Synthesis and Characterization of Isoindigo[7,6-g]isoindigo-Based

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Synthesis and Characterization of Isoindigo[7,6‑g]isoindigo-Based Donor−Acceptor Conjugated Polymers Yu Jiang,†,§ Yao Gao,†,§ Hongkun Tian,*,† Junqiao Ding,*,† Donghang Yan,† Yanhou Geng,*,†,‡ and Fosong Wang† †

State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, P. R. China ‡ School of Material Science and Engineering and Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin University, Tianjin 300072, P. R. China § University of Chinese Academy of Sciences, Beijing 100049, P. R. China S Supporting Information *

ABSTRACT: Four donor (D)−acceptor (A) conjugated polymers with isoindigo[7,6-g]isoindigo ([3E,8E]-3,8-bis(2-oxoindolin-3-ylidene)-6,8-dihydroindolo[7,6-g]indole-2,7(1H,3H)-dione, DIID) as A-unit and thiophene derivatives as D-units were synthesized by Stille polycondensation. Optical and electrochemical properties of the polymers were studied by UV−vis− NIR absorption spectrometer and cyclic voltammetry. Compared with isoindigo-based analogues, the polymers display much broader absorption spectra (covering 400−950 nm) and remarkably lower bandgaps (ca. 1.3 eV). All polymers showed ambipolar transport properties as evaluated by bottom-gate/top-contact (BGTC) and top-gate/bottom-contact (TGBC) organic thin film transistors (OTFTs) in air. Gate-voltage-dependent hole mobility (μh) was observed for BGTC devices, while the mobility of TGBC devices exhibited weak gate-voltage dependence. P3 delivered the best device performance. At the optimized thermal annealing temperature (200 °C), a μh of 1.79 cm2/(V s) and an electron mobility (μe) of 0.087 cm2/(V s) were demonstrated with BGTC devices, and μh calculated from the higher VGS region is decreased to 0.35 cm2/(V s). The relatively balanced hole and electron mobilities were observed for TGBC devices based on P3, which were 0.45 and 0.16 cm2/(V s), respectively.

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INTRODUCTION Conjugated polymers have been widely used as semiconductors in organic thin film transistors (OTFTs). Compared with amorphous silicon-based thin film transistors, polymer-based OTFTs have many advantages such as low cost and flexible and large-area production because of their good mechanical property and solution processability.1−8 Donor−acceptor (D−A) conjugated polymers are characterized by strong intermolecular interaction and easy modulation of energy levels via appropriately selecting Dand A-units. These features allow feasibly achieving low bandgap and targeting high hole or/and electron mobility. Therefore, D−A conjugated polymers have become the most promising semiconducting materials today, and various highmobility D−A conjugated polymers have been synthesized by using different D- and A-units.1,9−11 It is known that D- and Aunits are equally important for adjusting the properties of D−A conjugated polymers. However, compared to D-units, less Aunits have been explored to date because the synthesis of electron-deficient aromatics is generally more difficult and usually needs developing new protocol.5,12−17 Therefore, the development of new electron-deficient aromatics is highly © XXXX American Chemical Society

desirable especially while considering their importance on tuning the lowest unoccupied molecular orbital (LUMO) levels of semiconducting polymers for realizing ambipolar or n-type transport.4,7,18−21 Isoindigo (IID) is a well-studied A-unit featured with strong electron deficiency and coplanarity.22−25 Since Pei and coworkers reported the first IID based D−A conjugated polymers with hole mobility over 0.7 cm2/(V s) in 2011,26 it has become one of the most important A-units for constructing high mobility conjugated polymers, and the field-effect hole mobility close to 4 cm2/(V s) has been demonstrated via side chain engineering.27 Moreover, ambipolar D−A conjugated polymers can be obtained by introducing fluorine or chlorine atoms in IID framework.28,29 Alternatively, extending the conjugation length of IID unit can result in new electron-deficient units. As shown in Chart 1, all three IID derivatives with extended conjugation, which are named as BDOPV, NBDOPV, and INDF, exhibited deeper LUMOs and lower bandgaps Received: January 2, 2016 Revised: March 2, 2016

