Alkoxy-Substituted Anthra[1,2-

Alkoxy-Substituted Anthra[1,2-...
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Article Cite This: Macromolecules XXXX, XXX, XXX−XXX

Alkoxy-Substituted Anthra[1,2‑c:5,6‑c′]bis([1,2,5]thiadiazole) (ATz): A New Electron-Acceptor Unit in the Semiconducting Polymers for Organic Electronics Hiroki Mori,† Shuhei Nishinaga,‡ Ryosuke Takahashi,‡ and Yasushi Nishihara*,† †

Research Institute for Interdisciplinary Science and ‡Division of Earth, Life, and Molecular Sciences, Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushimanaka, Kita-ku, Okayama 700-8530, Japan

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ABSTRACT: A new type of thiadiazole-based acceptor unit and its donor−acceptor copolymers were synthesized and characterized to develop the high-performance semiconducting polymers for organic field-effect transistors (OFETs) and organic photovoltaics (OPVs). We successfully synthesized an anthra[1,2-c:5,6-c′]bis([1,2,5]thiadiazole) (ATz) core and ATz-quaterthiophene copolymers. These copolymers possess a wide energy gap of ca. 1.8 eV and a deeper HOMO energy levels around −5.4 eV than that of typical thiadiazole−oligothiophene copolymers. Such weak electron-accepting nature may be due to the decreased electron affinity of the ATz core by an existence of alkoxy groups with strong electron-donating ability. The ATz copolymers exhibited good semiconducting properties with hole mobility of up to 0.03 cm2 V−1 s−1 and photovoltaic response with PCE of up to 5.7%, despite the unfavorable molecular orders, thin-film structure, and/or amorphous structure.

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OFET11,24 and fullerene-free solar cells,25−29 a new class of electron-accepting unit is highly desired. Among the acceptor units reported, an array of thiadiazolecontaining π-electron cores such as benzothiadiazole (BTz), 18,20,23,30−36 thiadiazolopyridine (PT), 37−40 and naphthobisthiadiazole (NTz)17,41−43 has been utilized for high-performance D−A polymers (Figure 1). BTz is one of the most useful and representative acceptor unit with simplest chemical structure in thiadiazole-based acceptor. In D−A polymers the BTz unit has an electron-deficient 1,2,5thiadiazole ring and strong o-benzoquinoidal nature, leading to large electron affinity (i.e., low-lying LUMO energy level) and narrow energy gap (Eg).6,44,45 In addition, the BTz core can facilitate hydrogen bonds between nitrogen atoms in the 1,2,5-thiadiazole ring and hydrogen atoms of neighboring aryl groups, which can enhance its coplanarity, resulting in wellordered packing structure.6,18,20,34 Indeed, several BTz-based D−A polymers have narrow bandgap (1.5−1.6 eV) and longrange ordered structure even in blended film, and their OFET and OPVs exhibited excellent field-effect mobility over 1 cm2 V−1 s−1 46 and power conversion efficiency (PCE) over 10%.20,34,47,48 In addition to such excellent features, the HOMO and LUMO energy levels of BTz-based D−A polymers can easily be tuned because 5,6-positions of BTz can be functionalized with various electron-donating and -withdrawing groups. For instance, the installation of alkoxy

INTRODUCTION Semiconducting polymer-based organic electronics involving organic field-effect transistors (OFETs) and organic photovoltaics (OPVs) are one of the promising candidates for nextgeneration wearable electronics because of their potential features such as light weight, low-cost production, and stretchable devices.1−5 Among a large number of p-type semiconducting polymers developed, donor−acceptor (D−A)type polymers that combine electron-rich aromatic cores with electron-deficient aromatic cores are believed to develop highperformance materials for OFETs and OPVs, owing to their broad absorption around visible region, deep highest occupied molecular orbital (HOMO) energy level, and high charge carrier mobility.6−11 Since their electronic and thin-film structures strongly depend on their donor and acceptor units, the optimal choice of donor and acceptor units can tune the light-harvesting ability and HOMO−lowest unoccupied molecular orbital (LUMO) energy levels.6−8,11−13 Moreover, the length, symmetry, and planarity of both donor and acceptor units significantly affect the backbone arrangement, attachment density of side chains, and side-chain placement of the D−A polymers, which often influence the π−π stacking motif and molecular ordering and thus charge carrier mobility.9,13−23 Therefore, the optimization of donor and acceptor units is highly important for high-performance electronic device. However, the development of the highperformance acceptor units has been limited compared to donor units. In terms of developing not only p-type D−A polymers but also n-type semiconductors for n-channel © XXXX American Chemical Society

