Conjugated Copolymers of Poly(arylenevinylene)s: Synthesis by Ring

Jul 2, 2019 - A series of copolymers of poly(arylenevinylene)s have been prepared by ring-opening metathesis polymerization (ROMP) of cyclic conjugate...
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Conjugated Copolymers of Poly(arylenevinylene)s: Synthesis by Ring-Opening Metathesis Polymerization, Film Morphology, and Resonant Luminescence from Microspheres Yen-Jen Lin,† Hsin-Yu Chiang,† Osamu Oki,‡ Soh Kushida,‡ Shu-Wei Chang,† Shih-Ting Chiu,† Yohei Yamamoto,*,‡ Takuya Hosokai,§ and Masaki Horie*,† †

Department of Chemical Engineering, National Tsing Hua University, 101, Sec. 2, Kuang-Fu Road, Hsinchu 30013, Taiwan Department of Materials Science and Tsukuba Research Center for Energy Materials Science (TREMS), Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573, Japan § National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan

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‡

S Supporting Information *

ABSTRACT: A series of copolymers of poly(arylenevinylene)s have been prepared by ring-opening metathesis polymerization (ROMP) of cyclic conjugated monomers composed of cyclopentadithiophene, bis(thienyl)benzothiadiazole, or bithiophene using a second-generation Grubbs catalyst and the sequential monomer addition technique. The spectroscopic, electrochemical, and morphological properties of these polymers are tailored by changing the chemical structures and fractions of the monomers. The polymers self-assemble to form microspheres (diameter: 2−5 μm), which act as whispering-gallery-mode optical resonators. KEYWORDS: conjugated copolymers, ring-opening metathesis polymerization, film morphology, microspheres, resonant luminescence

1. INTRODUCTION Conjugated polymers have been widely investigated for their applications in optoelectronic devices1−3 such as organic photovoltaics,4−8 organic field-effect transistors,9−12 organic light-emitting diodes,13−15 sensors,16−19 and organic bioelectronics.20−22 Furthermore, conjugated polymers have been used to prepare microspheres that act as both fluorophore and resonator, displaying whispering-gallery-mode (WGM) photoluminescence (PL) and lasing.23−27 The use of conjugated polymers toward WGM lasers is advantageous for tuning the PL color from blue to red.26,27 Toward such organic optoelectronic applications, typical polymers are composed of alternating structures, most of which have been synthesized by step-growth polymerization such as Suzuki or Stille couplings or more recently by direct arylation polymerizations.28−35 Block copolymers comprising conjugated units have attracted significant interest as they possess multiple photoactive and electronically active functions.36−38 In addition, they exhibit a specific morphology such as microphase separation.37,38 Generally, such synthesis can be achieved by chaingrowth polymerization, end-functional polymer copolymerization, or end-functional polymer coupling.36,39−41 Ring-opening metathesis polymerization (ROMP)42,43 allows the production of well-defined conjugated poly(arylenevinylene)s with low © XXXX American Chemical Society

molecular weight distributions and few structural defects through a ruthenium carbene-catalyzed reaction using a Grubbs initiator.37,44−51 Yu and Turner et al. reported the synthesis of homopolymers and block copolymers of poly(phenylenevinylene)s with precise molecular weight by ROMP of cyclophanedienes.37,44,48−50 Despite the good controllability of polymerization by ROMP, the monomers are limited to relatively simple structures such as phenylenevinylenes,37,44−51 thienylenevinylenes,52 and naphthylenevinylenes53 because of a multiple-step synthesis with low overall yield. Recently, we have reported the synthesis of a donor− acceptor conjugated copolymer of poly(arylenevinylene)s comprising electron-donating cyclopentadithiophene (CPDT) and accepting bis(thienyl)benzothiadiazole (DTBT) by ROMP of ring-strained cyclophanetrienes.54 In addition, the self-assembly and surface morphology of the CPDT monomers and homopolymers were studied.55 It is essential to conduct comprehensive studies on the synthesis of conjugated copolymers using new combinations of cyclic conjugated monomers, tailoring their spectroscopic properties and solidstate morphologies. Here, we report the synthesis of Received: June 13, 2019 Accepted: July 2, 2019 Published: July 2, 2019 A

DOI: 10.1021/acsapm.9b00549 ACS Appl. Polym. Mater. XXXX, XXX, XXX−XXX

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ACS Applied Polymer Materials

Figure 1. (a) Structures of cyclic conjugated monomers. (b) Synthetic scheme of conjugated copolymers by ROMP by using Grubbs II catalyst and the sequential monomer addition technique. (c) Structures of copolymers.