A

DOI: 10.1021/acs.macromol.6b00004 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules Chart 1. Chemical Structures of IID, BDOPV, INDF, NBDOPV, and DIID

Scheme 1. Synthetic Route to DIID Derivatives and Polymersa

Reagents and conditions: (i) NEt3, dodecanoyl chloride, DCM, 0 °C to rt, 24 h; (ii) LiAlH4, THF, reflux, 80 h; (iii) NEt3, chloroacetyl chloride, DCM, 0 °C to rt, 24 h; (iv) NEt3, Pd(OAc)2, JohnPhos, toluene, 88 °C, 18 h; (v) AcOH, TsOH, P2O5, 125 °C, 24 h; (vi) Pd2(dba)3, P(o-tol)3, toluene, 110 °C, 48 h. a

compared to IID, and their D−A conjugated polymers showed either ambipolar or n-type transport properties.30−34 In the current paper, we synthesized a new IID derivative, i.e. DIID (Chart 1), in which two IID units are annulated. Compared to INDF, DIID has two additional N atoms for introducing more alkyls. Meanwhile, it has one more phenyl ring than NBDOPV. Four D−A conjugated polymers were synthesized with thiophene, bithiophene or (E)-1,2-bis(thiophen-2-yl)ethene as D-unit, and their photophysical, electrochemical, and semiconducting properties were evaluated in detail.

yielded 3 in a two-step yield of 80%. The intermediate 2 is almost insoluble in any commonly used solvents due to the presence of hydrogen bonds between molecules and was directly used for the next step. Compound 3 reacted with chloroacetyl chloride to afford compound 4 as a 1:1 mixture of rotamers.35 To obtain 5, Friedel−Crafts alkylation was first tested but unfortunately failed. Finally, the compound was successfully synthesized in a yield of 44% via C−H direct functionalization using the method developed by Buchwald and co-workers.35 Then DIID-1, DIID-2, and DIID-3 were prepared in yields of 39−46% by the condensation of 5 with 2 equiv of indoline-2,3-dione derivatives 6. Very recently, DIID derivatives were synthesized by Kelly et al. via a different approach. They first synthesized key intermediate bisisatin via Martinet isatin synthesis method,36 which then reacted with indoline-2-one derivatives to afford the targeted compounds.

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RESULTS AND DISCUSSION Synthesis. The synthesis of DIID derivatives and the polymers P1−P4 is outlined in Scheme 1. Reaction of commercially available naphthalene-1,5-diamine (1) and dodecanoyl chloride followed by the reduction with LiAlH4 B

DOI: 10.1021/acs.macromol.6b00004 Macromolecules XXXX, XXX, XXX−XXX

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Figure 1. Chemical structures (a), solution UV−vis−NIR absorption spectra (b), cyclic voltammograms (CV) curves (c), and HOMO/LUMO energy levels (d) of IID and DIID derivatives. The absorption spectra were measured in toluene with a concentration of 10−5 mol/L. Solution CV measurements were conducted in anhydrous dichloromethane at a scan rate of 40 mV/s with Bu4NPF6 (0.1 mol/L) as electrolyte, and energy levels were calculated from the redox onset potentials versus Fc/Fc+ (EHOMO = −4.8 eV).

DIID-based polymers P1−P4 were synthesized by typical Stille polycondensation with Pd2(dba)3/P(o-tol)3 as catalyst. The polymers P1, P2, and P3 have different D-units. For P3 and P4, alkyl chains with different branching position were used. This design allows us to study the effect of the structures of D-unit and alkyl chains on the properties of DIID-based D− A conjugated polymers. Previous studies have showed that both structural parameters noticeably influenced the properties of NBDOPV-based D−A conjugated polymers.32,33 All the polymers were purified by precipitation and Soxhlet extraction. The polymer P1 is readily soluble in chlorinated solvents such as chlorobenzene and o-dichlorobenzene (o-DCB) at room temperature, while P2, P3, and P4 are soluble in hot o-DCB. Number-average molecular weights (Mn) of the polymers are in the range of 35.5−82.1 kDa against polystyrene, as measured by high temperature gel permeation chromatography (GPC). Compared with P1 and P2, P3 and P4 have lower Mn and larger molar mass dispersity index (Đ), probably ascribed to their relatively poorer solubility and stronger aggregation capability in solution. All polymers show high thermal stability with 5% weight-loss temperature above 380 °C (Figure S15), and no phase transition was observed at 25−300 °C (Figure S16). Photophysical and Electrochemical Properties. First, photophysical and electrochemical properties of IID and DIID derivatives were studied in parallel to elaborate the effect of conjugation extension. As shown in Figure 1 and Table 1, DIID derivatives show noticeably red-shifted spectra and higher molar extinction coefficients (ε) compared to IID counterparts. The low-energy absorption maximum is red-shifted from 498/ 504 nm of IID-1/IID-2 to 697/714 nm of DIID-1/DIID-2. The molar extinction coefficients of DIID-1 and DIID-2 are about 2.4 and 3 times of those of IID-1 and IID-2, respectively. Extending the conjugation results in the elevated highest occupied molecular orbital (HOMO) energy levels and

