Direct Arylation Polycondensation of Bithiazole Derivatives with

Oct 24, 2014 - Novel π-conjugated polymers with a bithiazole unit and various acceptor units were synthesized by polycondensation via Pd-catalyzed di...
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Direct Arylation Polycondensation of Bithiazole Derivatives with Various Acceptors Masahiro Kuramochi, Junpei Kuwabara,* Wei Lu, and Takaki Kanbara* Tsukuba Research Center for Interdisciplinary Materials Science (TIMS), Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8573, Japan S Supporting Information *

ABSTRACT: Novel π-conjugated polymers with a bithiazole unit and various acceptor units were synthesized by polycondensation via Pd-catalyzed direct arylation. The results of polycondensation reactions depend on chalcogen elements in the monomers. The presence of a Se atom inhibited polymerization, presumably owing to the coordination of the Se moiety to the Pd center; the issue was resolved by increasing the reaction temperature (120 °C). The chalcogen elements also affected the interchain interactions of the obtained polymers. The strong interchain interactions led to low solubility, high crystallinity, and a large red-shift of absorption in the film state compared with that in the solution state. Absorption spectra and DFT calculations revealed that the bithiazole units served as weak donor units in case that the bithiazole units were directly connected to strong acceptor units. The combination of the bithiazole units with the strong acceptor units afforded deep HOMO−LUMO levels.

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INTRODUCTION π-Conjugated polymers have been extensively investigated as materials for organic photovoltaic (OPV) cells,1 organic lightemitting diodes,2 and organic field-effect transistors (OFETs).3 In particular, thiophene-based polymers such as poly(3hexylthiophene-2,5-diyl) are regarded as polymer materials suitable for organic electronic devices owing to their high carrier mobility and strong light-harvesting properties.4 One of the well-known thiophene analogues is thiazole, which has a N atom at the 3-position instead of a C−H moiety as in thiophene. In thiazole-based conjugated polymers, the lack of the C−H bond leads to low steric hindrance between the repeating units, which provides planar structures.5 Thiazolebased polymers tend to have strong interchain interactions and high crystallinities because of their planar structures and intermolecular S···S and S···N interactions.6 Thiazole is more electron deficient than thiophene; therefore, the displacement of a thiophene unit to a thiazole unit in a polymer structure provided excellent air stability in OFETs owing to the low highest occupied molecular orbital (HOMO) level.5b,7 Because of these attractive features of the thiazole unit, thiazole-based polymers have been investigated for application as OPV8 and OFET materials.9 However, the examples of thiazole-based polymers are much fewer than those of thiophene-based polymers, and there is room for further investigation. One of the bottlenecks for investigation of thiazole-based polymers is the difficulty of synthesizing a high-molecular-weight polymer because of the instability of monomers and the low solubility of polymers.5b,8b−d,l,10 For the development of thiazole-based polymers, it is essential to develop an efficient synthetic method © 2014 American Chemical Society

and obtain new insights for improving their solubility without loss of their attractive features. Thiazole-based polymers have been synthesized primarily by cross-coupling reactions such as the Suzuki−Miyaura coupling and the Migita−Kosugi−Stille coupling reactions.8−10 However, instability of the stannylated bithiazole monomer resulted in low molecular weights of the obtained polymers.8f,l Alternatively, polycondensation using catalytic dehydrohalogenative cross-coupling reactions,11 socalled direct arylation, has been developed recently as a new synthetic method for conjugated polymers.12−14 Because this polycondensation method does not require an organometallic monomer, the preparation step for a stannylated monomer and concern about its instability can be avoided. The absence of organometallic monomers also provides high purity of the polymers owing to no contamination of metal-containing waste from organometallic monomers.13e,14e Because the C−H bonds in thiazole have high reactivity for direct arylation,11b polycondensation via the direct arylation reaction of 4,4′dinonyl-2,2′-bithiazole with dibromoarylenes such as 2,7dibromo-9,9-dioctylfluorene yielded the corresponding conjugated polymers.14c,d Herein, we report further investigation of direct arylation polycondensation of the bithiazole monomer to establish a reliable synthetic method for thiazole-based polymers. In particular, dibromoarylenes having strong electron-accepting properties were chosen as coupling partners for assessing structure−property relationships of the electronReceived: July 12, 2014 Revised: August 28, 2014 Published: October 24, 2014 7378

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Scheme 1. Synthesis of P1−P5

Table 1. Synthesis of P1−P5a entry

polymer

temp (°C)

time (h)

conc (M)