Table 1. Polymerization Results polymer P1 P2 P3 P4 P5a P5b P5c P6a P6b P6c P6d

M1a CPDT-t DTBT-t BT-d DTBT-t BT-d BT-d BT-d DTBT-t DTBT-t DTBT-t DTBT-t

M2b

Mnc

Mw/Mnc e

CPDT-t CPDT-t CPDT-t CPDT-t BT-d BT-d BT-d BT-d

e

19100 18600e 10500 35600e 14200 13600 6400 10700 10200 7700 11400

1.94 1.74e 2.40 2.10e 1.80 1.77 1.60 2.40 3.24 1.76 2.49

n/md

weight fraction of M1

45/0 34/0 29/0 34/39 25/12 19/15 14/3 10/15 10/13 9/7 8/20

1.00 1.00 1.00 0.53 0.64 0.51 0.80 0.50 0.55 0.66 0.37

a First monomer. bSecond monomer. cMn and Mw/Mn are determined by GPC (THF eluent and polystyrene standards). dDegree of polymerization n/m was calculated from the 1H NMR spectrum and Mn. eData from our previous report.54

conjugated copolymers of poly(arylenevinylene)s comprising CPDT, DTBT, and bithiophene (BT). The copolymers are expected to have different crystallinity and aggregating properties, as tailored by the combination of monomers, their chemical structures, and their molecular weights. Therefore, the film morphology of the copolymers is studied by atomic force microscopy (AFM). Finally, the polymers are used to prepare microspheres to find appropriate combinations of the conjugated units for efficient WGM PL. This is the first observation of WGM PL from conjugated copolymer micro-

resonators synthesized by ROMP with the sequential monomer addition technique.

2. RESULTS AND DISCUSSION Figure 1a shows the chemical structures of cyclic conjugated monomers. CPDT-t and DTBT-t comprising trimers of CPDT and DTBT, respectively, were obtained by using a previously reported method.54 The dimer and trimer of BT-containing monomers, BT-d and BT-t, respectively, were synthesized by McMurry coupling of 3,3′-dihexyl-2,2′-bithiophene-5,5′-dicarbaldehyde using TiCl4/Zn in THF (Table S1). The obtained B

DOI: 10.1021/acsapm.9b00549 ACS Appl. Polym. Mater. XXXX, XXX, XXX−XXX

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ACS Applied Polymer Materials monomers were characterized by 1H NMR, 13C NMR, and fast atom bombardment (FAB) mass spectroscopies (Figures S1− S8). As shown in Figures 1b and 1c, P1, P2, and P3 were synthesized by ROMP of the cyclic conjugated monomers using a second-generation Grubbs catalyst at 120 °C in pxylene solution. The polymerization was quenched by the addition of excess ethyl vinyl ether. BT-d and BT-t showed similar reactivities in ROMP (Table S2). Therefore, we selected BT-d for the following polymerizations because of its higher yield and easier purification compared with BT-t in the monomer synthesis. The number-average molecular weight (Mn) and the molecular weight distribution (Mw/Mn) of the polymers were measured by gel permeation chromatography (GPC) eluted with THF and using polystyrene standards; these results are summarized in Table 1. P4 was synthesized by ROMP of DTBT-t as the first monomer, followed by addition of CPDT-t as the second monomer.54 Similarly, in the synthesis of the P5 series, monomer BT-d was first polymerized before the second monomer CPDT-t was added to the reaction mixture, changing the monomer feed ratios and giving P5a−P5c. The 1 H NMR spectrum of P5a shows peaks at 2.49 and 1.84 ppm, which were assigned to the aliphatic methylene protons on the side chains of the BT unit and CPDT unit, respectively (Figure 2). In contrast, the 1H NMR spectrum of a statistic copolymer

