62.
3,3″-(3′,7′-Dimethyoctyl)-2,2′:5,2″-terthiophene (9). A solu-
tion tris(dibenzylideneacetone)dipalladium (0) (0.15 g, 0.16 mmol),
tri-o-tolyphosphine (0.087 g, 0.28 mmol), compound 7 (0.98 g, 2.4
mmol), and compound 5 (1.52 g, 5.01 mmol) was dissolved in 40 mL
of anhydrous toluene under N2. The solution was heated at 90 °C for
3 h. The mixture was then poured into water and extracted with ethyl
acetate. The extract was the successively washed with water and brine.
After drying over anhydrous MgSO4, the solvent was evaporated and
the residue was purified by column chromatography on silica gel with
hexane as eluent. After drying, the product was obtained as a yellow
temperature (−60 °C). Yield: 0.41 g (52%). Fab-MS: m/z = 996. H
NMR (300 MHz, CDCl3, δ): 7.37 (s, 2H), 6.81 (s, 2H), 2.73 (t. 4H),
1.18−1.69 (m, 20H), 0.91 (d, 6H), 0.87 (t, 12H), 0.36 (s, 18H). 13C
NMR (80 MHz, CDCl3, δ): 144.01, 143.76, 143.44, 141.28, 133.73,
128.90, 39.54, 38.24, 37.36, 33.16, 28.38, 28.20, 24.98, 22.86, 19.87,
−7.69. Anal. Calcd for C38H64Se3Sn2: C 45.86, H 6.48. Found: C
45.90, H 6.50.
P3TDTQ. A 100 mL Schlenk flask containing anhydrous
chlorobenzene (10 mL), compound 11 (0.17 g, 0.2 mmol), compound
12 (0.18 g, 0.2 mmol), tris(dibenzylideneacetone)dipalladium(0)
(0.01 g, 0.01 mmol), and tri(o-tolyl)phosphine (6 mg, 0.02 mmol)
was kept under a nitrogen atmosphere at 130 °C for 72 h. When the
reaction had finished, reaction mixture was precipitated from the 10
mL of HCl and 150 mL of methanol. The polymer was dissolved in
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small amount of CHCl3 and precipitated in methanol. The resulting
polymer was further purified by Soxhlet extraction using methanol and
hexane then dried in vacuum to give dark-green solid. Yield: 0.2 g
spin-coated onto each ITO anode from a solution purchased from
H.C. Starck and baked for 20 min at 140 °C in a glovebox. Each
polymer:PC61BM solution was then spin-coated onto the PEDOT:PSS
layer. The polymer solution for spin-coating was prepared by
dissolving the polymer (1 wt %) in chlorobenzene. Preannealing was
not carried out. LiF and aluminum contacts were formed by vacuum
deposition at pressures below 3 × 10−6 Torr, providing an active area
of 0.09 cm2. Solar cell efficiencies were characterized under simulated
100 mW/cm2 AM 1.5G irradiation from a Xe arc lamp with an AM 1.5
global filter. Simulator irradiance was characterized using a calibrated
spectrometer, and the illumination intensity was set using an NREL
certified silicon diode with an integrated KG1 optical filter. The EQE
was measured by underfilling the device are a using a reflective
microscope objective to focus the light output from a 100 W halogen
lamp outfitted with a monochromator and optical chopper; the
photocurrent was measured using a lock-in amplifier, and the absolute
photon flux was determined using a calibrated silicon photodiode. All
device fabrication procedures and measurements were carried out in
air at room temperature.
1
(77%). H NMR (300 MHz, CDCl3, δ): 8.08 (br, 2H) 7.81 (br, 6H)
7.12 (br, 6H) 6.92 (br, 6H), 4.04 (br, 4H), 2.80 (br, 4H) 1.24−0.81
(m, 76H). Anal. Calcd for C79H100N2O2S5: C 70.81, H 8.24, N 2.66, O
3.04, S 15.24. Found: C 70.72, H 8.28, N 2.66, O 3.27, S 15.21.
