Tuning the Semiconducting Behaviors of New Alternating

Mar 31, 2015 - The results reveal that semiconducting properties of DPPA1, DPPA2, and DPPA3 can be tuned by varying the linkage positions of azulene w...
2 downloads 6 Views 3MB Size
Download PDF
Article pubs.acs.org/Macromolecules

Tuning the Semiconducting Behaviors of New Alternating Dithienyldiketopyrrolopyrrole−Azulene Conjugated Polymers by Varying the Linking Positions of Azulene Jingjing Yao, Zhengxu Cai, Zitong Liu,* Chenmin Yu, Hewei Luo, Yang Yang, Sifen Yang, Guanxin Zhang, and Deqing Zhang* Beijing National Laboratory for Molecular Sciences, Organic Solids Laboratory, Institute of Chemistry, Chinese Academy of Sciences Beijing 100190, P. R. China S Supporting Information *

ABSTRACT: Three new conjugated polymers DPPA1, DPPA2, and DPPA3 with dithienyldiketopyrrolopyrrole (DPP) and azulene moieties were synthesized and characterized. The five-membered rings of azulene are connected with DPP in DPPA1 and DPPA2, whereas the seven-membered ring of azulene is incorporated into the backbone of DPPA3. The LUMO energy of DPPA3, which was determined on the basis of the respective cyclic voltammograms and absorption spectra, is lower than those of DPPA1 and DPPA2. OFETs were successfully fabricated with thin films of DPPA1, DPPA2, and DPPA3. Thin films of DPPA1 and DPPA2 exhibit p-type semiconducting properties with hole mobilities up to 0.97 cm2 V−1 s−1, whereas typical ambipolar behavior is found for thin film of DPPA3 with hole and electron mobilities reaching 0.062 cm2 V−1 s−1 and 0.021 cm2 V−1 s−1, respectively. The results reveal that semiconducting properties of DPPA1, DPPA2, and DPPA3 can be tuned by varying the linkage positions of azulene with DPP moieties. Furthermore, DPPA1, DPPA2, and DPPA3 were tested preliminarily as photovoltaic materials. The power conversion efficiency (PCE) reaches 2.04% for the blending thin film DPPA1 with PC71BM.

■

donors in these semiconducting D−A polymers.5,6,12 In comparison, conjugated D−A polymers with aromatic hydrocarbons as electron donors were less intensively studied.13 In this paper, we report three conjugated D−A polymers DPPA1, DPPA2, and DPPA3 entailing DPP and azulene moieties (Scheme 1). The selection of azulene is based on the following considerations: (i) azulene is a resonance-stabilized nonalternant aromatic hydrocarbon with an electrically positive seven-membered ring and an electrically negative fivemembered ring, leading to a dipole moment of 1.08 D;14 (ii) azulene possesses a small HOMO−LUMO gap. In fact, conjugated molecules containing azulene C1, C2, and C3 (Scheme 1) were described previously.15 2,2′-Bithiophene and thieno[3,2-b]thiophene in C1 and C2, respectively, were linked with the electron-rich five-membered ring of azulene, whereas three azulenes were head-to-tail connected in C3. Thin films of C1 and C2 were found to behave as p-type semiconductors with hole mobility of ca. 10−2 cm2 V−1 s−1, but thin film of C3 exhibited n-type semiconducting property with electron mobility of 0.29 cm2 V−1 s−1. A number of polymers entailing azulene moieties such as P1−P40 in Scheme 1 were

INTRODUCTION In recent years, alternating conjugated electron donor (D)− acceptor (A) polymers have received increasing attention because they behave as solution-processable semiconductors, which promise for applications in low-cost, large-area, and flexible electronic devices, such as field effect transistors (FETs), photovoltaics (PVs), and light-emitting diodes (LEDs).1−3 Various electron donors and acceptors were selected to construct conjugated D−A polymers for developing semiconducting materials of high performance.4 Among them, dithienyldiketopyrrolopyrrole (DPP) has been intensively investigated as electron accepting moiety to build conjugated D−A polymers.5 For instance, Liu, Ong, and co-workers reported the DPP−thieno[3,2-b]thiophene conjugated polymer exhibiting p-type semiconducting property with hole mobility up to 10.5 cm2 V−1 s−1.6 Meanwhile, DPP−selenophene alternating conjugated polymers were found to behave as ambipolar semiconductors with hole and electron mobilities reaching 8.84 cm2 V−1 s−1 and 4.34 cm2 V−1 s−1, respectively.7 Apart from DPP, other electron-accepting moieties including naphthalenediimide,8 isoindigo,9 benzothiadiazole,10 and Pechmann dye11 were also linked to various electron donors to yield the respective semiconducting D−A polymers. Heterocycles and fused heterocycles such as thiophene and thieno[3,2-b]thiophene were widely employed as electron © XXXX American Chemical Society

Received: January 24, 2015 Revised: March 17, 2015

A

DOI: 10.1021/acs.macromol.5b00158 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules

Scheme 1. Chemical Structures of DPPA1, DPPA2, and DPPA3 as Well as Those of Azulene-Containing Conjugated Small Molecules and Polymers

synthesized and investigated.16 Among them, conjugated polymers P1−P7 were found to show relatively high electrical conductivity upon p-doping or protonation.16a,b Electronic spectral variations were detected for conjugated polymers P8− P18 after protonation and oxidation, and they were successfully utilized for electrochromic devices.16c,d For conjugated copolymers P19−P28 which contain two azulene regioisomers in the backbones, their optoelectronic and stimuli-responsive properties can be systematically modulated by varying the ratios of the two regioisomers in the backbones.16e Although azulenesubstituted methacrylate polymers P29−P36 were proved useful as cathode modification layers in bulk-heterojunction solar cells,16f semiconducting properties of azulene-entailing conjugated polymers and their applications as active layers in FETs and photovoltaic cells were rarely reported, to the best of our knowledge. Imahori and co-workers have just recently reported P37−P40 for application in solar cells, but power conversion efficiencies were rather low.16g Herein we describe the synthesis and semiconducting behaviors of azulene-containing conjugated D−A polymers DPPA1, DPPA2, and DPPA3 with DPP moieties. The results reveal that DPPA1 and DPPA2 in which the five-membered rings of azulene moieties are incorporated in their conjugated backbones exhibit p-type semiconducting behaviors, whereas DPPA3 with the seven-membered ring of azulene moieties in the backbone behaves as ambipolar semiconductor. Thus, the semiconducting properties of these azulene-containing conjugated polymers can be tuned by varying the connection positions of azulene moieties in the conjugated backbones.

Moreover, DPPA1 is also tested as electron donor for organic photovoltaic cells.