Received: June 11, 2018

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DOI: 10.1021/acs.macromol.8b01230 Macromolecules XXXX, XXX, XXX−XXX

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Figure 1. Structures of thiadiazole-based acceptor units and target ATz copolymers.

In this study, we designed and synthesized anthra[1,2-c:5,6c′]bis([1,2,5]thiadiazole) (ATz, Figure 1) as a readily functionalized thiadiazole-containing acceptor unit to develop the high-performance D−A polymers. ATz has two thiadiazole rings fused onto an anthracene core, which is expected to be a large electron affinity similar to BTz. In fact, it has lower LUMO and almost the same HOMO energy levels compared to BTz and its derivatives, as is evident from DFT calculations (Figure S1a−f). Since ATz has more rigid and extended πelectron core and higher symmetry (C2h) than that of various BTz derivatives (C2v), the incorporation of an ATz core into the polymer backbone can further enhance the effective πorbital overlaps between neighboring polymer main chains and thereby may provide the densely π-stacking structure with long-range orders.57,58 As an additional feature of ATz, it can easily tune the HOMO−LUMO energy levels because selective functionalization at 6,12-positions of ATz can be feasible. Herein, we report the synthesis of an ATz framework and ATz-based D−A polymers PATz4T to develop a new class of p-type semiconductor. To evaluate the potential of the ATz core for high-performance electronics, a simple quaterthiophene was chosen as the donor unit in the D−A polymers. Alkoxy groups were installed into 6,12-positions of ATz to ensure enough solubility of polymers because the ATz core has stronger intermolecular interactions originated in its extended π-electron core and an increased symmetry. In addition, alkoxy-substituted ATz can easily be synthesized by using commercially available starting materials. The alkoxy-substituted ATz have almost the same HOMO and LUMO energy levels in spite of strong electron-donating alkoxy groups. In this study, linear long (dodecyloxy) and short (hexyloxy) alkoxy side chains were chosen to control the packing structure because we reasoned that more sterically bulky branched alkoxy groups at 6,12-positions of ATz may prevent the effective π-orbital overlaps. Furthermore, we explored physicochemical properties as well as typical transistor and solar cell characteristics of PATz4T.

groups into 5,6-positions of a BTz core can furnish a high coplanarity via intramolecular noncovalent interaction and high solubility.49 In addition, two alkoxy groups can reduce an electron affinity of a BTz core, leading to narrow absorption with a wide bandgap in D−A polymers.50 Hence, dialkoxyBTz-based polymers showed an excellent OPV performance in both polymer/C6050 and non-fullerene solar cells51 as widebandgap p-type semiconductors. The electron-accepting nature of a BTz core can be further increased by the introduction of cyano or fluoride groups. The former gave significantly lower LUMO energy levels than that of BTz-based polymers, which can act as an n-type semiconductor in OFETs.52 The latter can decrease HOMO and LUMO energy levels, maintaining the almost same energy gap. Moreover, the fluorinated BTz formed a well-ordered structure in the solid state by an increased intra- or intermolecular interaction of fluorine atoms, leading to an enhanced hole transporting ability and thus excellent OFET46 and OPV20,34,47,48 performances. In other thiadiazole-based acceptors, PT is also a well-known acceptor unit for high-performance organic electronics.37−40 Compared with a BTz counterpart, PT-based polymers have smaller energy gaps and reduced HOMO and LUMO energy levels due to the more electron-deficient fused pyridine ring. In particular, the PT-based polymers showed the record hole mobility of 23.7 cm2 V−1 s−1 in polymer transistors owing to macroscopic aligned structure.53 NTz is a representative πextended thiadiazole-based acceptor unit with much larger electron affinity than that of a BTz counterpart because of the existence of doubly fused thiadiazole rings. The incorporation of NTz into a polymer backbone can lead to a deeper HOMO energy level and a smaller energy gap.17 Moreover, its πextended core with a high symmetry can enhance an intermolecular interaction and thereby promote the selfassembling nature. In particular, NTz-based polymers formed a highly ordered thin-film structure, leading to an efficient hole transport under a thick film over 300 nm, resulting in high PCE over 10%.43,54−56 However, the two thiadiazole-based acceptors cannot easily be modified to control the electronic state and polymer main chain of the D−A polymers. Thus, the development of a new class of thiadiazole-based acceptor unit that can easily be functionalized is highly important for highperformance electronics.