Table 1. Photophysical and Electrochemical Properties of IID and DIID Derivatives compound IID-1 IID-2 DIID-1 DIID-2 a

λsol max/ε [nm]/ [×103 M−1 cm−1]a

EHOMO [eV]

ELUMO [eV]

Eopt g [eV]

370/10.1, 393/10.0, 498/2.9 385/16.0, 403/15.7, 504/5.8 350/26.4, 456/25.7, 697/8.8 350/35.8, 461/35.4, 714/13.9

−5.80

−3.49

2.06

−5.94

−3.67

2.03

−5.37

−3.79

1.46

−5.40

−3.88

1.43

In toluene. bEopt g = 1240/λonset.

decreased LUMO energy levels. For example, HOMO energy level increases from −5.80 eV of IID-1 to −5.37 eV of DIID-1 while LUMO energy level decreases from −3.49 to −3.79 eV, leading to significantly reduced optical bandgap (Eopt g : 2.06 versus 1.46 eV). This result is well consistent with density functional theory (DFT) calculations (Figure S17). Both HOMO and LUMO of DIID-1 are delocalized over the whole molecules. The introduction of Br atoms causes an ∼0.1 eV reduction of both HOMO and LUMO. All these results imply that DIID is a promising building block for low bandgap and ambipolar/n-type conjugated polymers. Figure 2 shows solution and film UV−vis−NIR absorption spectra of polymers P1−P4 and the frontier orbital distribution of their trimers, and the related data are summarized in Table 2. Two absorption bands are observed for all four polymers, which are in the ranges of 400−520 and 520−950 nm, respectively, corresponding to π−π* transition and the internal charge transfer (ICT) transition between D- and A-units. The polymers show very similar absorption spectra in both solution and film states with the difference of the low-energy absorption maxima less than 10 nm (for example, 784−788 nm in solution and 781−787 nm in films). Eopt g values of the four polymers are C

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Figure 2. Solution (a) and film (b) UV−vis−NIR absorption spectra of the polymers and the frontier orbital distribution of their trimers based on optimized backbones (c). Solution spectra were measured in o-DCB with a concentration of 10−5 mol/L of repeating units. Films were prepared by spin-casting the o-DCB solutions with a concentration of 5.0, 3.0, 3.0, and 2.0 mg/mL for P1−P4 on quartz substrates. In DFT calculations, alkyls were replaced by methyl groups for simplifying the calculation.

Table 2. Molecular Weights and Photophysical and Electrochemical Properties of P1, P2, P3, and P4 absorption properties polymer

Mn (kDa)/Đ

P1 P2 P3 P4

52.4/1.63 82.1/2.07 46.2/5.31 35.5/7.18

λsmax (nm)a 483, 469, 468, 472,

667, 695, 708, 715,

787 787 788 784

electrochemical properties

λfmax (nm)a 480, 468, 467, 473,

660, 689, 681, 681,

786 787 781 781

b Eopt g (eV)