■

RESULTS AND DISCUSSION Synthesis and Characterization. The synthesis of DPPA1, DPPA2, and DPPA3 is shown in Scheme 2. Compounds 1, 3, and 7 were synthesized according to the Scheme 2. Synthetic Routes of DPPA1, DPPA2, and DPPA3

B

DOI: 10.1021/acs.macromol.5b00158 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules

Table 1. Absorption, Onset Redox Potentials, HOMO/LUMO Energies, and Band Gaps of DPPA1, DPPA2, and DPPA3 λmaxa (nm) (εmax, M−1 cm−1)b polymer

solution

film

Ered1onset (eV)c

ELUMO (eV)d

Eox1onset (eV)c

EHOMO (eV)d

Egcv (eV)e

Egopt (eV)f

DPPA1 DPPA2 DPPA3

667 (71000) 670 (51000) 627 (25000)

686, 745 694 675

−1.25 −1.21 −1.16

−3.55 −3.59 −3.64

0.33 0.32 0.34

−5.13 −5.12 −5.14

1.58 1.53 1.50

1.33 1.38 1.23

Absorption maxima in CHCl3 solution (1.0 × 10−5 M for each polymer) and the spin-coated thin film. bMolar extinction coefficient (εmax, M−1 cm−1). cOnset potentials (V vs Fc/Fc+) for reduction (Eredlonset) and oxidation (Eoxlonset). dEstimated with the following equation: HOMO = −(Eox1onset + 4.8) eV and LUMO = −(Ered1onset + 4.8) eV. eBased on redox potentials. fBased on the absorption spectral data. a

respective reported procedures.16b,17 Compound 2 was obtained by bromination of 1 with NBS at −78 °C for 3.0 h in 15.5% yield. The low yield of 2 is owing to the formation of tribromo- and tetrabromo-substituted byproducts. This is probably caused by the fact that thiophene moieties in 1 become more active because of the strong electron donating feature of the five-membered ring of azulene. Such side reactions could not be avoided even at −78 °C. Borylation of 3 yielded 4 in 7.15% yield by using Pd(dppf)2Cl2·CH2Cl2 as the catalyst and KOAc as the base. Similarly, the electron donating five-membered ring of azulene makes the diboronic esters become more active, and thus coupling between 3 and 4 can occur, leading to azulene oligomers. Accordingly, the yield of 4 is low. The Suzuki cross-coupling of the respective dibromoazulene compounds 2 and 7 with 6 with Pd2(dba)3/ P(o-tol)3 as the catalyst yielded DPPA1 and DPPA3, respectively. Similarly, DPPA2 was prepared by the coupling between compounds 5 and 4. We also tried to prepare DPPA2 via the Suzuki coupling of 6 with 3, but it turned out that the degree of polymerization was very low. The three polymers DPPA1, DPPA2, and DPPA3 were precipitated out from the respective reaction mixtures after addition of methanol. They were purified by Soxhlet extraction with methanol, hexane, acetone, and chloroform, followed by precipitation in methanol again. DPPA1, DPPA2, and DPPA3 were obtained in 66.9%, 77.8%, and 61.6% yields, respectively. The chemical structures of three polymers were verified by 1H NMR, solid-state 13C NMR, and elemental analysis (see Experimental Section). DPPA1, DPPA2, and DPPA3 can be dissolved in CHCl3, 1,1,2,2-tetrachloroethane, toluene, and other aromatic solvents, and concentrations of these polymers can reach 20 mg/mL. Mw of DPPA1, DPPA2, and DPPA3 were determined to be 41.7, 38.1, and 49.4 kg mol−1 with PDI of 3.4, 2.7, and 3.3, respectively, by gel permeation chromatography (GPC). Based on the thermogravimetric analysis (TGA) data shown in Figure S1, the thermal decomposition (at 5% weight loss) temperatures of DPPA1, DPPA2, and DPPA3 were found to be higher than 300 °C. On the basis of differential scanning calorimetry (DSC) measurements, DPPA1 exhibited an exothermic peak around 261 °C, whereas weak endothermic signals around 250 and 232 °C were detected for DPPA2 and DPPA3, respectively. No phase transitions were observed below 200 °C. These DSC results may indicate that the polymer interchain packing within thin film of DPPA1 is different from those within thin films of DPPA2 and DPPA3. Optical and Electrochemical Properties. Cyclic voltammetric measurements were carried out for thin films of DPPA1, DPPA2, and DPPA3. As depicted in Figure S2, thin films of DPPA1 and DPPA2 show irreversible oxidation and reduction waves, whereas a quasi-reversible reduction wave and an irreversible oxidation wave are detected for thin film of DPPA3. The redox potential of ferrocene was measured under the same

condition (see Figure S2), and the respective onset oxidation and reduction potentials of these polymer thin films were presented by reference to the redox potential of ferrocene/ ferrocenium (Fc/Fc+) (see Table 1). According to previous reports,18 HOMO and LUMO energies of DPPA1, DPPA2, and DPPA3 as well as their bandgaps were estimated based on the following equations: LUMO = −(Ered1onset + 4.8) eV and HOMO = −(Eox1onset + 4.8) eV. As listed in Table 1, the HOMO/LUMO energies of DPPA1, DPPA2, and DPPA3 were estimated to be −5.13/−3.55, −5.12/−3.59, and −5.14/− 3.64 eV, respectively. It is obvious that DPPA3 exhibits lower LUMO energy in comparison with those of DPPA1 and DPPA2. This can be interpreted by considering the fact that the electron withdrawing seven-membered ring of azulene is incorporated in the backbone of DPPA3, whereas the electron donating five-membered ring of azulene is connected in the backbones of DPPA1 and DPPA2. It may be anticipated that DPPA1 and DPPA2 behave as p-type semiconductors, whereas DPPA3 is potentially to be ambipolar semiconductor. Figure 1 shows the absorption spectra of the solutions and thin films of DPPA1, DPPA2, and DPPA3. Solutions of

Figure 1. Normalized UV−vis absorption spectra of DPPA1, DPPA2, and DPPA3 in CHCl3 (1.0 × 10−5 M) and their thin films.