Mnb

Mw/Mnb

yieldc

1 2 3 4 5 6 7 8 9

P1

100 80 100 100 100 120 100 100 100

3 48 24 3 3 24 3 6 3

0.3 0.15 0.1 0.3 0.3 0.3 0.3 0.3 0.3

9400 13400 (13700)e 49500 5000 1100 20600 12400 16300 9600

1.35 1.81 (4.85)e 2.23 1.23 2.08 2.35 1.47 2.74 1.96

54d 55d 83 29d 22 84d 68 88 82

P1′ P2 P3 P4 P5

a

Reactions were carried out using Pd(OAc)2 (2 mol %), pivalic acid (30 mol %), and K2CO3 (2.5 equiv) in DMAc. bEstimated by GPC calibrated on polystyrene standards. cThe products were obtained by reprecipitation from CHCl3−CH3OH. dProducts insoluble in CHCl3 were also obtained. e Estimated by high-temperature GPC using o-dichlorobenzene as an eluent at 140 °C.

weight to that by the standard measurement (entry 2), overestimation of molecular weight by aggregation is considered to be small in this case. The yield of the polymer was not improved owing to formation of a CHCl3-insoluble product. Direct arylation polycondensation sometimes afforded insoluble products owing to cross-linking structures that were caused by side reactions at the undesired C−H bonds.12,14 Therefore, the structure of the CHCl3-insoluble fraction in entry 2 was investigated by NMR and mass spectroscopy. The fraction was soluble in 1,1,2,2-tetrachloroethane-d4 at 100 °C and its 1H NMR spectrum exhibited no branching or crosslinking structures (Figure 1). The MALDI-TOF-MASS spectrum also supported this result (Figure S22). On the basis of these results, we concluded that the CHCl3-insoluble fraction was not formed by a cross-linking reaction. The low solubility of P1 was considered to be caused by strong interchain interaction. The bithiazole unit is likely to play an important role in the strong interaction because a similar polymer with a bithiophene−benzothiadiazole structure (P0, Figure 2) was found to be soluble in CHCl3 even with its high molecular weight (Mn = 31 300).15 To elucidate the effects of alkyl chains on solubility,16 bithiazole with 2-ocyldodecyl chains was synthesized and used as a monomer (Scheme 1). The

deficient polymers in terms of interchain interactions and optical properties.

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RESULTS AND DISCUSSION Optimization of Polymerization Conditions. We previously reported that the polycondensation reaction of 4,4′-dinonyl-2,2′-bithiazole with 2,7-dibromo-9,9-dioctylfluorene in the presence of Pd(OAc)2 (2 mol %), pivalic acid (PivOH, 30 mol %), and K2CO3 (2.5 equiv) in dimethylacetamide (DMAc, 0.3 M) for 3 h at 100 °C produced the corresponding polymer with a molecular weight of 46 000 in 90% yield.14c The investigation of the polycondensation of 4,4′dinonyl-2,2′-bithiazole with 4,7-dibromobenzothiadiazole began with the reported conditions (Scheme 1). The reaction afforded poly[(4,4′-dinonyl-2,2′-bithiazole-5,5′-diyl)-(benzothiadiazole-4,7-diyl)] (P1) in 54% yield as a CHCl3-soluble fraction (Table 1, entry 1). The moderate yield was caused by the formation of a CHCl3-insoluble product. Examination of reaction conditions such as reaction temperature, time, and concentration afforded somewhat higher molecular weight (entry 2 and Table S1 in Supporting Information). Because a high-temperature GPC measurement shows similar molecular 7379

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contribute to the strong interchain interaction, leading to low solubility. In the synthesis of P4, a reaction time of 3 h gave a product with a moderate molecular weight and yield without formation of CHCl3-insoluble products (entry 7). The prolonged reaction time provided the increases of the molecular weight and yield of the polymer (entry 8). P5 was obtained under the standard conditions (3 h, 100 °C) in a good yield (entry 9). X-ray Diffraction Study. To gain information about the morphologies of the products in the film state, an X-ray diffraction (XRD) study was conducted on P1−P5. Figure 3

Figure 1. 1H NMR spectrum of the CHCl3-insoluble fraction of P1 (Table 1, entry 2) (600 MHz, C2D2Cl4, 373 K).