P4, P5b, and P6a are purple, green, and orange, respectively (Figure 3a). They exhibit absorption spectra across a wide range because of the presence of two units (Figures 3b and 3c). The statistic copolymer obtained from BT-d and CPDT-t shows absorption peaks in the shorter wavelength region (529 nm) than P5b (Figure S21). All spectra and data are summarized in Figure S22 and Table S3, respectively. In addition, the electrochemical properties of the polymers were investigated by cyclic voltammetry (Figure S23). To verify the electronic state, the molecular orbitals were calculated using density functional theory (DFT) for the simulated molecular models of the predicted oligomers produced by ROMP (Figures S25 and S26). To investigate the effects of the compositions of the polymers, a morphology study was conducted by noncontact-mode AFM. The phase and topography images of the polymers are summarized in Figure 4 and Figure S28, respectively. P1 showed a smooth and amorphous morphology (Figure 4a). By contrast, P2 showed aggregation of the polymer, possibly because of its lower solubility as compared with the other polymers (Figure 4b). P3 exhibited spherical vesicles, with roughness intermediate between P1 and P2 (Figure 4c), suggesting a reasonable level of aggregation property. Thus, morphology tuning can be conducted using combinations of these units with different levels of amorphous/aggregative property. In the copolymer P4, aggregation of the DTBT−vinylene unit was mitigated because of the presence of the amorphous CPDT−vinylene unit (Figure 4d). P6a formed a smoother surface than P4, giving an amorphous-like morphology (Figure 4e). On the contrary, P5b provided long-range cracks (length: 100−500 nm; Figure 4f). This result encouraged us to conduct further morphology studies for other compositions. Thus, P5c with an increased composition of aggregative BT−vinylene units was investigated, in expectation of an interesting morphology. In fact, P5c exhibited periodic wave-like shapes (length: ∼120 nm; width: ∼10 nm; Figures 4g and 4h). For further understanding of the structural development of the copolymer, we investigated the film of P5c by grazing incident small- and wide-angle scattering (GISAXS and GIWAXS). The GISAXS data for the thin film of P5c (Figure S29) show enhanced intensity in the q-region near 0.01 Å−1 (d = ca. 10 nm), revealing formation of additionally large rod-like domains (model-fitted in the inset of Figure S29). However, no lamellar ordering peak could be observed in the GISAXS profile, as that shown in the AFM image in Figures 4g and 4h, presumably due to a locally limited lamellar ordering of the rod-like micelles. Furthermore, the 2D GIWAXS pattern reveals no crystal reflections of the polymers from the rodlike micelles. In contrast, GISAXS data (Figure S30) for P1 film shows much lower intensity in the similar q-region near 0.01 Å−1, suggesting much less phase separation for similar rod-like micelles; no crystalline peaks could be observed in the GIWAXS pattern of the film (Figure S30). To verify the effect of the copolymer synthesized by the sequential monomer addition technique on morphology, a control experiment was conducted using a mixture of P1 and P3 (Figure 4i). The mixture showed a coexistent morphology composed of an amorphous region derived from P1 and aggregations from P3. Self-assembly of the block copolymers in solution was conducted by using a vapor diffusion method (Figure 5a).56,57 P2 formed well-defined microspheres (Figure 5c), and P1

Figure 2. 1H NMR spectra of (a) P1, (b) P3, and (c) P5a in a CDCl3 solution.

obtained from BT-d and CPDT-t shows multiple peaks in the aliphatic region (Figure S14). From the integration ratio of these peaks and Mn, the repeating unit of P5a was calculated to be n/m = 25/12 (a weight fraction of M1 = 0.64). P6a−P6d were also synthesized by ROMP of DTBT-t, followed by ROMP of BT-d, changing the monomer feed ratios. These copolymers were also calculated by a similar manner; these results are summarized in Table 1. However, a relatively high molecular weight distribution around 2 might suggest potential occurrence of secondary metathesis. As shown in Figure 3a, the polymers exhibit quite different colors in chloroform solution: P1, P2, and P3 are blue, red, and yellow, respectively. P3 shows absorption peaks in the shorter wavelength region (432 nm), whereas P1 and P2 show peaks in the longer and middle wavelength regions (608 and 665 nm for P1 and 376 and 493 nm for P2; Figures 3b and 3c). These UV−vis absorption properties are attributed to the different backbone structures and conjugated systems. The copolymers show intermediate colors between two polymers: C