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EXPERIMENTAL SECTION

General. All the reactions were carried out under an Ar atmosphere using standard Schlenk techniques. Glassware was dried in an oven (130 °C) and heated under reduced pressure prior to use.

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DOI: 10.1021/acs.macromol.8b01230 Macromolecules XXXX, XXX, XXX−XXX

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Hz, 4H), 7.96 (d, J = 9.6 Hz, 2H), 8.55 (d, J = 9.6 Hz, 2H). 13C{1H} NMR (151 MHz, CDCl3, rt): δ 14.29, 22.87, 25.91, 30.34, 31.98, 75.81, 120.85, 120.91, 127.40, 128.39, 150.35, 151.63, 155.75. Anal. Calcd for C26H30N4O2S2: C, 63.13; H, 6.11, N, 11.33%. Found: C, 63.01; H, 6.00, N, 11.22%. A Representative Synthetic Procedure for 6a−6b. 4,10-Bis(4-(2hexyldecyl)thiophene-2-yl)-6,12-bis(dodecyloxy)anthra[1,2-c:5,6c′]bis([1,2,5]thiadiazole) (6a). In a 100 mL two-necked roundbottomed flask, bromine (1.0 mL, 19 mmol) was added to a mixture of 3a (630 mg, 0.95 mmol) and iron chloride(III) (78 mg, 0.48 mmol) in acetic acid (60 mL). After the reaction mixture was stirred at 100 °C for 48 h, the mixture was cooled to room temperature and poured into water (100 mL). The obtained solid was collected by filtration and washed with methanol. After the removal of the solvent under reduced pressure, the crude mixture was used for a next step without further purification. To a deaerated solution of the crude mixture containing 4a (710 mg) and 4-(2-hexyldecyl)-2-trimethylstannylthiophene (5a) (1.0 g, 2.2 mmol) in anhydrous toluene (45 mL) in a 100 mL two-necked round-bottomed flask was added tetrakis(triphenylphosphine)palladium(0) (40 mg, 0.034 mmol). The reaction mixture was heated to a gentle reflux for 24 h. The mixture was cooled to room temperature and added 1 M potassium fluoride aqueous solution (20 mL). The crude mixture was extracted with dichloromethane (30 mL × 3) and washed with brine and dried over MgSO4. After the removal of the solvent under reduced pressure, the obtained solid was purified by silica gel column chromatography with hexane−dichloromethane (5:2) as the eluents (Rf = 0.39) to afford 6a (546 mg, 0.53 mmol) in 45% yield (two steps from 3a) as an orange solid; mp 78−79 °C. FT-IR (KBr, cm−1): 2920 (s), 2850 (s), 2300 (w), 1587 (s), 1465 (s), 1377 (s), 1312 (s), 1263 (s), 1043 (m), 855 (m). 1H NMR (600 MHz, CDCl3, rt): δ 0.88 (m, 18H), 1.20−1.55 (m, 84H), 1.81 (m, 2H), 2.23 (m, 4H), 2.68 (d, J = 7.2 Hz, 4H), 4.28 (t, J = 7.2 Hz, 4H), 7.05 (s, 2H), 8.15 (s, 2H), 8.80 (s, 2H). 