Figure 3. X-ray diffraction patterns of P1−P5. Figure 2. Structure of the reference polymer.

shows the XRD patterns of the drop-cast films of P1−P5 without annealing. All polymer films exhibited diffraction peaks around 5° which are caused by lamellar spacing (Table S3).20 The chalcogen atoms in P1−P3 strongly affected the crystallinity of the polymer films; the sharpness of the diffraction peaks is arranged in the order of P2 (O), P1 (S), and P3 (Se). In addition, secondary diffraction peaks are observed for P2 (sharp) and P1 (broad). The trend in the crystallinities of P1−P3 is well correlated with the strength of the interchain interaction discussed above. The polymer with branching alkyl chains on the bithiazole unit (P1′) exhibited a broad diffraction peak presumably due to the weakened interaction by steric hindrance of the branching alkyl chains. In contrast to the clear diffraction peaks from the lamellar structures, diffraction from a π−π stacking structure was not clearly observed around 24°. Optical Properties. Figure 4 shows absorption spectra of P1−P5 in solution and in the thin film state. These absorption properties and the optical bandgaps are summarized in Table 2. The maximum absorption wavelength of P1 in the solution state was 468 nm. The introduction of the strong acceptor unit resulted in absorption in a longer wavelength region than in the case of the bithiazole-based polymer with the fluorene unit (417 nm).14c These observations suggest that the bithiazole unit serves as the donor, and intramolecular charge transfer to the strong acceptor, benzothiadiazole, can be observed in the absorption spectrum. The details of the assignments will be discussed in the section that describes the theoretical calculations. The absorption patterns for the thin film state exhibit red-shifts compared with the solution state. The degree of red-shift strongly depends on the structure of the polymers; P1 and P2 exhibit particularly large red-shifts (78 and 74 nm). The large red-shifts are consistent with the above-mentioned strong interchain interaction and high crystallinity. Because the

reaction afforded the corresponding polymer (P1′) with a high molecular weight (Mn = 49 500) in 83% yield (entry 3) without formation of a CHCl3-insoluble fraction. This result also provides evidence that the side reaction scarcely occurred at the undesired C−H bond. The polycondensation of 4,4′-dinonyl2,2′-bithiazole with 4,7-dibromobenzoxadiazole afforded P2 in 29% yield as a CHCl3-soluble fraction (entry 4). The yield of P2 was lower than that of P1 because most of the polymeric products were insoluble in CHCl3, suggesting low solubility of P2. In this reaction, precipitation occurred at the early stage of the polymerization. Therefore, C−C bond formation was likely to proceed smoothly. In contrast, the reaction with 4,7dibromobenzoselenadiazole proceeded with difficulty; the reaction afforded a low-molecular-weight polymer (Mn = 1100) in low yield (22%), and the products were mostly hexane-soluble (entry 5). The reaction at a higher temperature (120 °C) and a long reaction time (48 h) improved the molecular weight and the yield of P3 (entry 6). The coordinating property of a Se atom to a Pd center may inhibit the catalytic reaction at low temperatures. Similarly, Leclerc et al. reported that direct arylation polycondensation of selenopheno[3,4-c]pyrrole-4,6-dione did not afford polymeric products.17 Interestingly, there are large differences in the solubilities of P1−P3 although only chalcogen elements vary in the structures. These differences should be induced by interchain interactions of the polymers. Among the acceptor units in P1−P3, benzoxadiazole is the strongest,18 and it provides strong polarization in the main chain and leads to strong electrostatic interaction between the polymer chains. In addition, theoretical calculations revealed that an intermolecular S···O interaction was the strongest in the S···chalcogen interactions.19 The intermolecular S···O interaction may also 7380

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red-shift of P0 in the film state is only 43 nm, the bithiazole unit is considered to provide the characteristic red-shift and high crystallinity.15 P1 and P1′, which have a common main chain, show similar absorption spectra in solution, but a large difference was observed in the film state. The branching alkyl chains are likely to have weakened the interchain interaction. DFT Calculations. To understand the electronic structures and optical properties of the polymers, density-functional theory (DFT) calculations were performed on model compounds for the repeating units of P1−P5 at the B3LYP/ 6-31G(d) level. The alkyl chains were replaced by ethyl groups in order to simplify the calculations. Figure 5 exhibits energyminimized structures of the model compounds and the corresponding HOMO and LUMO distributions for P1, P4, and P5. It should be noted that the dihedral angles between the thiazole moieties in the bithiazole units are 0.06°. The planar structure is a characteristic of the bithiazole unit because the corresponding dihedral angle of the bithiophene unit is 13.14° on average (Figure S1). In the molecular orbital of P1, the HOMO is delocalized over all units whereas the LUMO is localized on the benzothiadiazole unit. Similar distributions of the HOMO and LUMO were reported for a thiophene− benzothiadiazole−thiophene trimer.18 Time-dependent DFT calculations revealed that the absorption at 468 nm in P1 could be assigned to the transition from the HOMO to the LUMO (Table S2). The contribution of the bithiazole unit to the HOMO and the predominant contribution of the benzothiadiazole unit to the LUMO show that the absorption can be categorized into intramolecular charge transfer from the bithiazole to the benzothiadiazole units. A similar trend was observed for P2 and P3 (Figure S1). These results support the above-mentioned discussion that the bithiazole units serve as donor units owing to their direct connections to the stronger acceptors, although a bithiazole unit is normally regarded as an acceptor unit in a conjugated polymer.8 In the model compounds for P4 and P5, the LUMOs are delocalized over all units as contrasted with the localized LUMOs of P1−P3. The delocalized LUMOs of P4 and P5 indicate similar