P3SDTQ. The compound was synthesized using the same method
as for P3TDTQ, with compound 12 (0.2 g, 0.2 mmol), compound 13
(0.18 g, 0.2 mmol), tris(dibenzylideneacetone)dipalladium(0) (0.01 g,
0.01 mmol), tri(o-tolyl)phosphine (6 mg, 0.02 mmol), and
chlorobenzene (10 mL) being kept under a nitrogen atmosphere at
130 °C for 72 h. When the reaction had finished, reaction mixture was
precipitated from the 10 mL of HCl and 150 mL of methanol. The
polymer was dissolved in small amount of CHCl3 and precipitated in
methanol. The resulting polymer was further purified by Soxhlet
extraction using methanol and hexane then dried in vacuum to give
dark-green solid. Yield: 0.17 g (80%). 1H NMR (300 MHz, CDCl3, δ):
8.09 (br, 2H) 7.81(br, 6H) 7.19 (br, 6H) 6.92 (br, 6H), 4.08 (br, 4H),
2.82 (br, 4H) 1.55−0.81 (m, 76H). Anal. Calcd for
C79H100N2O2S2Se3: C 67.26, H 7.15, N 1.99, O 2.27, S 4.55. Found:
C 67.19, H 7.29, N 1.84, O 2.45, S 4.16.
ASSOCIATED CONTENT
■
S
* Supporting Information
P3TDTDPP. The compound was synthesized using the same
method as for P3TDTQ, with compound 11 (0.17 g, 0.2 mmol),
compound 14 (0.136 g, 0.2 mmol), tris(dibenzylideneacetone)-
dipalladium(0) (0.01 g, 0.01 mmol), tri(o-tolyl)phosphine (6 mg,
0.02 mmol), and chlorobenzene (10 mL) being kept under a nitrogen
atmosphere at 130 °C for 72 h. When the reaction had finished,
reaction mixture was precipitated from the 10 mL of HCl and 150 mL
of methanol. The polymer was dissolved in a small amount of CHCl3
and precipitated in methanol. The resulting polymer was further
purified by Soxhlet extraction using methanol and hexane then dried in
IV characteristics and AFM images of the polymers. This
material is available free of charge via the Internet at http://
pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: inamkang@catholic.ac.kr.
1
vacuum to give dark solid. Yield: 0.17 g (62%). H NMR (300 MHz,
ACKNOWLEDGMENTS
CDCl3, δ): 8.98−8.90 (br, 2H), 7.18−6.92 (br, 6H), 4.03 (br, 4H)
2.77 (br, 4H) 1.92−0.86 (m, 68H). Anal. Calcd for C79H100N2O2S5: C
74.72, H 8.15, N 2.18, O 2.49, S 12.47. Found: C 74.35, H 8.04, N
2.44, O 2.37, S 12.84.
■
This research was supported by Basic Science Research
Program through the National Research Foundation of Korea
(NRF) funded by the Ministry of Education, Science and
Technology (2011-0004016), also supported by the New &
Renewable Energy of the Korea Institute of Energy Technology
Evaluation and Planning (KETEP) grant funded by the Korea
government Ministry of Knowledge Economy
(2011T100200034), and by a grant from the cooperative
R&D Program (B551179-08-03-00) funded by the Korea
Research Council Industrial Science and Technology, Republic
of Korea
P3SDTDPP. The compound was synthesized using the same
method as for P3TDTQ, with compound 12 (0.2 g, 0.2 mmol),
compound 14 (0.136 g, 0.2 mmol), tris(dibenzylideneacetone)-
dipalladium(0) (0.01 g, 0.01 mmol), tri(o-tolyl)phosphine (6 mg,
0.02 mmol), and chlorobenzene (10 mL) being kept under a nitrogen
atmosphere at 130 °C for 72 h. When the reaction had finished,
reaction mixture was precipitated from the 10 mL of HCl and 150 mL
of methanol. The polymer was dissolved in small amount of CHCl3
and precipitated in methanol. The resulting polymer was further
purified by Soxhlet extraction using methanol and hexane and then
1
dried in a vacuum to give a dark solid. Yield: 0.13 g (54%). H NMR
REFERENCES
■
(300 MHz, CDCl3, δ): 8.96−8.89 (br, 2H), 7.82−6.82 (br, 6H), 4.02
(br, 4H) 2.69 (br, 4H) 1.91−0.87 (m, 68H). Anal. Calcd for
C62H86N2O2S2Se3: C 62.45, H 7.25, N 2.35, O 2.68, S 5.38. Found: C
62.26, H 7.28, N 2.21, O 2.91, S 5.18.
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