13C{1H} NMR (151 MHz, CDCl3, rt): 14.30, 14.33, 22.88, 22.91, 26.76, 26.86, 29.57, 29.61, 29.88, 29.92, 29.95, 29.98, 30.02, 30.28, 30.62, 32.12, 32.14, 32.15, 33.57, 33.59, 35.34, 39.13, 75.85, 119.90, 122.60, 122.83, 126.53, 128.34, 130.55, 139.18, 143.36, 150.26, 152.31, 153.79. Anal. Calcd for C78H122N4O2S4: C, 73.41; H, 9.64, N, 4.39%. Found: C, 73.16; H, 9.83, N, 4.34%. 4,10-Bis(4-(2-octyldodecyl)thiophene-2-yl)-6,12-bis(hexyloxy)anthra[1,2-c:5,6-c′]bis([1,2,5]thiadiazole) (6b). Orange solid. Yield: 69% (two steps from 3b) (hexane:dichloromethane = 5:2 as the eluents, Rf = 0.42); mp 86−87 °C. FT-IR (KBr, cm−1): 2922 (s), 2851 (s), 2340 (m), 1586 (s), 1458 (s), 1377 (s), 1311 (s), 1263 (s), 1058 (m), 864 (m). 1H NMR (600 MHz, CDCl3, rt): δ 0.85 (t, J = 7.2 Hz, 12H), 1.00 (t, J = 7.2 Hz, 6H), 1.23−1.55 (m, 72H), 1.85 (m, 6H), 2.23 (m, 4H), 2.68 (d, J = 6.6 Hz, 4H), 4.28 (t, J = 6.6 Hz, 4H), 7.06 (s, 2H), 8.14 (s, 2H), 8.78 (s, 2H). 13C{1H} NMR (151 MHz, CDCl3, rt): δ 14.27, 14.35, 22.84, 22.97, 26.40, 26.82, 29.52, 29.84, 30.24, 30.52, 32.08, 32.17, 33.53, 35.33, 39.08, 75.77, 119.84, 122.59, 125.74, 126.47, 128.28, 130.45, 139.14, 143.30, 150.19, 152.25, 153.73. Anal. Calcd for C74H114N4O2S4: C, 72.85; H, 9.42, N, 4.59%. Found: C, 73.02; H, 9.62, N, 4.56%. A Representative Synthetic Procedure for 7a−7b. 4,10-Bis(5bromo-4-(2-hexyldecyl)thiophene-2-yl)-6,12-bis(dodecyloxy)anthra[1,2-c:5,6-c′]bis([1,2,5]thiadiazole) (7a). To the solution of 6a (128 mg, 0.10 mmol) in THF (10 mL) in a 20 mL Schlenk tube was slowly added N-bromosuccinimide (NBS) (35.6 mg, 0.22 mmol). The reaction mixture was stirred for 6 h in the dark. Then water was added, and the organic phase was extracted with dichloromethane (15 mL × 3). The combined organic layers were washed with brine and dried over MgSO4. After the removal of the solvent under reduced pressure, the obtained solid was purified by a short column chromatography with silica gel using dichloromethane as the eluent. Then, the crude product was recrystallized by ethyl acetate to give 7a (138 mg, 0.096 mmol) in 96% yield as an orange solid; mp 88−89 °C. FT-IR (KBr, cm−1): 2922 (s), 2853 (s), 2372 (m), 1586 (w), 1516 (w), 1463 (m), 1430 (s), 1377 (s), 1313 (s), 1261 (s), 1045 (m), 851 (m), 721 (s). 1H NMR (600 MHz, CDCl3, rt): δ 0.87 (m, 18H), 1.20−1.56 (m, 84H), 1.81 (m, 2H), 2.22 (m, 4H), 2.60 (d, J = 6.6 Hz,