Figure 4. UV−vis absorption spectra of P1−P5 (a) in CHCl3 (1.0 × 10−5 M) and (b) in the film state.

Table 2. Optical Properties and Energy Levels of Polymers absorption properties

energy levels

polymer

λmax (nm)

λmax (nm)

λonset (nm)

Egopt d (eV)

EHOMOe (eV)

ELUMOf (eV)

P1 P1′ P2 P3 P4 P5

468 463 474 485 436 418

546 496 548 524 473 422

623 569 629 616 530 472

1.99 2.18 1.97 2.01 2.34 2.63

−5.61 −5.62 −5.96 −5.71 −5.39 −5.99

−3.62 −3.44 −3.99 −3.70 −3.05 −3.36

a

b

b,c

In CHCl3. bIn the thin film state. cAbsorption onset. dOptical bandgap from the absorption edge. eThe value of EHOMO was obtained from the ionization potential. fELUMO = EHOMO + Egopt. a

Figure 5. Energy-minimized structures of the model compounds for P1, P4, and P5 obtained by DFT. 7381

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unit. The bithiazole unit served as a weak donor unit by direct connection to a stronger acceptor unit, although bithiazole units are normally regarded as acceptor units. The combination of weak donor and strong acceptor units afforded deep HOMO−LUMO levels and strong interchain interaction based on electrostatic interaction. These findings contribute to the establishment of rational designs for n-type semiconducting polymers and provide a simple synthetic procedure.

accepting properties of benzotriazole and quinoxaline units to the bithiazole unit. The decreased acceptor strengths of the benzotriazole and quinoxaline units were also reported in the literature.18 The dihedral angles between the bithiazole and quinoxaline units in P5 (42.23° and 42.22°) were larger than the corresponding angles in P1 (39.37° and 39.36°), presumably owing to the steric hindrance of the six-membered ring of the quinoxaline unit (Figure 5). Because P5 shows a small red-shift of absorption in the film state compared with that in the solution state, these dihedral angles play important roles in interchain interaction. Energy Levels. Figure 6 shows the energy levels for P1− P5, which were obtained from the ionization potential and