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Figure 3. (a) Photo of the polymers in chloroform solutions. UV−vis absorption spectra of (b) P1, P3, and P5b and (c) P2, P3, and P6a.

give ill-defined aggregates. P2, P4, and P6 contain DTBT, which has a benzothiadiazole group attached with two bulky alkylated thiophenes on 4,7-positions of the benzothiadiazole. Such bulky substituents significantly twist polymer backbone structure to give spherical morphology. Among them, BT seems to have favorable effect on the microsphere formation than CPDT due to less planarity with 3,3′-alkyl substituents on bithiophenes. Therefore, the combination of DTBT and BT in P6 series tends to form the spherical morphology, while the combination of DTBT and CPDT in P4 hardly form microspheres. Micrometer-sized fluorescent spheres often act as optical resonators, in which the generated PL is confined inside the microspheres via total internal reflection at the polymer/air interface. As a result of the self-interference of the confined photon, the PL spectrum displays sharp and periodic PL lines; this is termed WGM PL (Figure 6a). For the well-defined microspheres formed from P2, P6b, and P6c (Figures 5c, 5f, and 5g, respectively), clear WGM PL peaks appear when the

yielded only ill-defined aggregates (Figure 5b). Of the copolymers, P4 hardly formed any microspheres, indicating that the CPDT unit hampered the formation of microspheres (Figure 5d). On the contrary, the P6 series formed microspheres whose surface morphologies were highly dependent on the ratio of the compositions. P6a−P6c, comprising similar or higher DTBT fractions than BT, provided welldefined microspheres with a smooth surface morphology (Figures 5e−5g); on the contrary, P6d, with a higher BT fraction, hardly formed any microspheres (Figure 5h). Consequently, a reasonable DTBT fraction is required for microsphere formation. We now consider the effect of the molecular structure of the polymers on the formation of the microspheres. It was reported that a highly twisted polymer backbone was essential for the formation of spherical morphology.58 P1, P4, and P5 contain the planar CPDT fused ring, which stretches the polymer backbone structures. As a result of the planar structure, these polymers hardly form microspheres but only D

DOI: 10.1021/acsapm.9b00549 ACS Appl. Polym. Mater. XXXX, XXX, XXX−XXX

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Figure 4. AFM phase images of polymers (a) P1, (b) P2, (c) P3, (d) P4, (e) P6a, (f) P5b, and (g) P5c with a range of 1 × 1 μm2, (h) P5c with a range of 0.5 × 0.5 μm2, and (i) a mixture of P1 and P3 with a molar ratio of P1:P3 = 20:80. The rectangles below the images represent the approximate Mn of each unit.

diameter is >2.8 μm (Figures 6b, 6d, and 6e, respectively). For the smaller microspheres, the large curvature causes leakage loss, which reduces the efficiency of the light confinement and leads to suppression of the WGM PL.27 On the contrary, microspheres of P6a hardly show any WGM PL, even in the case where the diameter reaches 3.0 μm (Figure 6c). This is possibly due to the rather rough surface morphology, which scatters the confined photon in the microsphere (Figure 5e). Microspheres of P6d did not show WGM PL because the surface of the microspheres is quite rough (Figure 6f).

was essential, and the sphere formation was tailored by the ratio of DTBT−vinylene/BT−vinylene, based on their compatibility. These microspheres exhibited efficient WGM PL depending on the smooth surface morphology of the microspheres. Controlling film surface morphology and microsphere formation remains challenging. Our demonstration of the synthesis of such copolymers via a facile polymerization method will be useful for first screenings of polymers toward potential applications in organic optoelectronics. The conjugated copolymers are potentially useful as light-sensing and harvesting materials in photosensor and photoelectric conversion devices, based on their tunable photoabsorption and emission wavelengths. In addition, since the microspheres act as optical resonators, they can be applied to microlasers, miniaturized optical circuit elements, and miniaturized chemical and biosensing tools.