Dehydrated tetrahydrofuran (THF), N,N-dimethylformamide (DMF), and toluene were purchased from Kanto Chemicals Co., Ltd. For thin layer chromatography (TLC) analyses throughout this work, Merck precoated TLC plates (silica gel 60 GF254, 0.25 mm) were used. Silica gel column chromatography was carried out using Silica gel 60 N (spherical, neutral, 40−100 μm) from Kanto Chemicals Co., Ltd. The 1H and 13C{1H} NMR spectra were recorded on a Varian INOVA-600 (600 MHz) spectrometer. NOESY spectra were obtained in deuterated chloroform with a Varian 400MR spectrometer. Infrared spectra were recorded on a Shimadzu IRPrestige-21 spectrophotometer. Elemental analyses were carried out with a PerkinElmer 2400 CHN elemental analyzer at Okayama University. Polymerizations were performed with a Biotage initiator microwave reactor. Molecular weights of polymers were determined by gel-permeation chromatography (GPC) with a TOSOH HLC8321GPC/HT and TSKgel GMHHR-H HT using a polystyrene standard and o-dichlorobenzene (o-DCB) as the eluent at 140 °C. 1,2,5,6-Tetraaminoanthraquinone (1), 59 4-(2-hexyldecyl)-2trimethylstannylthiophene (5a),60 4-(2-octyldodecyl)-2-trimethylstannylthiophene (5b),60 and 5,5′-bis(trimethylstannyl)-2,2′-bithiophene (8)61 were synthesized according to the reported procedures. All other chemicals were used without further purification unless otherwise indicated. Anthra[1,2-c:5,6-c′]bis([1,2,5]thiadiazole)-6,12-diol (2). To a solution of 1,2,5,6-tetraaminoanthroquinone (1, 4.1 g, 15.3 mmol) and triethylamine (13.0 mL, 91.8 mmol) in THF (80 mL) in a 200 mL three-necked round-bottomed flask was slowly added thionyl chloride (8.9 mL, 122 mmol) at 0 °C. The reaction mixture was warmed to room temperature and stirred for 12 h. The resulting mixture was poured into crashed ice, and precipitated solid was collected by filtration and washed with chloroform, DMSO, and acetone. The obtained solid was purified by thermal gradient vacuum sublimation (source temperature: 270 °C under ∼10−1 Pa) to afford the compound 2 (1.6 g, 4.9 mmol) in 32% yield as a dark red solid; mp >270 °C. FT-IR (KBr, cm−1): 3251 (br), 2340 (m), 1667 (s), 1524 (s), 1425 (s), 1352 (s), 1276 (s), 1001 (s), 817 (m), 610 (s). 1H NMR (600 MHz, CDCl3, rt): δ 7.87 (d, J = 9.6 Hz, 2H), 8.66 (d, J = 9.6 Hz, 2H), 10.87 (s, 2H). 13C{1H} NMR (151 MHz, CDCl3, rt) was not obtained due to its low solubility. Anal. Calcd for C14H6N4O2S2: C, 51.53; H, 1.85; N, 17.17%. Found: C, 51.46; H, 1.79, N, 17.07%. A Representative Synthetic Procedure for 3a−3b. Synthesis of 6,12-Bis(dodecyloxy)anthra[1,2-c:5,6-c′]bis([1,2,5]thiadiazole) (3a). In a 100 mL two-necked round-bottomed flask, KOH (272 mg, 4.8 mmol) was added to a stirred suspension of anthra[1,2-c:5,6c′]bis([1,2,5]thiadiazole)-6,12-diol (2, 395 mg, 1.2 mmol) in DMF (40 mL). After the solution mixture was stirred for 10 min, 1bromododecane (1.2 mL, 4.8 mmol) was added. The reaction mixture was stirred at 100 °C for 48 h. Then, the mixture was cooled to room temperature and extracted with chloroform (50 mL × 3). The combined organic layers were washed with brine and dried over MgSO4. After the removal of the solvent under reduced pressure, the obtained solid was purified by a short column chromatography with silica gel using dichloromethane as the eluent. Then, the crude product was recrystallized by ethyl acetate to give the compound 3a (634 mg, 0.96 mmol) in 79% yield as an orange solid; mp 120−121 °C. FT-IR (KBr, cm−1): 2920 (s), 2850 (s), 2342 (m), 1463 (s), 1427 (s), 1305 (s), 1248 (s), 1030 (s), 820 (m). 1H NMR (600 MHz, CDCl3, rt): δ 0.88 (t, J = 6.6 Hz, 6H), 1.28−1.55 (m, 32H), 1.67 (m, 4H), 2.21 (m, 4H), 4.22 (t, J = 6.6 Hz, 4H), 7.96 (d, J = 9.6 Hz, 2H), 8.54 (d, J = 10.2 Hz, 2H). 13C{1H} NMR (151 MHz, CDCl3, rt): δ 14.28, 22.85, 26.24, 29.52, 29.79, 29.81, 29.84, 29.86, 29.87, 30.34, 32.08, 75.80, 120.84, 120.89, 127.40, 128.39, 150.34, 151.63, 155.73. Anal. Calcd for C38H54N4O2S2: C, 68.84; H, 8.21, N, 8.45%. Found: C, 68.77; H, 8.22, N, 8.40%. 6,12-Bis(hexyloxy)anthra[1,2-c:5,6-c′]bis([1,2,5]thiadiazole) (3b). Orange solid. Yield: 69%; mp 135−136 °C. FT-IR (KBr, cm−1): 2927 (s), 2868 (s), 2347 (m), 1456 (s), 1427 (s), 1306 (s), 1248 (s), 1028 (s), 820 (m). 1H NMR (600 MHz, CDCl3, rt): δ 0.96 (t, J = 6.6 Hz, 6H), 1.43−1.50 (m, 8H), 1.67 (m, 4H), 2.21 (m, 4H), 4.22 (t, J = 6.6 C