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EXPERIMENTAL SECTION

Materials. 4,7-Dibromo-2,1,3-benzothiadiazole, 4,7-dibromo-2,1,3benzoselenadiazole, Pd(OAc)2, pivalic acid, K2CO3, and other chemicals were received from commercial suppliers and used without further purification. Anhydrous dimethylacetamide (DMAc) was purchased from Kanto Chemical and used as a dry solvent. 4,4′Dinonyl-2,2′-bithiazole,8a 4,7-dibromo-2,1,3-benzoxadiazole,23,24 4,7dibromo-2-(2-ethylhexyl)-2H-benzotriazole,25 and 1-bromo-2-octyldodecane26 were prepared according to the literature methods. 4,4′Dinonyl-2,2′-bithiazole in highly pure form was obtained as needleshaped crystals by further purification through medium pressure liquid chromatography (MPLC) and crystallization. General Methods. NMR spectra were recorded on Bruker AVANCE-400 and AVANCE-600 NMR spectrometers. Gel permeation chromatography (GPC) measurements were carried out on a SHIMADZU prominence GPC system equipped with polystyrene gel columns using CHCl3 as an eluent at 40 °C after calibration with polystyrene standards. A high-temperature GPC measurements were carried out on a Waters alliance GPC 2000 equipped with polystyrene gel columns using o-dichlorobenzene as an eluent at 140 °C after calibration with polystyrene standards. MALDI-TOF-MS spectra were recorded on AB SCIEX MALDI TOF/TOF 5800 using dithranol as a matrix. All manipulations for the reactions were carried out under a nitrogen atmosphere using a standard Schlenk technique. Column chromatography was carried out with silica gel 60 (Kanto, 40−100 μm, neutral). Purification by MPLC was carried out on a YAMAZEN FR50N using EtOAc/hexane (1:50 v/v) as an eluent. Purifications by high performance liquid chromatography (HPLC) were carried out on a JAI LC-9201 using CHCl3 as an eluent. XRD experiments were performed with a Philips X’Pert PRO X-ray diffractometer and with Cu Kα radiation (λ = 1.542 Å) at a generator voltage of 45 kV and a current of 40 mA. Differential scanning calorimetry (DSC) and thermogravimetric differential thermal analysis (TG-DTA) measurements were carried out using X-DSC7000 and TG/DTA7300 systems from Seiko Instruments Inc., respectively. UV−vis absorption spectra were obtained using a V-630 spectrophotometer. The HOMO energy levels were estimated by photoelectron yield spectroscopy using an AC-3 spectrometer (Riken Keiki). DFT calculations were performed at the B3LYP/6-31G(d) level with the Gaussian09 Rev. D.01 program.27 Synthetic Procedures. 4-Octyltetradodecane-2-one.28 To a 100 mL round-bottom flask under nitrogen was added magnesium (566 mg, 23 mmol) and anhydrous diethyl ether (14.4 mL) and a piece of iodide. After the mixture was well stirred at room temperature, 1bromo-2-octyldodecane (7.0 g, 19 mmol) in anhydrous diethyl ether (5.0 mL) was added dropwise. The reaction mixture was stirred overnight for preparation of the corresponding Grignard reagent. To another 100 mL round-bottom flask under nitrogen was added anhydrous diethyl ether (20 mL) and acetic anhydride (9.3 mL, 97 mmol). After the mixture was cooled to −70 °C, the solution of the prepared Grignard reagent was added to the mixture in a dropwise manner. The mixture was stirred for 2 h at −70 °C before warming up to room temperature. The mixture was treated with an aqueous solution of ammonium chloride. The organic materials were extracted with diethyl ether and then dried over sodium sulfate. After evaporation of volatiles, the residue was purified by flash column chromatography on silica gel (eluent: CHCl3/hexane (1:1 v/v)). The product was obtained as a colorless oil in 26% yield. 1H NMR (400 MHz, CDCl3): δ 2.33 (d, J = 6.8 Hz, 2H), 2.13 (s, 3H), 1.95−1.84 (m, 1H), 1.31−1.25 (m, 32H), 0.88 (t, J = 7.0 Hz, 6H). 13C{1H} NMR

Figure 6. Energy levels of P1−P5.

optical bandgap (Table 2). The HOMO and LUMO levels of P1 (−5.61 and −3.62 eV) are lower than those of the reference polymer P0 (−5.46 and −3.35 eV).15 It is surmised that the weak donor strength of bithiazole results in the low HOMO− LUMO level. In a general donor−acceptor polymer, the LUMO level is mainly affected by the strength of the acceptor unit.1 The order of the LUMO levels is P2 < P3 < P1 < P5 < P4, which is consistent with the acceptor strength18 of the introduced units. The deep LUMO level of P2 is close to that of a promising n-type semiconducting polymer.21 Thermal Analysis. Thermal gravimetric analysis (TGA) of the polymers was conducted under an Ar atmosphere (Figure S28 and Table S4). All polymers showed high 5% weight-loss temperatures (>320 °C). The high thermal tolerances are sufficient for application to organic optoelectronic devices. Differential scanning calorimetry (DSC) measurements revealed clear melting points only for P1′ and P4, presumably due to the branching alkyl chains. The polymer with a long alkyl chain (P1′) had a lower melting point than P4.22

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CONCLUSIONS Direct arylation polycondensation of bithiazole monomers with various acceptor units yielded six novel polymers. The presence of a Se atom in the monomer inhibited polymerization, presumably owing to the coordination of the Se moiety to the Pd center; the issue was resolved by increasing the reaction temperature. Strong acceptor units such as benzoxadiazole afforded strong interchain interaction, leading to low solubility. The introduction of a branching alkyl chain provided better solubility for that polymer, which led to a high molecular weight of 49 500. The evaluation of physical properties revealed that a bithiazole unit provided high planarity and crystallinity of the polymer on the basis of a comparison with a bithiophene 7382