3. CONCLUSION A series of all-conjugated copolymers of poly(arylenevinylene)s have been synthesized by ROMP of cyclic conjugated monomers with the sequential monomer addition technique, providing diversity of chemical structures. These copolymers showed the superimposed properties derived from two units, i.e., the intermediate colors of two units and wide-range UV− vis absorption spectra, as compared with the polymers synthesized from a single monomer. In AFM observations, the polymer films exhibited quite different morphologies. Consequently, the combination of amorphous CPDT−vinylene with a higher proportion of crystalline BT−vinylene provided specific periodic wave-like shapes. On the contrary, for microsphere preparation, the presence of DTBT−vinylene

4. EXPERIMENTAL SECTION 4.1. Synthesis of BT-d and BT-t. TiCl4 (1.61 mL, 30.0 equiv) was added to a suspension of zinc (0.750 g, 22.5 equiv) in THF (26 mL, 0.02 M) at 0 °C under a nitrogen atmosphere, and then the suspension was heated to 55 °C. After the temperature of the suspension reached to 55 °C, a solution of 3,3′-dihexyl-[2,2′bithiophene]-5,5′-dicarbaldehyde (200 mg, 0.514 mmol, 1.00 equiv) and pyridine (0.6 mL) in THF (7 mL) was added by an autoinjector E

DOI: 10.1021/acsapm.9b00549 ACS Appl. Polym. Mater. XXXX, XXX, XXX−XXX

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Figure 5. (a) Schematic of the preparation of the microspheres by the vapor diffusion method. SEM images of the self-assembled precipitates of (b) P1, (c) P2, (d) P4, (e) P6a, (f) P6b, (g) P6c, and (h) P6d. with flow rate of 0.3 mL/min for 60 min. The reaction mixture was cooled to room temperature and then was concentrated by a rotary evaporator to remove THF. The purification was performed by filtration through a flash column of silica gel (hexane:dichloromethane = 1:1) and further purification by SEC (flow rate = 14 mL min−1) using chloroform as the eluent. The first fraction of SEC gave BT-d (30 mg, 16% yield). 1H NMR (500 MHz, CDCl3): δ 6.87 (s, 6H, 3thiophene), 6.53 (s, 6H, −CC), 2.39 (t, J = 8.0 Hz, 12H, CH2), 1.68 (m, 12H, CH2), 1.54 (m, 12H, CH2), 1.23 (m, 12H, CH2), 1.18 (m, 12H, CH2), 0.83 (m, 18H, CH3). 13C NMR (125 MHz, CDCl3): δ 141.7, 138.4 (Cquart), 130.9, 129.9 (3-thiophene), 123.2 (−CC), 31.6, 30.7, 29.7, 29.1, 28.7 (CH2), 22.6, 14.1 (CH3). FABMS calcd for [C66H91S6]+ (m/z): 1076, found: 1076. The second fraction of SEC afforded BT-t (41 mg, 22% yield). 1H NMR (500 MHz, CDCl3): δ 6.63 (s, 4H, 3-thiophene), 6.62 (s, 4H, −CC), 2.53 (t, J = 7.5 Hz, 8H, CH2), 1.54 (m, 16H, CH2), 1.25 (m, 16H, CH2), 0.83 (m, 12H, CH3). 13C NMR (125 MHz, CDCl3): δ 141.4, 133.4 (Cquart), 128.9 (3-thiophene), 125.6 (−CC), 31.7, 30.9, 29.7, 29.1 (CH2), 22.6, 14.1 (CH3). FABMS calcd for [C44H61S4]+ (m/z): 717, found: 717. 4.2. Synthesis of Homopolymers P3. Second-generation Grubbs catalyst (2.05 mg, 6.67 mol %) was dissolved in anhydrous p-xylene (725 μL, 0.05 M) in a 10 mL Schlenk tube under a nitrogen atmosphere. This solution was added to BT-d (26 mg, 0.036 mmol, 1.0 equiv) in a 5 mL Schlenk tube. After the reaction mixture was stirred at 120 °C for 6 min, ethyl vinyl ether (1.0 mL) was added to quench the reaction and stirred at room temperature for 10 min. The resulting mixture was then poured into MeOH (70 mL) to precipitate. The precipitate was washed with MeOH and acetone and then dried under vacuum to give P3 as the yellow powder (18 mg, 68% yield). 1H NMR (500 MHz, CDCl3): δ 6.92 (s, 2H, 3thiophene), 6.89 (s, 2H, vinyl), 2.49 (m, 4H, CH2), 1.24 (m, 16H, CH2), 0.85 (m, 6H, CH3). GPC (polystyrene standards in THF): Mn = 10460, PDI = 2.4 (ideal Mn = 10760).