EHOMO (eV)c

ELUMO (eV)c

Egcv (eV)d

1.29 1.31 1.29 1.30

−5.16 −5.16 −5.24 −5.38

−3.66 −3.58 −3.58 −3.71

1.50 1.58 1.67 1.69

The superscripts “s” and “f” refer to “solution” and “film”, respectively. bThe optical bandgap (Eopt g ) was calculated from film absorption onset. HOMO and LUMO energy levels were estimated from redox onset potentials versus Fc/Fc+ (EHOMO = −4.8 eV). dEcv g = ELUMO − EHOMO.

a c

almost the same (∼1.30 eV, see Table 2). From solution to film state, the spectra are almost same for P1 and P2 while those of P3 and P4 have a small blue-shift. This implies that the polymer chains already aggregate in solution. The phenomena of P3 and P4 are very similar to that of NBDOPV-based polymers reported recently,32 indicating that P3 and P4 may adopt H-type aggregation in film state. It should be noted that P2 has an obvious shoulder peak at 862 nm compared with other three polymers. This phenomenon may be ascribed to its much higher molecular weight, which endows polymer chains enhanced aggregation ability.37 Optimized conformations of the four polymers are depicted in Figure 2c. Compared with P2, P3, and P4, P1 shows relatively larger curvature, which may influence its capability to form ordered packing in solid state. Both HOMO and LUMO of the trimers mainly localize on DIID core for all four polymers, consistent with the similar UV−vis−NIR spectra of the polymers as aforementioned. Depicted in Figure 3 is the thin film cyclic voltammograms (CV) of the polymers. All four polymers show quasi-reversible p- and n-doping processes. HOMO/LUMO energy levels of the polymers were estimated from the redox onset potentials versus Fc/Fc+ (EHOMO = −4.8 eV), which are −5.16/−3.66 eV for P1, −5.16/−3.58 eV for P2, −5.25/−3.58 eV for P3, and −5.38/−3.71 eV for P4. Increasing the conjugation length of D-units does not cause the elevation of HOMO energy levels. Compared with P1 and P2, P3 even has deeper HOMO energy level. This phenomenon is unusual for D−A conjugated polymers. In general, the HOMO of D−A conjugated polymer

Figure 3. Film cyclic voltammograms (CV) of the polymers. The measurements were conducted in anhydrous acetonitrile with Bu4NPF6 (0.1 mol/L) as electrolyte. The films were prepared by spin-casting o-DCB solutions with a concentration of 5.0, 3.0, 3.0, and 2.0 mg/mL for P1−P4 on glassy carbon electrode.

is mainly determined by its D-unit.38 Since the DFT calculated HOMO energy levels of thiophene, bithiophene, and 1,2bis(thiophen-2-yl)ethane are −6.3, −5.5, and −5.2 eV, respectively, it was expected that the HOMO energy levels of the polymers should be in the order of P1 < P2 < P3. We attribute this unusual phenomenon to the fact that the HOMOs of the polymers are mostly localized on the DIID cores, as shown in Figure 2c. P4 shows a lower HOMO energy level than P3, which may be attributed to their different packing behavior in solid state. It is known that the branching position of the alkyl substituents has strong influence on the π−π D

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Macromolecules Table 3. OTFT Device Performance of Polymers P1−P4 p-channel polym.

device structure

P1

BGTC

P2

TGBC BGTC

P3

TGBC BGTC

P4

TGBC BGTC TGBC

a

Taa (°C) as cast 250 200 as cast 200 200 as cast 200 200 as cast 200 290

μmaxb (cm2/V s) −4

9.6 × 10 3.2 × 10−3 1.1 × 10−3 0.56 1.55 0.41 0.67 1.79 0.45 0.20 0.75 0.32

n-channel

μaveb (cm2/V s) −4

7.1 × 10 3.0 × 10−3 9.4 × 10−4 0.48 1.29 0.34 0.49 1.47 0.36 0.15 0.62 0.27

VTc (V)

Ion/Ioffd

μmaxb (cm2/V·s)

μaveb (cm2/V s)

VTc (V)

Ion/Ioffd

5 to 10 0 to 4 −5 to −17 2 to 10 2 to 8 −13 to −20 −13 to 0 −6 to 12 −13 to −16 −10 to −3 −5 to 2 −30 to −40