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(150 MHz, CDCl3): δ 209.44, 48.90, 34.01, 34.00, 31.92, 31.90, 30.39, 29.93, 29.65, 29.63, 29.59, 29.34, 29.32, 26.62, 22.69, 22.67, 14.10 (5 signals of the alkyl group were overlapped). 1-Bromo-4-octyltetradodecane-2-one. Bromine (0.24 mL, 4.7 mmol) was added in a dropwise manner to a stirred solution of 4octyltetradodecane-2-one (1.5 g, 4.7 mmol) in methanol (7.2 mL) at −10 °C. The mixture was stirred for 1 h at 0 °C and then stirred for another 1 h at room temperature. Water (1.4 mL) and then concentrated sulfuric acid (2.5 mL) were added to the mixture in an ice bath. After the mixture was stirred overnight at room temperature, the organic materials were extracted with chloroform and then dried over sodium sulfate. After evaporation of volatiles, the residue was purified by flash column chromatography on silica gel (eluent: CHCl3/ hexane (1:4 v/v)). The product was obtained as a colorless oil in 74% yield. 1H NMR (400 MHz, CDCl3): δ 3.87 (s, 2H), 2.56 (d, J = 6.8 Hz, 2H), 1.99−1.88 (m, 1H), 1.35−1.15 (m, 32H), 0.88 (t, J = 6.8, 6H). 13C{1H} NMR (150 MHz, CDCl3): δ 202.16, 44.79, 34.76, 34.02, 33.90, 31.93, 31.90, 29.88, 29.65, 29.64, 29.62, 29.58, 29.35, 29.31, 26.62, 22.69, 22.68, 14.12 (4 signals of the alkyl group were overlapped). 4,4′-Di(2-octyldodecyl)-2,2′-bithiazole. 1-Bromo-4-octyltetradodecane-2-one (1.25 g, 3.1 mmol), dithiooxamide (176 mg, 1.5 mmol), and ethanol (7.4 mL) were placed in a 100 mL two-necked flask equipped with a reflux condenser. The solution was heated at refluxed temperature for 6 h. After cooling to room temperature, the mixture was poured onto the crushed ice. The organic materials were extracted with chloroform and then dried over sodium sulfate. After evaporation of the solvent, the residue was purified by flash column chromatography on silica gel (eluent: EtOAc/hexane (1:20 v/v)), MPLC, and HPLC. The product was obtained as a pale yellow oil in 63% yield. 1H NMR (600 MHz, CDCl3): δ 6.91 (s, 2H), 2.73 (d, J = 6.6, 4H), 1.91−1.79 (m, 2H), 1.36−1.17 (m, 64H), 0.93−0.82 (m, 12H). 13C{1H} NMR (150 MHz, CDCl3): δ 160.72, 158.16, 115.32, 37.71, 35.99, 33.35, 31.95, 31.93, 30.04, 29.71, 29.68, 29.63, 29.38, 29.36, 26.51, 22.71, 14.13 (6 signals of the alkyl group were overlapped). Anal. Calcd for C46H84N2S2: C, 75.76; H, 11.61; N, 3.84. Found: C, 75.53; H, 11.88; N, 3.78. Calcd mass for C46H85N2S2 (M + 1): 729.6. Found: 729.7. Poly[(4,4′-dinonyl-2,2′-bithiazole-5,5′-diyl)-(2,1,3-benzothiadiazole-4,7-diyl)] (P1). A mixture of Pd(OAc)2 (1.12 mg, 0.0050 mmol), pivalic acid (0.0085 mL, 0.075 mmol), K2CO3 (86.4 mg, 0.63 mmol), 4,7-dibromo-2,1,3-benzothiadiazole (73.5 mg, 0.25 mmol), and 4,4′dinonyl-2,2′-bithiazole (105 mg, 0.25 mmol) was stirred in anhydrous DMAc (1.67 mL) for 48 h at 80 °C under a nitrogen atmosphere. After cooling to room temperature, the mixture was poured into aqueous solution of ethylenediaminetetraacetic acid disodium salt (pH = 8). The suspension was stirred for 1 h at room temperature. The precipitates were separated by filtration and washed with 10% HCl solution, distilled water, methanol, and hexane. The black solid was extracted with CHCl3 (100 mL) by sonication and stirring at room temperature, and the CHCl3-insoluble fraction was separated by filtration. The solution of the CHCl3-soluble fraction was concentrated and reprecipitated into methanol. The black-green solid of P1 was collected by filtration and dried under reduced pressure. 55% yield, Mn = 13 400, Mw/Mn = 1.81. 1H NMR (400 MHz, CDCl3): δ 7.88−7.69 (br, 2H), 3.04−2.73 (br, 4H), 2.00−1.71 (br, 4H), 1.44−1.15 (br, 24H), 0.97−0.78 (br, 6H). 13C{1H} NMR (100 MHz, CDCl3): δ 160.91, 157.14, 153.77, 129.47, 128.68, 125.44, 31.91, 30.70, 29.60, 29.56, 29.52, 29.45, 29.32, 22.69, 14.12. A part of the CHCl3-insoluble fraction of P1 was dissolved in 1,1,2,2-tetrachloroethane-d2 at 100 °C and evaluated by 1H NMR spectroscopy and MALDI-TOF-MASS. 1H NMR (600 MHz, C2D2Cl4, 373 K): δ 7.88−7.69 (br, 2H), 3.04−2.73 (br, 4H), 2.00−1.71 (br, 4H), 1.44−1.15 (br, 24H), 0.97−0.78 (br, 6H). Poly[(4,4′-di(2-octyldodecyl)-2,2′-bithiazole-5,5′-diyl)-(2,1,3-benzothiadiazole-4,7-diyl)] (P1′). A mixture of Pd(OAc)2 (1.12 mg, 0.0050 mmol), pivalic acid (0.0084 mL, 0.074 mmol), K2CO3 (85.7 mg, 0.62 mmol), 4,7-dibromo-2,1,3-benzothiadiazole (72.9 mg, 0.25 mmol), and 4,4′-di(2-octyldodecyl)-2,2′-bithiazole (181 mg, 0.25 mmol) was stirred in anhydrous DMAc (2.5 mL) for 24 h at 100