4.3. Synthesis of P5 Series. A second-generation Grubbs catalyst (1.37 mg, 14.3 mol %) was dissolved in anhydrous p-xylene (226 μL, 0.05 M) in a 10 mL Schlenk tube under a nitrogen atmosphere. This solution was added to BT-d (8.1 mg, 0.0113 mmol, 1.0 equiv) in a 5 mL Schlenk tube, and the reaction mixture was stirred at 120 °C for 6 min. Then, CPDT-t (14.2 mg, 0.0113 mmol) was added into the reaction mixture, and the reaction mixture was stirred at 120 °C for 6 min. After the resulting mixture was cooled to room temperature, ethyl vinyl ether was added and stirred at room temperature for 10 min to quench the mixture. The mixture was then poured into MeOH (70 mL). The precipitate was washed with MeOH and acetone and then dried under vacuum to obtain P5a as a dark green powder (12 mg, 55%). 1H NMR (500 MHz, CDCl3): δ 6.92 (m, 4H, 3-thiophene and vinyl of CPDT), 6.89 (m, 4H, vinyl of BT and 3-CPDT), 2.49 (br, 4H, CH2 of BT), 1.84−1.8 (br s, 4H, CH2 of CPDT), 1.245 (m, 16H, CH2 of the BT), 1.02−0.92 (m, 18H, CH2 of the CPDT), 0.85 (m, 6H, CH3 of the BT), 0.75 (br s, 6H, CH3 of the CPDT), 0.62 (br s, 6H, CH3 of the CPDT). GPC (polystyrene standards in THF): Mn = 14200, PDI = 1.8 (ideal Mn = 14000). P5b was synthesized by a similar procedure using secondgeneration Grubbs catalyst (1.37 mg, 14.3 mol %), anhydrous pxylene (332 μL, 0.05 M), BT-d (11.9 mg, 0.0165 mmol, 1.0 equiv), CPDT-t (21.2 mg, 0.0165 mmol). GPC: Mn = 13600, PDI = 1.77 (ideal Mn = 14000). P5c was synthesized by a similar procedure using secondgeneration Grubbs catalyst (1.13 mg, 16.7 mol %), anhydrous pxylene (399 μL, 0.05 M), BT-d (14.3 mg, 0.0199 mmol, 1.0 equiv), CPDT-t (5.1 mg, 0.0040 mmol, 0.2 equiv). GPC: Mn = 6400, PDI = 1.60 (ideal Mn = 29960). 4.4. Synthesis of P6 Series. A second-generation Grubbs catalyst (1.06 mg, 16.7 mol %) was dissolved in anhydrous p-xylene (150 μL, 0.05 M) in a 10 mL Schlenk tube under a nitrogen atmosphere. This solution was added to DTBT-t (12.4 mg, 0.0075 mmol, 1.0 equiv) in a 5 mL Schlenk tube, and the reaction mixture was stirred at 120 °C for 6 min. Then, BT-d (8.1 mg, 0.0113 mmol) was added into the F