DPPA1, DPPA2, and DPPA3 exhibit strong absorptions at 667 nm (εmax = 71 000 M−1 cm−1), 670 nm (εmax = 51 000 M−1 cm−1), and 627 nm (εmax = 25 000 M−1 cm−1), respectively. In comparison, absorptions of thin films of DPPA1, DPPA2, and DPPA3 are red-shifted; their maxima absorptions are redshifted by 19, 24, and 48 nm compared to the respective maxima absorptions of their solutions. These spectral shifts may be owing to the π−π interactions between the conjugated polymer chains according to previous studies.19 On the basis of the respective onset absorptions of their thin films, their optical gaps were estimated to be 1.33, 1.38, and 1.23 eV, respectively. DFT Calculations. To provide more insights into the structural and electronic features of DPPA1, DPPA2, and C

DOI: 10.1021/acs.macromol.5b00158 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules

be beneficial for hole and electron charge transporting, respectively.15b Thin-Film FETs. Bottom-gate/bottom-contact field-effect transistors (FETs) with thin films of DPPA1, DPPA2, and DPPA3 were fabricated with conventional techniques (see Experimental Section).The performances of FETs were measured under a nitrogen atmosphere. Figure 3 shows the transfer and output characteristics of FETs with thin films of three polymers after thermal annealing. The results reveal that thin films of DPPA1 and DPPA2 exhibit p-type semiconducting behaviors under a nitrogen atmosphere, whereas thin film of DPPA3 shows typical ambipolar semiconducting property. The p-type semiconducting property of DPPA1 and DPPA2 is related to their relatively high HOMO energies, whereas the ambipolar semiconducting behavior of DPPA3 can be attributed to the relatively low LUMO energy (see Table 1). Thus, the semiconducting behaviors of these DPP-azulene conjugated polymers can be tuned by varying the linkage positions of azulene in their backbones; the connection of DPP with the five-membered ring of azulene leads to p-type semiconductors whereas the incorporation of the sevenmembered ring into the conjugated backbone yields the ambipolar semiconducting property. Table 2 summarizes the performance data of FETs based on thin films of DPPA1, DPPA2, and DPPA3 before and after thermal annealing at different temperatures. Charge mobilities of thin films of DPPA1, DPPA2, and DPPA3 increased after thermal annealing at appropriate temperatures. For instance, hole mobility of the as-prepared FET with thin film of DPPA1 was measured to be 0.12 cm2 V−1 s−1, and it increased to 0.97 cm2 V−1 s−1 after annealing under vacuum at 120 °C for 1 h. But, it decreased to 0.36 cm2 V−1 s−1 after annealing at 160 °C under the same condition. A similar trend holds true for thin film of DPPA2 (see Table 2): μh reached 0.08 cm2 V−1 s−1 after thermal annealing at 80 °C for 1.0 h.20 For DPPA3, the μh and μe of the as-prepared thin film FET were measured to be 0.01 cm2 V−1 s−1 and 2.4 × 10−3 cm2 V−1 s−1, respectively. Both μh and μe increased to 0.062 cm2 V−1 s−1 and 0.021 cm2 V−1 s−1, respectively, after annealing at 120 °C for 1.0 h. But, both hole

DPPA3, density functional theory (DFT) calculations at the B3LYP/6-31G(d,p) level were performed for their respective repeat units. HOMO/LUMO energies of DPPA1, DPPA2, and DPPA3 were calculated to be −4.70/−2.56 eV, −4.68/−2.44 eV, and −4.83/−2.60 eV, respectively. Although discrepancies exist between the calculated HOMO/LUMO energies and those determined based on the respective cyclic voltammetric data, the calculations also indicate that DPPA3 possesses lower HOMO and LUMO energies. As depicted in Figure 2, HOMO

Figure 2. Calculated molecular orbitals and HOMO/LUMO energies of each repeated unit of DPPA1 (a), DPPA2 (b), and DPPA3 (c) at the B3LYP/6-31G(d,p) level. The alkyl chains are replaced with methyl groups for computational simplicity.

orbitals of the repeated units of DPPA1, DPPA2, and DPPA3 are well distributed over their conjugated backbones. But, the LUMO orbital of DPPA1 is mainly resided on the DPP moiety, and that of DPPA2 is mostly distributed on the DPP moiety and the seven-membered ring of azulene makes slight contribution. However, the LUMO orbital of DPPA3 is well distributed over the whole backbone. This may explain the observation that thin films of DPPA1 and DPPA2 show p-type semiconducting behaviors whereas thin film of DPPA3 behaves as an ambipolar semiconductor (see below). This is because the good distribution of HOMO and LUMO orbitals is expected to

Figure 3. Transfer and output characteristics for FETs with DPPA1 (a, b), DPPA2 (c, d), and DPPA3 (e, f, g, h) after annealing at 120, 80, and 120 °C, respectively. D

DOI: 10.1021/acs.macromol.5b00158 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules

Table 2. Hole and Electron Mobilities, Threshold Voltages (Vth), and Ion/Ioff Ratios for FETs on Thin Films of DPPA1, DPPA2, and DPPA3 with OTS-Modified SiO2/Si Substrates and Unmodified Au as Electrodes at Different Annealing Temperatures polymer DPPA1

DPPA2

DPPA3

a

temp (°C) 25 80 120 160 25 80 120 25 80 120 160

μha (cm2 V−1 s−1)

Vth,h (V)

Ion/Ioff

0.12/0.09 0.33/0.22 0.97/0.82 0.36/0.25 0.03/0.02 0.08/0.06 0.02/0.01 0.01/0.008 0.03/0.023 0.062/0.054 0.04/0.029

−4 to 3 0 to 7 −7 to 6 −1 to 4 −4 to 1 −3 to 3 0 to 4 −10 to 0 −12 to −2 −5 to −12 −9 to 10

10 −10 104−105 104−105 104−105 102−103 102 102 103 103−104 103 103−104 4

μea (cm2 V−1 s−1)

Vth,e (V)

Ion/Ioff

2.4 × 10−3/2.0 × 10−3 6.7 × 10−3/5.3 × 10−3 0.021/0.016 7.8 × 10−3/5.9 × 10−3

26−48 39−53 42−51 46−61

10−102 102 10−102 102

5

The mobilities were provided in “highest/average’’ form, and the performance data were obtained based on more than 10 different FETs.

Figure 4. AFM images (up) and XRD patterns (bottom) of thin films of DPPA1 (a), DPPA2 (b), and DPPA3 (c) deposited on OTS-modified SiO2/Si substrates at room temperature and after thermal annealing.

Figure 5. J−V curves (left) and IPCE (right) spectra of the OPV devices based on blending thin films of polymer:PC71BM under AM 1.5 illumination (100 mW/cm2).

formed after thermal annealing of thin films of DPPA1 at 120 °C. Similarly, part of molecular domains emerged to yield large domains after thermal annealing for thin film of DPPA3. But, thin film morphology kept almost unaltered for DPPA2 after thermal annealing. These morphological variations after thermal annealing are consistent with the observation that charge mobilities increased after thermal annealing, in particular for thin films of DPPA1 and DPPA3. Figure 4 shows the out-of-plane and in-plane X-ray diffraction patterns of thin films of DPPA1, DPPA2, and DPPA3 before and after thermal annealing. It is clear that only

and electron mobilities started to decrease after further annealing at higher temperature. Thin films of DPPA1, DPPA2, and DPPA3 before and after thermal annealing were characterized by atomic force microscopy (AFM) and grazing incidence X-ray diffraction (GIXRD). Figure 4 shows AFM images of the as-prepared thinfilms of DPPA1, DPPA2, and DPPA3 and those after thermal annealing. The root-mean-square roughness (RRMS) was changed from 0.330 to 0.425 nm for DPPA1, 0.270 to 0.490 nm for DPPA2, and 0.404 to 0.377 nm for DPPA3 after thermal annealing. Large domains of sizes ca. 30 nm were E