°C under a nitrogen atmosphere. Black-green solid of P1′ was isolated by the above-mentioned method in 83% yield. Mn = 49 500, Mw/Mn = 2.23. 1H NMR (600 MHz, CDCl3): δ 7.83 (br, 2H), 2.89 (br, 4H), 2.20 (br, 2H), 1.34−1.04 (br, 32H), 0.92−0.78 (br, 6H). 13C{1H} NMR (150 MHz, CDCl3): δ 160.70, 156.52, 153.88, 129.78, 129.26, 125.69, 37.97, 34.90, 33.48, 33.45, 31.93, 30.03, 29.74, 29.70, 29.67, 29.39, 26.46, 26.44, 22.70, 14.13 (6 signals of the alkyl group were overlapped). Poly[(4,4′-dinonyl-2,2′-bithiazole-5,5′-diyl)-(2,1,3-benzoxadiazole-4,7-diyl)] (P2). A mixture of Pd(OAc)2 (0.90 mg, 0.0040 mmol), pivalic acid (0.0068 mL, 0.060 mmol), K2CO3 (69.1 mg, 0.50 mmol), 4,7-dibromo-2,1,3-benzoxadiazole (55.6 mg, 0.20 mmol), and 4,4′dinonyl-2,2′-bithiazole (84.2 mg, 0.20 mmol) was stirred in anhydrous DMAc (0.67 mL) for 3 h at 100 °C under a nitrogen atmosphere. Black-green solid of P2 was isolated by the above-mentioned method in 29% yield. Mn = 5000, Mw/Mn = 1.23. 1H NMR (400 MHz, CDCl3): δ 7.65−7.59 (br, 2H), 3.06−2.74 (br, 4H), 1.98−1.70 (br, 4H), 1.48−1.16 (br, 24H), 0.96−0.79 (br, 6H). 13C{1H} NMR (100 MHz, CDCl3): δ 160.88, 157.89, 148.97, 130.84, 127.55, 120.99, 32.03, 31.10, 29.68, 29.57, 29.46, 22.82, 14.26 (2 signals of the alkyl group were overlapped). 1H NMR of CHCl3-insoluble fraction (600 MHz, C2D2Cl4, 373 K): δ 7.69 (s, 2H), 3.05 (s, 4H), 1.96 (s, 4H), 1.44−1.27 (br, 24H), 0.94 (t, 6H). Poly[(4,4′-dinonyl-2,2′-bithiazole-5,5′-diyl)-(2,1,3-benzoselenadiazole-4,7-diyl)] (P3). A mixture of Pd(OAc)2 (1.12 mg, 0.0050 mmol), pivalic acid (0.0085 mL, 0.075 mmol), K2CO3 (86.4 mg, 0.63 mmol), 4,7-dibromo-2,1,3-benzoselenadiazole (85.2 mg, 0.25 mmol), and 4,4′-dinonyl-2,2′-bithiazole (105 mg, 0.25 mmol) was stirred in anhydrous DMAc (0.83 mL) for 24 h at 120 °C under a nitrogen atmosphere. Black-green solid of P3 was isolated by the abovementioned method in 84% yield. Mn = 20 600, Mw/Mn = 2.35. 1H NMR (400 MHz, CDCl3): δ 7.79−7.59 (br, 2H), 3.06−2.67 (br, 4H), 2.02−1.71 (br, 4H), 1.49−1.11 (br, 24H), 0.95−0.78 (br, 6H). 13 C{1H} NMR (150 MHz, CDCl3): δ 161.00, 159.00, 157.09, 129.63, 129.03, 127.05, 31.90, 30.72, 29.63, 29.55, 29.50, 29.45, 29.31, 22.67, 14.11. Poly[(4,4′-dinonyl-2,2′-bithiazole-5,5′-diyl)-(2-(2-ethylhexyl)-2Hbenzotriazole-4,7-diyl)] (P4). A mixture of Pd(OAc)2 (1.08 mg, 0.0048 mmol), pivalic acid (0.0081 mL, 0.072 mmol), K2CO3 (82.9 mg, 0.60 mmol), 4,7-dibromo-2-(2-ethylhexyl)-2H-benzotriazole (93.4 mg, 0.24 mmol), and 4,4′-dinonyl-2,2′-bithiazole (101 mg, 0.24 mmol) was stirred in anhydrous DMAc (0.80 mL) for 6 h at 100 °C under a nitrogen atmosphere. Red solid of P4 was isolated by the abovementioned method in 88% yield. Mn = 16 300, Mw/Mn = 2.74. 