10 −10 103−104 P2 ≈ P4 > P1. Note that P3 and P2 exhibit comparable device performance although the former polymer affords the film with higher packing order. This can be attributed to the higher molecular weight of P2 (Mn = 82.1 and F

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Figure 6. AFM height images of as-cast (a−d) and thermally annealed (e−h) films of P1 (a, e), P2 (b, f), P3 (c, g), and P4 (d, h). Thermal annealing of the films was conducted at 200 °C for 10 min. dissolved in 300 mL of CHCl3. Insoluble residues were removed by filtration, and the resulting solution was dried with MgSO4. The product was obtained as a pale white solid (3.03 g, 80% yield in two steps) after the solvent had been removed. 1H NMR (CDCl3, 400 MHz, ppm): δ 7.32−7.28 (t, J = 8.0 Hz, 2H), 7.15−7.13 (d, J = 8.4 Hz, 2H), 6.61−6.59 (d, J = 7.6 Hz, 2H), 4.32−4.29 (t, J = 5.0 Hz, 2H), 3.27−3.23 (q, J = 7.2 Hz, 4H), 1.78−1.73 (m, J = 7.6 Hz, 4H), 1.37− 1.27 (m, 36H), 0.91−0.87 (t, J = 6.4 Hz, 6H). N,N′-(1,5-Naphthalene)bis(N-dodecyl-2-chloroacetamide) (4). To a suspension of 3 (0.50 g, 1.01 mmol) in CH2Cl2 (25 mL) was added chloroacetyl chloride (1.80 mL, 2.22 mmol) dropwise at 0 °C. The resulting mixture was warmed to room temperature and stirred until becoming clear. Then NEt3 (0.34 mL, 2.43 mmol) was added, and the mixture was stirred for another 16 h before H2O (20.0 mL) was added. The mixture was extracted with CH2Cl2. Organic extracts were washed with brine twice and then dried with MgSO4 before filtered and concentrated in a vacuum. The crude product was purified by column chromatography on silica gel using petroleum ether (PE):ethyl acetate (EA) (5:1, v/v) as eluent to afford 4 as a pale yellow solid (0.51 g, 78%). 1H NMR (CDCl3, 400 MHz, ppm): δ 7.91−7.89 (d, J = 8.4 Hz, 2H), 7.66−7.62 (t, J = 7.6 Hz, 2H), 7.51− 7.49 (d, J = 7.2 Hz, 2H), 4.33−4.27 (m, 2H), 3.77−3.72 (m, 2H), 3.68−3.63 (m, 2H), 3.28−3.25 (m, 2H), 1.67−1.23 (m, 40H), 0.88− 0.85 (t, J = 6.8 Hz, 6H). 13C NMR (CDCl3, 100 MHz, ppm): δ 166.6, 138.3, 132.0, 128.1, 127.7, 127.6, 123.9, 123.8, 50.3, 42.2, 42.1, 32.0, 29.7, 29.4, 28.1, 26.9, 22.8, 14.2. 1,6-Didodecyl-6,8-dihydroindolo[7,6-g]indole-2,7(3H,8H)dione (5). To a Schlenk tube were added compound 4 (0.500 g, 0.772 mmol), palladium(II) acetate (Pd(OAc)2, 20.8 mg, 92.6 μmol, 12.0 mol %), and 2-(di-tert-butylphosphino)biphenyl (JohnPhos, 55.0 mg, 0.185 mmol, 24.0 mol %). The tube was evacuated and backfilled with argon three times. Anhydrous toluene (8.00 mL) and dry NEt3 (0.32 mL) were added before the reaction mixture was allowed to warm to 88 °C for 18 h. Then the reaction mixture was cooled to room temperature and concentrated in a vacuum. The dark solid was purified by chromatography on silica gel using PE:EA (6:1, v/v) as eluent to give the product as a pale yellow solid in a yield of 44% (198 mg). 1H NMR (CDCl3, 400 MHz, ppm): δ 7.93−7. 91 (d, J = 8.8 Hz, 2H), 7.41−7.39 (d, J = 8.8 Hz, 2H), 4.26−4.22 (t, J = 7.6 Hz, 4H), 3.66 (s, 4H), 1.83−1.78 (m, 4H), 1.29−1.25 (m, 36H), 0.89−0.86 (t, J = 6.8 Hz, 6H). 13C NMR (CDCl3, 100 MHz, ppm): δ 176.6, 140.8, 122.1, 121.9, 120.4, 115.8, 43.0, 36.2, 32.0, 29.8, 29.5, 29.4, 26.9, 22.8, 14.2. MALDI-TOF MS: calcd for C38H58N2O2: 574.45. Found: 574.4. Anal. Calcd for C38H58N2O2 (%): C, 79.39; H, 10.17; N, 4.87. Found: C, 78.03; H, 10.063; N, 4.69. [3E,8E]-3,8-Bis(1-(2-decyltetradecyl)-2-oxoindolin-3-ylidene)-1,6-didodecyl-6,8-dihydroindolo[7,6-g]indole-2,7(1H,3H)-dione (DIID-1). In a round-bottom flask was added 6a (148