DOI: 10.1021/acs.macromol.5b00158 Macromolecules XXXX, XXX, XXX−XXX

Macromolecules rather weak diffraction signals were detected for the as-prepared thin films of DPPA1, DPPA2, and DPPA3. For instance, three weak diffraction signals at around 2θ = 4.7° (out of plane), 2θ = 21.6° (broad, out of plane), and 2θ = 4.4° (in plane) were detected for the as-prepared thin film of DPPA1. Thus, they could be regarded as amorphous thin films. After thermal annealing at 120 °C the intensity of the signals at around 2θ = 4.7° and 2θ = 4.4° were enhanced, and a new broad diffraction signal at around 2θ = 21.4° (broad, in plane) emerged for thin film of DPPA1. Diffraction signals at around 2θ = 4.4° (out of plane), 2θ = 4.0° (in plane), and 2θ = 21.7° (broad, in plane) were detected for thin film of DPPA3 after thermal annealing at 120 °C. But the diffraction pattern of thin film of DPPA2 was almost not changed after thermal annealing. These AFM and XRD data agree with the observation that charge mobilities of thin films of DPPA1 and DPPA3 increase obviously after thermal annealing, whereas hole mobility of thin film of DPPA2 is just slightly enhanced (see Table 2). Photovoltaic Device Performance. Judging from their HOMO/LUMO levels and absorption spectra, DPPA1, DPPA2, and DPPA3 may function as electron donors for photovoltaic materials. Blending thin films of DPPA1, DPPA2, and DPPA3 with PC71BM at different weight ratios were employed as active layers for fabrication of OPVs with the configuration of ITO/PEDOT:PSS/active layer/Ca/Al. Figure 5 shows the J−V curves for OPVs with the respective blending thin films of DPPA1, DPPA2, and DPPA3 with PC71BM at 1:1.5 weight ratio and the corresponding IPCE spectra. The photovoltaic performance data are summarized in Table 3. The

ratio (w:w)

Jsc (mA/cm2)

Voc (V)

FF

PCE (%)

DPPA1/PC71BM DPPA2/PC71BM DPPA3/PC71BM

1:1.5b 1:1.5b 1:1.5b

5.61 1.37 1.56

0.54 0.47 0.63

0.67 0.41 0.41

2.04/1.92c 0.26/0.22c 0.40/0.33c

CONCLUSIONS

■

EXPERIMENTAL SECTION

Materials and Characterization Techniques. The reagents and starting materials were commercially available and used without any further purification, if not specified elsewhere. Compounds 1, 3, and 7 were synthesized according to the previous report.16b,17 1 H NMR and 13C NMR spectra were recorded on Bruker AVANCE III 400 and 300 MHz spectrometers. Elemental analysis was performed on a Carlo Erba model 1160 elemental analyzer. UV−vis absorption spectra were measured with JASCO V-570 UV−vis spectrophotometer. Gel permeation chromatography (GPC) analysis was performed on an PL-GPC 220 high temperature chromatograph at 150 °C equipped with a IR5 detector; polystyrene was used as the calibration standard and 1,2,4-trichlorobenzene as eluent; the flow rate was 1.0 mL/min. Thermogravimetric analysis (TGA) and differential thermal analysis (DSC) were carried out on a SHIMADZU DTG-60 instruments under a dry nitrogen flow; the heating was carried out from room temperature to 550 °C with a heating rate of 10 °C/min. The GIXRD data were measured at 1W1A, Beijing Synchrotron Radiation Facility. The thin film surfaces were examined by tappingmode AFM using Digital Instruments Nanoscope V atomic force microscope under ambient conditions in the dark. Cyclic voltammetric measurements were carried out in a conventional three-electrode cell using a Pt working electrode, a Pt counter electrode, and a Ag/AgCl (saturated KCl) reference electrode on a computer-controlled CHI660C instruments at room temperature; the scan rate was 100 mV s−1, and n-Bu4NPF6 (0.1 M) in CH3CN was used as the supporting electrolyte. For calibration, the redox potential of ferrocene/ferrocenium (Fc/Fc+) was measured under the same conditions (see Figure S2). The onset oxidation and reduction potentials were presented by reference to the redox potential of ferrocene/ferrocenium (Fc/Fc+). Synthesis of 1,3-Bis(5-bromothiophen-2-yl)azulene (2). Compound 1 (1.0 mmol, 292.4 mg) and N-bromosuccinimide (NBS) (2.0 mmol, 356.0 mg) were dissolved in 50 mL of anhydrous CHCl3. The reaction mixture was then cooled to −78 °C and stirred 3.0 h under N2. After returning to room temperature, 25 mL of water was added, and the mixture was extracted with 25 mL of CHCl3 for three times, dried over MgSO4, and filtered. Then, the filtrate was concentrated under reduced pressure. The crude product was purified by column chromatography with petroleum ether (60−90 °C) as

The data were based on more than 10 devices. bAs-casted thin films. Data were provided in “highest/average” form.

a c

■

In this paper, three new conjugated D−A copolymers DPPA1, DPPA2, and DPPA3, entailing azulene as electron donor and DPP as electron acceptor, were synthesized, and their semiconducting properties were studied. By incorporation of different regioisomeric azulene in the main chain, optoelectronic properties of three polymers were successfully modulated. Thin films of DPPA1 and DPPA2, in which fivemembered ring of azulene is connected with DPP, exhibit ptype semiconducting behavior with hole mobilities up to 0.97 cm2 V−1 s−1, whereas thin film of DPPA3 with sevenmembered ring of azulene in the conjugated backbone behaves as ambipolar semiconductor with hole and electron mobilities reaching 0.062 and 0.021 cm 2 V −1 s −1 , respectively. Furthermore, DPPA1 can function as electron donor for organic photovoltaic cells, and power conversion efficiency (PCE) of the blending thin film of DPPA1 and PC71BM reaches 2.04%. Current studies demonstrate that azulene, a nonalternant aromatic hydrocarbon with high dipole moment, can be utilized to construct conjugated D−A polymers for high performance semiconductors. Further investigations include the design and synthesis of more conjugated frameworks containing azulene with lower HOMO/LUMO levels and strong absorptions to improve their semiconducting and photovoltaic performances.