DOI: 10.1021/acs.macromol.8b01230 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules 4H), 4.21 (t, J = 6.6 Hz, 4H), 7.94 (s, 2H), 8.57 (s, 2H). 13C{1H} NMR (151 MHz, CDCl3, rt): δ 14.26, 14.30, 22.84, 22.89, 26.73, 26.89, 29.55, 29.59, 29.84, 29.91, 29.92, 29.97, 30.01, 30.04, 30.09, 30.25, 30.60, 32.10, 32.11, 32.13, 33.57, 33.60, 34.54, 38.76, 75.73, 112.07, 119.74, 122.25, 125.49, 128.19, 129.76, 138.76, 142.53, 150.13, 152.02, 153.24. Anal. Calcd for C78H120Br2N4O2S4: C, 65.34; H, 8.44; N, 3.91%. Found: C, 65.43; H, 8.67; N, 3.86%. 4,10-Bis(5-bromo-4-(2-octyldodecyl)thiophene-2-yl)-6,12-bis(hexyloxy)anthra[1,2-c:5,6-c′]bis([1,2,5]thiadiazole) (7b). Orange solid. Yield: 91%; mp 89−90 °C. FT-IR (KBr, cm−1): 2922 (s), 2851 (s), 2343 (m), 1585 (w), 1506 (w), 1458 (m), 1427 (s), 1377 (s), 1314 (s), 1263 (s), 1051 (m), 854 (m), 723 (s). 1H NMR (600 MHz, CDCl3, rt): δ 0.85 (t, J = 7.2 Hz, 12H), 1.01 (t, J = 7.2 Hz, 6H), 1.23−1.55 (m, 72H), 1.82 (m, 6H), 2.19 (m, 4H), 2.60 (d, J = 7.2 Hz, 4H), 4.21 (t, J = 6.4 Hz, 4H), 7.94 (s, 2H), 8.58 (s, 2H). 13C{1H} NMR (151 MHz, CDCl3, rt): δ 14.26, 14.40, 22.84, 23.04, 26.53, 26.75, 29.52, 29.55, 29.84, 29.88, 30.25, 30.57, 32.08, 32.09, 32.22, 33.57, 34.59, 38.77, 75.73, 112.09, 119.74, 122.24, 125.50, 128.19, 129.72, 138.76, 142.54, 150.13, 152.02, 153.24. Anal. Calcd for C74H112N4O2S4Br2: C, 64.51; H, 8.19, N, 4.07%. Found: C, 64.60; H, 8.24, N, 4.00%. A Representative Synthetic Procedure for PATz4T-oR1R2. Synthesis of Polymers PATz4T-o12HD. Monomers 7a (71.7 mg, 0.05 mmol) and 8 (24.6 mg, 0.05 mmol), tetrakis(triphenylphosphine)palladium(0) (1.2 mg, 2 μmol), and toluene (2.5 mL) were added to a reaction vessel, which was sealed and refilled with argon. The reaction mixture was heated at 180 °C for 40 min in a microwave reactor. After being cooled to room temperature, the reaction mixture was poured into 100 mL of methanol containing 5 mL of concentrated hydrochloric acid and stirred for 3 h. The precipitate was then subjected to sequential Soxhlet extraction with methanol, hexane, and chloroform to remove low-molecular-weight fractions. The residue was extracted with chlorobenzene, and concentrated solution was poured into 50 mL of methanol. The formed precipitates were collected by filtration and dried in vacuo to afford the target polymer PATz4T-o12HD (69.1 mg, 96%) as a metallic purple solid. GPC (o-DCB, 140 °C): Mn = 63.3 kDa, Mw = 124.6 kDa, PDI = 1.97. 