DOI: 10.1021/acsapm.9b00549 ACS Appl. Polym. Mater. XXXX, XXX, XXX−XXX

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Figure 6. (a) Principles of PL confinement and interference to show WGM luminescence. PL spectra of single microspheres of (b) P2, (c) P6a, (d) P6b, (e) P6c, and (f) P6d with various diameters. reaction mixture, and the reaction mixture was stirred at 120 °C for 6 min. After the resulting mixture was cooled to room temperature, ethyl vinyl ether was added and stirred at room temperature for 10 min to quench the mixture. The mixture was then poured into MeOH (70 mL). The precipitate was washed with MeOH and acetone and then dried under vacuum to obtain P6a as dark green (14 mg, 70%). 1 H NMR (500 MHz, CDCl3): δ 7.67 (s, 2H, BT), 7.09 (s, 2H, 3thiophene of DTBT), 7.00 (s, 2H, vinyl of DTBT), 6.916 (s, 2H, 3thiophene of BT), 6.89 (s, 2H, vinyl of BT), 2.60 (br s, 4H, CH2 of DTBT), 2.49 (br s, 4H, CH2 of the H3), 1.23−1.01 (m, 18H, CH2 of the DTBT), 0.85 (m, 6H, CH3 of the BT), 0.75 (br s, 6H, CH3 of the DTBT), 0.66 (br s, 6H, CH3 of the DTBT). GPC (polystyrene standards in THF): Mn = 10700, PDI = 2.4 (ideal Mn = 16340). P6b was synthesized by a similar procedure using secondgeneration Grubbs catalyst (1.89 mg, 20.0 mol %), anhydrous pxylene (222 μL, 0.05 M), DTBT-t (12.2 mg, 0.0111 mmol, 1.0 equiv), BT-t (11.9 mg, 0.0111 mmol, 1.0 equiv). GPC: Mn = 10200, PDI = 3.24 (ideal Mn = 10865). P6c was synthesized by a similar procedure using secondgeneration Grubbs catalyst (1.72 mg, 20.0 mol %), anhydrous pxylene (202 μL, 0.05 M), DTBT-t (11.1 mg, 0.0101 mmol, 1.0 equiv), BT-t (5.4 mg, 0.0050 mmol, 0.5 equiv). GPC: Mn = 7700, PDI = 1.76 (ideal Mn = 8178). P6d was synthesized by a similar procedure using secondgeneration Grubbs catalyst (1.58 mg, 20.0 mol %), anhydrous pxylene (186 μL, 0.05 M), DTBT-t (10.2 mg, 0.0093 mmol, 1.0 equiv), BT-t (20.0 mg, 0.0186 mmol, 2.0 equiv). GPC: Mn = 11400, PDI = 2.49 (ideal Mn = 16240). 4.5. DFT Calculations. DFT calculations for oligomers were conducted using the Gaussian 09W package software [functional/ basis set: B3LYP/6-31G(d)] and a supercomputer in Research Center for Computational Science, Okazaki, Japan. For the calculations of electronic states and geometrical optimization of molecules shown in

Figure S25, the alkyl side chains of all the molecules were replaced by ethyl groups to reduce computational costs without influencing the energy of HOMO and LUMO, both of which are located only at the conjugated rings or conjugated main chains. For the optimization of CPDT-BT and BT-DTBT, the optimized geometry of the monomer without the side chains was first prepared and employed by constructing that oligometric initial geometry with ethyl groups.

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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsapm.9b00549.

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Synthesis, material characterization data, GPC elution curves, additional optical and electrochemical properties, and AFM images (PDF)

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Soh Kushida: 0000-0002-4474-9529 Yohei Yamamoto: 0000-0002-2166-3730 Masaki Horie: 0000-0002-7734-5694 Funding

This work was financially supported by the Ministry of Science and Technology Taiwan, National Tsing Hua University (107Q2708E1) and a Grant-in-Aid for Scientific Research G

DOI: 10.1021/acsapm.9b00549 ACS Appl. Polym. Mater. XXXX, XXX, XXX−XXX

Article

ACS Applied Polymer Materials

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(JP17H05142, JP16H02081, and JP15KK0182) from the Japan Society for the Promotion of Science (JSPS). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful to Prof. K. U-Ser Jeng, Dr. Wei-Ru Wu, and Dr. Chun-Jen Su of Taiwan National Synchrotron Radiation Research Center for GISAXS/WAXS measurements and enlightening discussion. The computations were performed using Research Center for Computational Science, Okazaki, Japan.

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DOI: 10.1021/acsapm.9b00549 ACS Appl. Polym. Mater. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acsapm.9b00549 ACS Appl. Polym. Mater. XXXX, XXX, XXX−XXX