Table 3. Optimized Photovoltaic Performances of Blending Films of DPPA1, DPPA2, and DPPA3 with PC71BMa donor:acceptor

Article

results manifest that the blending thin film of DPPA1:PC71BM at 1:1.5 weight ratio exhibits the best photovoltaic performance with a maximum PCE of 2.04%. But, PCEs of the respective PVCs with blending thin films of DPPA2:PC71BM and DPPA3:PC71BM are rather low. This agrees well with the observation that DPPA1 shows higher IPCE than DPPA2 and DPPA3. Unfortunately, thermal annealing, introduction of additives, and variation of donor/acceptor ratios could not obviously improve the photovoltaic performances under current device configuration. The low PCEs for DPPA2:PC71BM and DPPA3:PC71BM blending thin films may be attributed to their poor morphologies. As depicted in Figure S3, large domains with sizes over 300 nm were formed for blending thin films of DPPA2:PC71BM and DPPA3:PC71BM. In comparison, sizes of domains of DPPA1:PC71BM were found to be smaller (ca. 200 nm). Additionally, the relatively large local dipole moment of DPPA1 may be beneficial for charge separation and thus for better photovoltaic performance.21 The relative high Voc for PVC with DPPA3:PC71BM is consistent with the fact that the HOMO energy of DPPA3 is relative low compared to those of DPPA1 and DPPA2 (see Table 3). F

DOI: 10.1021/acs.macromol.5b00158 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules

mol−1. Anal. Calcd for (C64H92N2O2S2)n: C, 77.99; H, 9.41; N, 2.84; S, 6.51. Found: C, 77.39; H, 9.25; N, 2.88; S, 6.43. Fabrication of FET Devices. Bottom-gate/bottom-contact FETs were fabricated. A heavily doped n-type Si wafer and a layer of dry oxidized SiO2 (300 nm, with roughness lower than 0.1 nm and capacitance of 11 nF cm−2) were used as a gate electrode and gate dielectric layer, respectively. The drain-source (D-S) gold contacts were fabricated by photolithography. The substrates were first cleaned by sonication in acetone and water for 5.0 min and immersed in piranha solution (2:1 mixture of sulfuric acid and 30% hydrogen peroxide) for 20 min. This was followed by rinsing with deionized water and isopropyl alcohol for several times, and it was blow-dried with nitrogen. Then, the surface was modified with n-octadecyltrichlorosilane (OTS). After that, the substrates were cleaned in nhexane, CHCl3, and isopropyl alcohol. The films of DPPA1, DPPA2, and DPPA3 were fabricated by spin-coating their CHCl3 solutions (5.0 mg/mL) at 2000 rpm. The annealing process was carried out in vacuum for 1.0 h at each temperature. Field-effect characteristics of the devices were determined in nitrogen using a Keithley 4200 SCS semiconductor parameter analyzer. The mobility of the OFETs in the saturation region was extracted from the equation

eluent. Compound 2 was obtained as green solids (70.0 mg, 15.6%). 1 H NMR (CDCl3, 400 MHz): δ 8.63 (d, 2H, J = 10 Hz), 8.01 (s, 1H), 7.64 (t, 1H, J = 9.8 Hz), 7.21 (t, 2H, J = 9.8 Hz), 7.13 (d, 2H, J = 4 Hz), 7.02 (d, 2H, J = 3.6 Hz). 13C NMR (CDCl3, 100 MHz): δ 140.25, 140.04, 137.19, 136.58, 136.44, 130.60, 125.42, 124.93, 122.23, 111.19. EI m/z: 450 [M+]. Anal. Calcd for C18H10S2Br2: C, 48.02; H, 2.24; S, 14.24. Found: C, 47.72; H, 2.35; S, 14.05. Synthesis of 1,3-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan2-yl)azulene (4). Compound 3 (3.6 mmol, 1.03 g), 4,4,4′,4′,5,5,5′,5′octamethyl-2,2′-bi(1,3,2-dioxaborolane) (9.0 mmol, 2.29 g), KOAc (21.6 mmol, 2.12 g), and a catalytic amount of [1,1′-bis(diphenylphosphino)ferrocene]palladium(II) chloride (Pd(dppf)2Cl2· CH2Cl2) (0.72 mmol, 588.0 mg) were dissolved in 100 mL of anhydrous 1,4-dioxane. The reaction mixture was then heated at 80 °C and stirred overnight under N2. After cooling to room temperature, the solvent was removed under reduced pressure. The crude product was purified by column chromatography with petroleum ether (60−90 °C) and CH2Cl2 (7:3, v/v) as the eluent. Compound 4 was obtained as dark red solids (92 mg, 7.15%). 1H NMR (CDCl3, 400 MHz): δ 9.17 (d, 2H, J = 10 Hz), 8.83 (s, 1H), 7.72 (t, 1H, J = 9.6 Hz), 7.47 (t, 2H, J = 9.6 Hz), 1.39 (s, 24H). 13C NMR (CDCl3; 75 MHz): δ 155.57, 151.28, 138.35, 137.78, 126.92, 83.08, 25.18. EI m/z: 360 [M+]. Anal. Calcd for C22H30B2O4: C, 69.52; H, 7.96. Found: C, 69.61; H, 7.90. General Synthetic Procedures for DPPA1, DPPA2, and DPPA3. Compound 5 (1.0 equiv) or compound 6 (1.0 equiv), the corresponding azulene derivatives (1.0 equiv), and P(o-tol)3 (0.16 equiv) were dissolved in the mixture of toluene (10 mL) and K2CO3 (2.0 M, 2.0 mL). The solution was purged with N2 for 30 min, followed by addition of Pd2(dba)3 (0.02 equiv). The reaction mixture was stirred at 90 °C for 48 h. The resulting mixture was poured into methanol and stirred for 3.0 h. The dark precipitate was filtered off and subjected to Soxhlet extraction for 2 days successively with methanol, hexane, and acetone to remove oligomers and the remaining catalyst. The resulting polymer was extracted with chloroform and precipitated again from methanol, filtered, washed with methanol, and dried under vacuum at 50 °C for 48 h. Synthesis of DPPA1. Compound 3 (58.5 mg, 0.13 mmol), compound 6 (144.7 mg, 0.13 mmol), P(o-tol)3 (6.4 mg, 0.021 mmol), and Pd2(dba)3 (2.4 mg, 0.0026 mmol) were used. The purified polymer was collected to give deep blue solid (100.0 mg, 66.9% yield). 1 H NMR (400 MHz, CDCl3) δ: 8.59−8.86 (m, br, 2H), 8.58−8.53 (m, br, 3H), 8.05−7.86 (m, br, 1H), 7.59−7.52 (m, br, 1H), 7.18−7.13 (m, br, 7H), 4.02 (m, br, 4H), 1.96 (m, br, 2H), 1.57−1.21 (m, br, 64H), 0.83 (m, br, 12H). 13C NMR (100 MHz; solid) δ: 160.84, 136.99, 131.64, 126.70, 124.10, 108.16, 45.24, 39.06, 30.97, 23.77, 15.20. Mw/Mn (GPC) = 41.7/12.3 kg mol−1. Anal. Calcd for (C72H96N2O2S4)n: C, 75.21; H, 8.42; N, 2.44; S, 11.15. Found: C, 74.01; H, 8.43; N, 2.36; S, 11.10. Synthesis of DPPA2. Compound 3 (31.5 mg, 0.11 mmol), compound 6 (122.5 mg, 0.11 mmol), P(o-tol)3 (5.4 mg, 0.018 mmol), and Pd2(dba)3 (2.0 mg, 0.0022 mmol) were used. The purified polymer was collected to give deep blue solid (84.3 mg, 77.8% yield). 1 H NMR (300 MHz; CDCl3) δ: 8.99−8.75 (m, br, 3H), 7.95−7.88 (m, br, 2H), 7.74−7.36 (m, 5H), 4.12−4.09 (m, br, 4H), 2.24−2.02 (m, br, 2H), 1.59−1.20 (m, br, 64H), 0.82 (m, br, 12H). 13C NMR (100 MHz; solid) δ: 160.97, 141.81, 137.07, 129.15, 127.29, 124.66, 108.28, 37.99, 30.74, 23.64, 14.98. Mw/Mn (GPC) = 38.1/14.3 kg· mol−1. Anal. Calcd for (C64H92N2O2S2)n: C, 77.99; H, 9.41; N, 2.84; S, 6.51. Found: C, 77.23; H, 9.77; N, 2.82; S, 6.29. Synthesis of DPPA3. Compound 4 (106.4 mg, 0.28 mmol), compound 5 (285.4 mg, 0.28 mmol), P(o-tol)3 (13.7 mg, 0.045 mmol), and Pd2(dba)3 (5.1 mg, 0.0056 mmol) were used. The purified polymer was collected to give deep green solid (170 mg, 61.6% yield). 1 H NMR (400 MHz; CDCl3) δ: 9.11−8.80 (m, br, 2H), 7.95−7.44 (m, br, 8H), 4.11−4.03 (m, br, 4H), 2.03−2.02 (m, br, 2H), 1.57−1.20 (m, br, 64H), 0.82 (m, br, 12H). 13C NMR (100 MHz; solid) δ: 161.07, 150.42, 148.84, 138.16, 133.17, 129.97, 126.63, 123.93, 108.99, 45.66, 38.95, 30.72, 23.61, 14.94. Mw/Mn (GPC) = 49.4/15.0 kg