1 H NMR (600 MHz, toluene-d8, 80 °C): δ 0.88−1.04 (br, 18H), 1.25−1.85 (br, 88H), 2.32−2.41 (br, 4H), 3.07−3.18 (br, 4H), 4.20− 4.30 (br, 4H), 7.18−7.25 (br, 4H), 7.29−7.38 (br, 2H), 8.39−8.52 (br, 2H). Anal. Calcd for C86H126N4O2S6: C, 71.72; H, 8.82; N, 3.89%. Found: C, 71.66; H, 8.59; N, 3.74%. Polymer PATz4T-o6OD. Monomers 7b (68.9 mg, 0.05 mmol) and 8 (24.6 mg, 0.05 mmol), tetrakis(triphenylphosphine)palladium(0) (1.2 mg, 2 μmol), and toluene (2.5 mL) were subjected to the polymerization procedure, and sequential Soxhlet extraction with the same solvents used for PATz4T-o12HD was employed to obtain PATz4T-o6OD (61.7 mg, 89%) as a metallic purple solid. GPC (oDCB, 140 °C): Mn = 41.5 kDa, Mw = 68.3 kDa, PDI = 1.64. 1H NMR (600 MHz, toluene-d8, 80 °C): δ 0.85−1.01 (br, 18H), 1.17−1.85 (br, 80H), 2.29−2.40 (br, 4H), 3.10−3.21 (br, 4H), 4.20−4.33 (br, 4H), 7.21−7.25 (br, 4H), 7.32−7.37 (br, 2H), 8.45−8.49 (br, 2H). Anal. Calcd for C82H118N4O2S6: C, 71.15; H, 8.59; N, 4.05%. Found: C, 71.02; H, 8.38; N, 3.95%. Instrumentation. UV−vis absorption spectra were measured using a Shimadzu UV-2450 UV−vis spectrometer. Cyclic voltammograms (CVs) were recorded on electrochemical analyzer CHI-600B in acetonitrile containing tetrabutylammonium hexafluorophosphate (TBAPF6, 0.1 M) as supporting electrolyte at a scan rate of 100 mV/s. A Pt electrode (surface area: A = 0.071 cm2, BAS), an Ag/Ag+ (Ag wire in 0.01 M AgNO3/0.1 M TBAPF6/CH2Cl2 or CH3CN), and a Pt wire electrode were used as working, reference, and counter electrodes, respectively. Samples of the polymer films were prepared by drop-casting on a working electrode from their chloroform solutions. All the potentials were calibrated with the standard ferrocene/ferrocenium redox couple (Fc/Fc+: E1/2 = +0.44 V for CH2Cl2, and E1/2 = +0.04 V for CH3CN measured under identical conditions). Dynamic force-mode atomic force microscopy was carried out using an SPA 400-DFM (SII Nano Technologies). Grazing incidence wide-angle X-ray diffraction (GIWAXS) analyses