46.2 kDa for P2 and P3, respectively). It is known that high molecular weight is beneficial for the charge transport in solid state.46,47 Figure 6 shows film AFM height images of the polymers before and after annealing at 200 °C for 10 min. All the films were continuous and characterized by fiber-like morphology, which establish interconnected polymer chain networks and form highly efficient pathways for charge carrier transport. After thermal annealing, domain sizes became larger, which is consistent with the slightly enhanced OTFT mobility.

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CONCLUSIONS In conclusion, we have developed a new approach to synthesize DIID, which comprises two annulated IID units. Compared with IID, DIID has lower bandgap owing to decreased LUMO and enhanced HOMO. Four D−A conjugated polymers based on this new electron-deficient aromatic unit were synthesized. They all show very broad absorption with the spectra covering 400−950 nm. All polymers exhibit ambipolar transport character with the device performance depending on OTFT geometry. P3, which is consisted of alternatively bonded DIID and (E)-1,2-bis(thiophen-2-yl)ethene units, shows the best device performance. Hole and electron mobilities of 1.79 and 0.087 cm2/(V s), respectively, have been demonstrated with BGTC OTFTs. Its TGBC OTFTs exhibits more balanced transport properties with maximum hole and electron mobilities of 0.45 and 0.26 cm2/(V s), respectively. Our study implies that DIID is a promising building block for high mobility low bandgap conjugated polymers.

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EXPERIMENTAL SECTION

N,N′-(1,5-Naphthalene)didodecanamide (2). To a suspension of naphthalene-1,5-diamine (1, 1.00 g, 6.32 mmol) and triethylamine (NEt3, 2.10 mL) in CH2Cl2 (100 mL) was added dodecanoyl chloride (3.30 mL, 13.9 mmol) dropwise at 0 °C. The reaction mixture was warmed to room temperature and stirred for 24 h. The solid was collected by filtration, thoroughly washed with water and ethanol, and then was dried in a vacuum. The obtained off-white solid was directly used in the next step. N,N′-Didodecylnaphthalene-1,5-diamine (3). To a suspension of 2 (4.00 g, 7.65 mmol) in THF (120 mL) was added LiAlH4 (1.19 g, 31.35 mmol) at 0 °C. The mixture was refluxed for 80 h, and then NaOH aqueous solution (100 mL, 0.375 mol/L) was added dropwise at 0 °C. The solid was collected and washed with DCM before G