IDS =

W μCi(VGS − Vth)2 2L

where IDS is the drain electrode collected current, L and W are the channel length and width, respectively, μ is the mobility of the device, Ci is the capacitance per unit area of the gate dielectric layer, VGS is the gate voltage, and Vth is the threshold voltage. The Vth of the device was determined by extrapolating the (IDS,sat)1/2 vs VGS plot to IDS = 0. Fabrication of Organic Photovoltaic Cells. OPVs were fabricated with ITO as the positive electrode and Al as the negative electrode. The patterned indium tin oxide (ITO) glass (sheet resistance = 15 Ω−1) was precleaned in an ultrasonic bath in detergent, deionized water, acetone, and isopropyl alcohol and then treated in an ultraviolet-ozone chamber (Jelight Company, USA) for 30 min. A thin layer (30 nm) of poly(3,4ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS, Baytron PVP AI 4083, Germany) was spin-coated onto the ITO glass and baked at 150 °C for 15 min. An o-dichlorobenzene solution with a concentration of 15 mg/mL of each polymer (DPPA1, DPPA2, and DPPA3) with PC71BM was subsequently spin-coated on the PEDOT:PSS layer to form the active layer. The thickness (ca. 100− 120 nm) of the active layer was measured using an Ambios Technology XP-2 profilometer. Ca (ca. 20 nm) and aluminum layer (ca. 70 nm) were then evaporated onto the surface of the active layer under vacuum (ca. 10−5 Pa) to form the negative electrode, respectively. The active area of the device was 4.0 mm2. The J−V curves were measured with a computer-controlled Keithley 236 Source Measure Unit. A xenon lamp coupled with AM1.5 solar spectrum filters was used as the light source, and the optical power at the sample was 100 mW cm−2. The incident photon to converted current efficiency (IPCE) spectra was measured using a Stanford Research Systems model SR830 DSP lock-in amplifier coupled with a WDG3 monochromator and a 500 W xenon lamp.

■

ASSOCIATED CONTENT

S Supporting Information *

TGA, DSC, cyclic voltammograms, density functional theory (DFT) calculations, characterization of OPVs, 1H NMR, and 13 C NMR data. This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Authors

*E-mail [email protected] (D.Z.). *E-mail [email protected] (Z.L.). G

DOI: 10.1021/acs.macromol.5b00158 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules Notes