were carried out at SPring-8 on beamline BL46XU. The samples were irradiated at a fixed angle on the order of 0.12° through a Huber diffractometer with an X-ray energy of 12.39 keV (λ = 1 Å), and the GIWAXS patterns were recorded on a 2D image detector (Pilatus 300K). Films of the polymers and blended films with PC61BM were fabricated by spin-coating on the ZnO-treated ITO or FOTS-treated n+-Si/SiO2 substrate. Geometry optimizations and normal-mode calculations were performed at the B3LYP/6-31G(d) level using the Gaussian 09, Revision D. 01, program package.62 Fabrication of Inverted Bulk-Heterojunction Solar Cells. The inverted bulk-heterojunction solar cells were fabricated as follows. ZnO precursor solution was prepared by hydrolysis of Zn(OAc)2.63 The ITO substrates (ITO, Geomatec Co. Ltd., thickness = 150 nm, sheet resistance 10% in Polymer Solar Cells. J. Mater. Chem. A 2017, 5, 17619−17631. (48) Liu, Y.; Zhao, J.; Li, Z.; Mu, C.; Ma, W.; Hu, H.; Jiang, K.; Lin, H.; Ade, H.; Yan, H. Aggregation and Morphology Control Enables Multiple Cases of High-Efficiency Polymer Solar Cells. Nat. Commun. 2014, 5, 5293. (49) Kini, G. P.; Oh, S.; Abbas, Z.; Rasool, S.; Jahandar, M.; Song, C. E.; Lee, S. K.; Shin, W. S.; So, W.-W.; Lee, J.-C. Effects on Photovoltaic Performance of Dialkyloxy-benzothiadiazole Copolymers by Varying the Thienoacene Donor. ACS Appl. Mater. Interfaces 2017, 9, 12617−12628. (50) Ko, S.-J.; Hoang, Q. V.; Song, C. E.; Uddin, M. A.; Lim, E.; Park, S. Y.; Lee, B. H.; Song, S.; Moon, S.-J.; Hwang, S.; Morin, P.-O.; Leclerc, M.; Su, G. M.; Chabinyc, M. L.; Woo, H. Y.; Shin, W. S.; Kim, J. Y. High-Efficiency Photovoltaic Cells with Wide Optical Band gap Polymers Based on Fluorinated Phenylene-Alkoxybenzothiadiazole. Energy Environ. Sci. 2017, 10, 1443−1455. (51) Lin, Y.; Zhao, F.; Wu, Y.; Chen, K.; Xia, Y.; Li, G.; Prasad, S. K. K.; Zhu, J.; Huo, L.; Bin, H.; Zhang, Z.-G.; Guo, X.; Zhang, M.; Sun, Y.; Gao, F.; Wei, Z.; Ma, W.; Wang, C.; Hodgkiss, J.; Bo, Z.; Inganäs, O.; Li, Y.; Zhan, X. Mapping Polymer Donors toward High-Efficiency Fullerene Free Organic Solar Cells. Adv. Mater. 2017, 29, 1604155. (52) Casey, A.; Han, Y.; Fei, Z.; White, A. J. P.; Anthopoulos, T. D.; Heeney, M. Cyano Substituted Benzothiadiazole: A Novel Acceptor Inducing n-Type Behaviour in Conjugated Polymers. J. Mater. Chem. C 2015, 3, 265−275. (53) Tseng, H.-R.; Phan, H.; Luo, C.; Wang, M.; Perez, L. A.; Patel, S. N.; Ying, L.; Kramer, E. J.; Nguyen, T.-Q.; Bazan, G. C.; Heeger, A. K

DOI: 10.1021/acs.macromol.8b01230 Macromolecules XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.macromol.8b01230 Macromolecules XXXX, XXX, XXX−XXX