DOI: 10.1021/acs.macromol.6b00004 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules mg, 0.300 mmol), 5 (80.0 mg, 0.140 mmol), P2O5 (15.4 mg, 0.10 mml), toluenesulfonic acid monohydrate (9.26 mg, 0.050 mmol), and acetic acid (8.00 mL). The mixture was evacuated and backfilled with argon twice and then stirred at 125 °C for 24 h. After the mixture was cooled to room temperature, water (20.0 mL) was added. The mixture was extracted with CHCl3. The organic extracts were washed with brine and dried with MgSO4. After the solvent had been removed, the residue was purified by column chromatography on silica gel using PE:DCM (4:1, v/v) to afford 6a as a dark solid in a yield of 39% (83 mg). 1H NMR (CDCl3, 400 MHz, ppm): δ 9.10−9.08 (d, J = 8.0 Hz, 2H), 9.01−8.99 (d, J = 9.2 Hz, 2H), 7.83−7.80 (t, J = 9.6 Hz, 2H), 7.37−7.34 (t, J = 7.6 Hz, 2H), 7.07−7.03 (t, J = 8.0 Hz, 2H), 6.79− 6.77 (d, J = 7.6 Hz, 2H), 4.28−4.26 (t, J = 7.6 Hz, 4H), 3.69−3.67 (d, J = 7.2 Hz, 4H), 1.87 (m, 6H), 1.35−1.23 (m, 116H), 0.88−0.85 (m, 18H). 13C NMR (CDCl3, 100 MHz, ppm): δ 169.7, 168.2, 145.5, 143.3, 133.9, 132.9, 132.5, 129.5, 124.8, 122.1, 120.1, 116.8, 108.5, 44.9, 43.7, 36.4, 32.1, 31.8, 30.2, 29.8, 29.6, 29.5, 27.1, 26.7, 14.3. MALDI-TOF MS: calcd for C102H160N4O4: 1505.24. Found: 1505.2. Anal. Calcd for C110H156N4O (%): C, 81.24; H, 10.64; N, 3.79. Found: C, 81.26; H, 10.677; N, 3.24. [3E,8E]-3,8-Bis(6-bromo-1-(2-decyltetradecyl)-2-oxoindolin3-ylidene)-1,6-didodecyl-6,8-dihydroindolo[7,6-g]indole-2,7(1H,3H)-dione (DIID-2). DIID-2 was synthesized in a same procedure from 5 and 6b. Yield: 41% (209 mg). 1H NMR (CDCl3, 400 MHz, ppm): δ 8.95−8.93 (d, J = 8.4 Hz, 2H), 8.88−8.86 (d, J = 10.0 Hz, 2H), 7.62−7.60 (d, J = 9.6 Hz, 2H), 7.11−7.08 (dd, J1 = 1.6 Hz, J2 = 8.4 Hz, 2H), 6.77−6.76 (d, J = 1.6 Hz, 2H), 4.20−4.17 (t, J = 7.6 Hz, 4H), 3.59−3.57 (d, J = 7.2 Hz, 4H), 1.84−1.80 (m, 6H), 1.46−1.23 (m, 116H), 0.88−0.86 (m, 18H). 13C NMR (CDCl3, 100 MHz, ppm): δ 169.5, 167.9, 146.2, 143.2, 132.4, 132.3, 130.7, 127.0, 124.8, 122.9, 120.8, 119.8, 116.7, 111.7, 44.9, 43.7, 36.3, 32.1, 31.7, 29.8, 29.6, 29.5, 27.1, 26.6, 26.8, 22.8, 14.2. MALDI-TOF MS: calcd for C102H158Br2N4O4: 1661.06. Found: 1661.1. Anal. Calcd for C102H158Br2N4O4 (%): C, 73.41; H, 9.49; N, 3.42. Found: C, 73.22; H, 9.466; N, 3.19. [3E,8E]-3,8-Bis(6-bromo-1-(4-decyltetradecyl)-2-oxoindolin3-ylidene)-1,6-didodecyl-6,8-dihydroindolo[7,6-g]indole-2,7(1H,3H)-dione(DIID-3). DIID-3 was synthesized in a same procedure from 5 and 6c. Yield: 46% (570 mg). 1H NMR (CDCl3, 400 MHz, ppm): δ 8.98−8.96 (d, J = 8.8 Hz, 2H), 8.94−8.92 (d, J = 9.2 Hz, 2H), 7.69−7.67 (d, J = 9.6 Hz, 2H), 7.14−7.11 (dd, J1 = 1.6 Hz, J2 = 8.8 Hz, 2H), 6.85 (d, 2H), 6.77−6.76 (d, J = 1.6 Hz, 2H), 4.23−4.19 (t, J = 7.6 Hz, 4H), 3.72−3.68 (t, J = 7.6 Hz, 4H), 1.84−1.80 (m, 4H), 1.66 (m, 4H), 1.34−1.24 (m, 114H), 0.88−0.85 (m, 18H). 13C NMR (CDCl3, 100 MHz, ppm): δ 169.5, 167.6, 145.8, 143.4, 132.5, 132.4, 130.9, 127.1, 124.9, 123.0, 120.9, 119.9, 116.7, 111.5, 43.7, 40.8, 37.4, 33.7, 32.1, 31.1, 29.9, 29.8, 29.5, 27.1, 26.8, 24.7, 22.8, 14.3. MALDI-TOF MS: calcd for C102H158Br2N4O4: 1661.06. Found: 1661.1. Anal. Calcd for C102H158Br2N4O4 (%): C, 73.41; H, 9.49; N, 3.42. Found: C, 73.4; H, 9.591; N, 3.21. P1. In a Schlenk tube was charged with DIID-3 (300 mg, 0.180 mmol), 2,5-bis(trimethylstannyl)thiophene (74.6 mg, 0.180 mmol), tris(dibenzylideneacetone)dipalladium (Pd2(dba)3, 3.3 mg, 4 × 10−3 mmol), tri-o-tolylphosphine (P(o-tol)3, 8.8 mg, 2.9 × 10−2 mmol), and toluene (29.0 mL). The mixture was evacuated and backfilled with argon three times and stirred at 120 °C for 48 h. Then 0.50 mL of bromobenzene was added, and the reaction was continued for another 12 h. After being cooled to room temperature, the mixture was added dropwise into 250 mL of methanol. The precipitates were collected by filtration and then redissolved in o-DCB (30 mL) at 100 °C. Aqueous solution of sodium diethyldithiocarbamate trihydrate (80 mL, 2.5 mg/ mL) was added, and then the mixture was stirred overnight to remove the catalyst residues. The organic phase was separated from mixture and added dropwise into 250 mL of ethanol. The solid was collected by filtration for extraction with acetone and hexane on a Soxhlet’s extractor, and the residue was dried and dissolved in o-DCB. P1 was obtained as a black solid in a yield of 74% (213 mg) by precipitating the o-DCB solution of the polymer in methanol, filtrated, and then dried in a vacuum. The relatively low yield of the polymer was attributed to the loss in the process of removing the catalyst residues.