Furlan, A.; Roelofs, W. S. C.; Wienk, M. M.; Janssen, R. A. J. J. Am. Chem. Soc. 2013, 135, 18942. (6) Li, J.; Zhao, Y.; Tan, H. S.; Guo, Y. L.; Di, C.-A.; Yu, G.; Liu, Y. Q.; Lin, M.; Lim, S. H.; Zhou, Y.; Su, H.; Ong, B. S. Sci. Rep. 2012, 2, 754. (7) (a) Lee, J.; Han, A.-R.; Kim, J.; Kim, Y.; Oh, J. H.; Yang, C. J. Am. Chem. Soc. 2012, 134, 20713. (b) Lee, J.; Han, A.-R.; Yu, H.; Shin, T. J.; Yang, C.; Oh, J. H. J. Am. Chem. Soc. 2013, 135, 9540. (8) (a) Yan, H.; Chen, Z.; Zheng, Y.; Newman, C.; Quinn, J. R.; Dötz, F.; Kastler, M.; Facchetti, A. Nature 2009, 457, 679. (b) Zhan, X. W.; Tan, Z. A.; Domercq, B.; An, Z.; Zhang, X.; Barlow, S.; Li, Y. F.; Zhu, D. B.; Kippelen, B.; Marder, S. R. J. Am. Chem. Soc. 2007, 129, 7246. (c) Gu, C. L.; Hu, W. P.; Yao, J. N.; Fu, H. B. Chem. Mater. 2013, 25, 2178. (d) Li, Y. H.; Zhang, G. X.; Liu, Z. T.; Chen, X.; Wang, J. G.; Di, C.-A.; Zhang, D. Q. Macromolecules 2013, 46, 5504. (9) (a) Lei, T.; Wang, J.-Y.; Pei, J. Acc. Chem. Res. 2014, 47, 1117. (b) Mei, J. G.; Kim, D. H.; Ayzner, A. L.; Toney, M. F.; Bao, Z. N. J. Am. Chem. Soc. 2011, 133, 20130. (10) (a) Yuen, J. D.; Fan, J.; Seifter, J.; Lim, B.; Hufschmid, R.; Heeger, A. J.; Wudl, F. J. Am. Chem. Soc. 2011, 133, 20799. (b) Tsao, H. N.; Cho, D. M.; Park, I.; Hansen, M. R.; Mavrinskiy, A.; Yoon, D. Y.; Graf, R.; Pisula, W.; Spiess, H. W.; Müllen, K. J. Am. Chem. Soc. 2011, 133, 2605. (c) Li, Y.; Zou, J.; Yip, H.-L.; Li, C.-Z.; Zhang, Y.; Chueh, C.-C.; Intemann, J.; Xu, Y.; Liang, P.-W.; Chen, Y.; Jen, A. K.Y. Macromolecules 2013, 46, 5497. (11) (a) Cai, Z. X.; Luo, H. W.; Qi, P. L.; Wang, J. G.; Zhang, G. X.; Liu, Z. T.; Zhang, D. Q. Macromolecules 2014, 47, 2899. (b) Cai, Z. X.; Liu, Z. T.; Luo, H. W.; Qi, P. L.; Zhang, G. X.; Zhang, D. Q. Chin. J. Chem. 2014, 32, 788. (c) Wang, J. G.; Chen, X.; Cai, Z. X.; Luo, H. W.; Li, Y. H.; Liu, Z. T.; Zhang, G. X.; Zhang, D. Q. Polym. Chem. 2013, 4, 5283. (12) Price, S. C.; Stuart, A. C.; You, W. Macromolecules 2010, 43, 797. (13) (a) Bijleveld, J. C.; Gevaerts, V. S.; Nuzzo, D. D.; Turbiez, M.; Mathijssen, S. G. J.; Leeuw, D. M. D.; Wienk, M. M.; Janssen, R. A. J. Adv. Mater. 2010, 22, E242. (b) Sonar, P.; Singh, S. P.; Li, Y. N.; Ooi, Z.-E.; Ha, T.-J.; Wong, I.; Soh, M. S.; Dodabalapur, A. Energy Environ. Sci. 2011, 4, 2288. (14) Wang, F. K.; Lin, T. T.; He, C. B.; Chi, H.; Tang, T.; Lai, Y.-H. J. Mater. Chem. 2012, 22, 10448. (15) (a) Yamaguchi, Y.; Maruya, Y.; Katagiri, H.; Nakayama, K.-I.; Ohba, Y. Org. Lett. 2012, 14, 2316. (b) Yamaguchi, Y.; Ogawa, K.; Nakayama, K.-I.; Ohba, Y.; Katagiri, H. J. Am. Chem. Soc. 2013, 135, 19095. (16) (a) Wang, F.; Lai, Y.-H.; Kocherginsky, N. M.; Kosteski, Y. Y. Org. Lett. 2003, 5, 995. (b) Wang, F.; Lai, Y. H.; Han, M. Y. Macromolecules 2004, 37, 3222. (c) Wang, X.; Ng, J. K. P.; Jia, P.; Lin, T.; Cho, C. M.; Xu, J.; Lu, X.; He, C. Macromolecules 2009, 42, 5534. (d) Ding, G.; Cho, C. M.; Chen, C.; Zhou, D.; Wang, X.; Tan, A. Y. X.; Xu, J.; Lu, X. Org. Electron. 2013, 14, 2748. (e) Tsurui, K.; Murai, M.; Ku, S.-Y.; Hawker, C. J.; Bobb, M. J. Adv. Funct. Mater. 2014, 24, 7338. (f) Puodziukynaite, E.; Wang, H. W.; Lawrence, J.; Wise, A. J.; Russell, T. P.; Barnes, M. D.; Emrick, T. J. Am. Chem. Soc. 2014, 136, 11043. (g) Umeyama, T.; Watanabe, Y.; Miyata, T.; Imahori, H. Chem. Lett. 2015, 1, 47. (h) Amir, E.; Amir, R. J.; Campos, L. M.; Hawker, C. J. J. Am. Chem. Soc. 2011, 133, 10046. (i) Murai, M.; Amir, E.; Amir, R. J.; Hawker, C. J. Chem. Sci. 2012, 3, 2721. (j) Lim, S. Z. H.; Neo, W. T.; Cho, C. M.; Wang, X.; Tan, A. Y. X.; Chan, H. S. O.; Xu, J. Aust. J. Chem. 2013, 66, 1048. (k) Amir, E.; Murai, M.; Amir, R. J.; Cowart, J. S., Jr.; Chabinyc, M. L.; Hawker, C. J. Chem. Sci. 2014, 5, 4483. (17) Anderson, A. G., Jr.; Nelson, J. A.; Tazuma, J. J. J. Am. Chem. Soc. 1953, 75, 4980. (18) (a) Sun, Z.; Lee, S.; Park, K. H.; Zhu, X.; Zhang, W.; Zheng, B.; Hu, P.; Zeng, Z.; Das, S.; Li, Y.; Chi, C.; Li, R.-W.; Huang, K.-W.; Ding, J.; Kim, D.; Wu, J. J. Am. Chem. Soc. 2013, 135, 18229. (b) Intemann, J. J.; Yao, K.; Yip, H.-L.; Xu, Y.-X.; Li, Y.-X.; Liang, P.W.; Ding, F.-Z.; Li, X.; Jen, A. K.-Y. Chem. Mater. 2013, 25, 3188. (c) Chang, H.-H.; Tsai, C.-E.; Lai, Y.-Y.; Liang, W.-W.; Hsu, S.-L.; Hsu, C.-S.; Cheng, Y.-J. Macromolecules 2013, 46, 7715. (d) Cardona,

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The present research was financially supported by Chinese Academy of Sciences, NSFC, and State Key Basic Research Program. The authors thank Prof. Yongfang Li for allowance for using the facility for fabrication of OPVs. The authors also gratefully acknowledge the assistance of scientists of Diffuse Xray Scattering Station at Beijing Synchrotron Radiation Facility for measuring the GIXRD data.