1H NMR (400 MHz, CDCl3): δ 7.71−7.43 (br, 2H), 4.96−4.52 (br, 2H), 3.24−2.73 (br, 2H), 2.41−2.24 (br, 1H), 2.04−1.69 (br, 4H), 1.49− 1.15 (br, 32H), 1.06−0.77 (br, 12H). 13C{1H} NMR (150 MHz, CDCl3): δ 160.44, 156.37, 143.28, 129.11, 126.65, 122.42, 60.26, 40.46, 31.92, 30.76, 30.56, 29.65, 29.60, 29.58, 29.53, 29.35, 28.45, 23.96, 23.02, 22.69, 14.11, 10.54 (1 signal of the alkyl group was overlapped). Poly[(4,4′-dinonyl-2,2′-bithiazole-5,5′-diyl)-(2,3-dimethylquinoxaline-5,8-diyl)] (P5). A mixture of Pd(OAc)2 (1.12 mg, 0.0050 mmol), pivalic acid (0.0085 mL, 0.075 mmol), K2CO3 (86.4 mg, 0.63 mmol), 5,8-dibromo-2,3-dimethylquinoxaline (79.0 mg, 0.25 mmol), and 4,4′-dinonyl-2,2′-bithiazole (105 mg, 0.25 mmol) was stirred in anhydrous DMAc (0.83 mL) for 3 h at 100 °C under a nitrogen atmosphere. P5 was isolated by the above-mentioned method in 82% yield. Mn = 9600, Mw/Mn = 1.96. 1H NMR (400 MHz, CDCl3): δ 7.96−7.74 (br, 2H), 2.90−2.67 (br, 10H), 1.95−1.65 (br, 4H), 1.44− 1.00 (br, 24H), 0.95−0.75 (br, 6H). 13C{1H} NMR (100 MHz, CDCl3): δ 161.00, 156.36, 153.45, 139.35, 131.05, 129.88, 129.20, 31.83, 30.47, 29.57, 29.49, 29.38, 29.23, 23.06, 22.59, 14.03 (1 signal of the alkyl group was overlapped). 7383

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ASSOCIATED CONTENT

S Supporting Information *

Experimental details, characterization data, mass spectra of the compounds, DSC, and TGA curves. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail [email protected] (J.K.). *E-mail [email protected] (T.K.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank the Chemical Analysis Center of University of Tsukuba for the measurements of NMR spectra and MALDI-TOF-MS. The authors thank Dr. Takeshi Yasuda for the measurements of PYS and Mr. Ken Yoshimura and Mr. Takafumi Araki for the measurement of high-temperature GPC. This work was supported by Industrial Technology Research Grant Program in 2011 from New Energy and Industrial Technology Development Organization (NEDO) of Japan and partly supported by Grant-in-Aid for Grant-in-Aid for Young Scientists (B) (25810070), Challenging Exploratory Research (25620094), and Scientific Research (B) (25288052). J.K. acknowledges the JGC-S Scholarship Foundation for financial support.

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