Emulsification appeared in this process, and the emulsion layer was discarded. Anal. Calcd for (C106H162N4O4S)n (%): C, 80.15; H, 10.28; N, 3.53; S, 2.02. Found: C, 78.83; H, 10.39; N, 3.36; S, 2.10. P2. P2 was synthesized form 5,5′-bis(trimethylstannyl)-2,2′bithiophene and DIID-3 following the procedure for the synthesis of P1. Yield: 76% (229 mg). Anal. Calcd for (C110H164N4O4S2)n (%): C, 79.08; H, 9.89; N, 3.55; S, 3.84. Found: C, 78.02; H, 10.30; N, 3.17; S, 3.57. P3. P3 was synthesized form 1,2-bis(5-(trimethylstannyl)thiophen2-yl)ethene and DIID-3 following the procedure for the synthesis of P1.Yield: 87% (265 mg). Anal. Calcd for (C112H166N4O4S2)n (%): C, 79.28; H, 9.86; N, 3.30; S, 3.78. Found: C, 78.53; H, 9.95; N, 3.16; S, 3.77. P4. P4 was synthesized form 1,2-bis(5-(trimethylstannyl)thiophen2-yl)ethene and DIID-2 following the procedure for the synthesis of P1.Yield: 83% (254 mg). Anal. Calcd for (C112H166N4O4S2)n (%): C, 79.28; H, 9.86; N, 3.30; S, 3.78. Found: C, 78.20; H, 9.87; N, 3.16; S, 3.79.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.6b00004. Instruments, experimental details for preparation and characterization of OTFT devices, NMR spectra of intermediates and monomers, TGA and DSC traces of the polymers, and other device data (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail [email protected] (Y.H.G.). *E-mail [email protected] (H.K.T.). *E-mail [email protected] (J.Q.D.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is supported by National Basic Research Program of China (973 Project, No. 2014CB643504) of Chinese Ministry of Science and Technology, the National Natural Science Foundation of China (No. 51333006), and the Strategic Priority Research Program of the Chinese Academy of Sciences (No. XDB12010300).

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REFERENCES

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