■

REFERENCES

(1) (a) Murphy, A. R.; Fréchet, J. M. J. Chem. Rev. 2007, 107, 1066. (b) Schmidt, R.; Oh, J. H.; Sun, Y.-S.; Deppisch, M.; Krause, A.-M.; Radacki, K.; Braunschweig, H.; Könemann, M.; Erk, P.; Bao, Z. N.; Würthner, F. J. Am. Chem. Soc. 2009, 131, 6215. (c) Cao, Y.; Steigerwald, M. L.; Nuckolls, C.; Guo, X. Adv. Mater. 2010, 22, 20. (d) Li, L.; Gao, P.; Schuermann, K. C.; Ostendorp, S.; Wang, W.; Du, C.; Lei, Y.; Fuchs, H.; De Cola, L.; Müllen, K.; Chi, L. J. Am. Chem. Soc. 2010, 132, 8807. (e) Li, Y. F. Acc. Chem. Res. 2012, 45, 723. (f) Liang, Y. Y.; Wu, Y.; Feng, D. Q.; Tsai, S.-T.; Son, H.-J.; Li, G.; Yu, L. P. J. Am. Chem. Soc. 2009, 131, 56. (g) Lei, T.; Cao, Y.; Fan, Y. L.; Liu, C.-J.; Yuan, S.-C.; Pei, J. J. Am. Chem. Soc. 2011, 133, 6099. (2) (a) Liang, Z.; Tang, Q.; Mao, R.; Liu, D.; Xu, J.; Miao, Q. Adv. Mater. 2011, 23, 5514. (b) Anthony, J. E.; Facchetti, A.; Heeney, M.; Marder, S. R.; Zhan, X. W. Adv. Mater. 2010, 22, 3876. (c) Rochat, S.; Swager, T. M. J. Am. Chem. Soc. 2013, 135, 17703. (d) Mitsui, C.; Soeda, J.; Miwa, K.; Tsuji, H.; Takeya, J.; Nakamura, E. J. Am. Chem. Soc. 2012, 134, 5448. (e) Liu, Z. T.; Zhang, G. X.; Cai, Z. X.; Chen, X.; Luo, H. W.; Li, Y. H.; Wang, J. G.; Zhang, D. Q. Adv. Mater. 2014, 26, 6965. (f) Sirringhaus, H. Adv. Mater. 2014, 26, 1319. (g) Müller, C.; Zhigadol, N. D.; Kumar, A.; Baklar, M. A.; Karpinski, J.; Smith, P.; Kreouzis, T.; Stinglin, N. Macromolecules 2011, 44, 1221. (3) (a) Takeda, Y.; Andrew, T.; Lobez, J.; Mork, A.; Swager, T. M. Angew. Chem., Int. Ed. 2012, 51, 9042. (b) Wang, C.; Dong, H.; Hu, W. P.; Liu, Y. Q.; Zhu, D. B. Chem. Rev. 2012, 112, 2208. (c) He, T.; Stolte, M.; Würthner, F. Adv. Mater. 2013, 25, 6951. (d) Li, L.; Gao, P.; Baumgarten, M.; Müllen, K.; Lu, N.; Fuchs, H.; Chi, L. Adv. Mater. 2013, 25, 3419. (e) Li, K.; Li, Z.; Feng, K.; Xu, X.; Wang, L.; Peng, Q. J. Am. Chem. Soc. 2013, 135, 13549. (f) Hou, J. H.; Chen, H.-Y.; Zhang, S. Q.; Chen, R. I.; Yang, Y.; Wu, Y.; Li, G. J. Am. Chem. Soc. 2009, 131, 15586. (4) (a) Liu, Y.-Y.; Song, C.-L.; Zeng, W.-J.; Zhou, K.-G.; Shi, Z.-F.; Ma, C.-B.; Yang, F.; Zhang, H.-L.; Gong, X. J. Am. Chem. Soc. 2010, 132, 16349. (b) Lee, T.-H.; Wu, K.-Y.; L, T.-Y.; Wu, J.-S; Wang, C.-L.; Hsu, C.-S. Macromolecules 2013, 46, 7687. (c) 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. J. Adv. Mater. 2014, 26, 2993. (d) Luo, C.; Kyaw, A. K. K.; Perez, L. A.; Patel, S.; Wang, M.; Grimm, B.; Bazan, G. C.; Kramer, E. J.; Heeger, A. J. Nano Lett. 2014, 14, 2764. (e) Chen, H.-Y.; Hou, J. H.; Zhang, S. H.; Liang, Y. Y.; Yang, G. W.; Yang, Y.; Yu, L. P.; Wu, Y.; Li, G. Nat. Photonics 2009, 3, 649. (f) Zhang, M. J.; Guo, X.; Zhang, S. Q.; Huo, L. J.; Ade, H.; Hou, J. H. Adv. Mater. 2014, 26, 1118. (g) Zhou, P. C.; Zhang, Z. G.; Li, Y. F.; Chen, X. G.; Qin, J. G. Chem. Mater. 2014, 26, 3495. (h) Huo, L. J.; Zhang, S. Q.; Guo, X.; Xu, F.; Li, Y. F.; Hou, J. H. Angew. Chem., Int. Ed. 2011, 50, 9697. (i) Gao, X.; Hu, Y. J. Mater. Chem. C 2014, 2, 3099. (j) Biniek, L.; Schroeder, B. C.; Nielsen, C. B.; McCulloch, I. J. Mater. Chem. 2012, 22, 14803. (5) (a) Nielsen, C. B.; Turbiez, M.; McCulloch, I. Adv. Mater. 2013, 25, 1859. (b) Li, Y.; Sonar, P.; Murphy, L.; Hong, W. Energy Environ. Sci. 2013, 6, 1684. (c) Dou, L.; Gao, J.; Richard, E.; You, J.; Chen, C. C.; Cha, K. C.; He, Y.; Li, G.; Yang, Y. J. Am. Chem. Soc. 2012, 134, 10071. (d) Qu, S. Y.; Tian, H. Chem. Commun. 2012, 48, 3039. (e) Walker, B.; Liu, J. H.; Kim, C.; Welch, G. C.; Park, J. K.; Lin, J.; Zalar, P.; Proctor, C. M.; Seo, J. H.; Bazan, G. C.; Nguyen, T.-Q. Energy Environ. Sci. 2013, 6, 952. (f) Li, W. W.; Hendriks, K. H.; H

DOI: 10.1021/acs.macromol.5b00158 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules C. M.; Kaifer, A. E.; Stockdale, D.; Bazan, G. C. Adv. Mater. 2011, 23, 2367. (19) (a) Cai, Z. X.; Guo, Y. L.; Yang, S. F.; Peng, Q.; Luo, H. W.; Liu, Z. T.; Zhang, G. X.; Liu, Y. Q.; Zhang, D. Q. Chem. Mater. 2013, 25, 471. (b) Lei, T.; Dou, J.-H.; Ma, Z.-J.; Yao, C.-H.; Liu, C.-J.; Wang, J.Y.; Pei, J. J. Am. Chem. Soc. 2012, 134, 20025. (c) Lei, T.; Xia, X.; Wang, J.-Y.; Liu, C.-J.; Pei, J. J. Am. Chem. Soc. 2014, 136, 2135. (20) The respective output curves of DPPA2 were not ideal. This is probably owing to the relatively large contact resistance. The transfer curve from which the charge mobility was deduced was yielded at VDS = −100 V. (21) The calculated dipole moments of the repeated units of DPPA1, DPPA2, and DPPA3 were 3.33, 3.41, and 0.88 D, respectively.

I

DOI: 10.1021/acs.macromol.5b00158 Macromolecules XXXX, XXX, XXX−XXX