Fluorodiphenylethene-Containing Donor–Acceptor Conjugated

Mar 30, 2016 - Design and effective synthesis methods for high-performance polymer semiconductors in organic field-effect transistors. Longxian Shi , ...
1 downloads 3 Views 5MB Size
Download PDF
Article pubs.acs.org/Macromolecules

Fluorodiphenylethene-Containing Donor−Acceptor Conjugated Copolymers with Noncovalent Conformational Locks for Efficient Polymer Field-Effect Transistors Weifeng Zhang, Keli Shi, Jianyao Huang, Dong Gao, Zupan Mao, Dizao Li, and Gui Yu* Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China S Supporting Information *

ABSTRACT: The diphenylethene moiety is a versatile building block that offers several chemically functionalizable sites, allowing easy modulation of electronic properties of the resulting polymers and providing numerous opportunities for discovering related structure−property relationships. In this study, we report a series of difluorodiphenylethene-based copolymers with noncovalent conformational locks for applications in polymer field-effect transistors. Different fluorination positions lead to different type of intra- and intermolecular interactions, backbone conformations, and eventually different device performances. 2,2′-Difluorodiphenylethene-based copolymers P2DFPE-n containing F···H−C conformation locks exhibit obviously enhanced hole mobilities of 1.3−1.5 cm2 V−1 s−1, whereas 3,3′-difluorodiphenylethenebased copolymers P3DFPE-n containing F···H−C and F···S conformation locks show lower mobilities of 0.2−0.4 cm2 V−1 s−1. AFM and 2D-GRXD investigations indicate that P2DFPE-n takes predominantly edge-on orientation packing mode, forming crystalline and highly ordered thin films with small π−π stacking distances of 3.59−3.68 Å. However, P3DFPE-n adopts random close molecular packing mode in solid states.

■

INTRODUCTION Solution-processable conjugated polymers have attracted considerable attention from both academic and industrial fields because of their potential to fabricate various electronic devices such as radio-frequency identification, flexible and large area displays, and sensors, based on polymer field-effect transistors (PFETs) via cost-effective graphic printing processes.1−4 Up to the present time, however, realizing highly efficient PFETs is still be challenged by the poor interchain packing of the polymers and macroscopic defects originating from the weak van der Waals forces among the adjacent polymers.5 Therefore, the exploration of structure−property relationships of polymer semiconductors in order to form highly ordered, crystalline, and tight packing thin films, and high charge carrier transport properties are of prime importance to researchers. Over the past decades, a wide variety of donor−acceptor (D−A) copolymers had been designed, synthesized, and applied in PFET devices.6−11 Several copolymers exhibited impressively record high p-type, n-type, or ambipolar charge transport characteristics.12−16 Meanwhile, some important design principles had been set up or put forward, such as planarity of conjugated backbones,17 frontier energy levels,18,19 side chains,20 molecular symmetry,21 and molecular size/ weight, etc.22 In recent years, purposeful introduction of heteroatomic substituents has been regarded as an effective approach in improving charge carrier transport properties of polymer semiconductors.23−25 The heteroatomic substituents © XXXX American Chemical Society

could induce the emergence of intramolecular noncovalent interactions, which act as “conformational locks” giving rise to locked backbone conformations. Additionally, intermolecular interactions and frontier energy levels could also be tuned by the introduction of substituent groups along with the formation of highly planar conjugated backbones. Since the concept was put forward, several copolymers with conformational locks have been developed. For example, the enhanced mobility of benzotriazole-based polymer was attributed to the decreased torsional angle (∼0°) due to intramolecular C−F···S interactions and the small van der Waals radius of the F atom.26 Fluorinated benzodifurandione-based copolymers with F···H−C noncovalent interactions showed that the locating position of conformational locks affect greatly charge carrier transport.27 Besides, the solution processability of semiconducting polymers could be improved when suitable conformational locks were incorporated.28 Generally speaking, the introduction of intramolecular noncovalent interactions and conformational locks on conjugated backbones has great potentials in improving electronic properties of polymer semiconductors and warrant further investigations. Until now, the D−A copolymers with high mobility are always constructed based on several classical electron-withReceived: January 21, 2016 Revised: March 26, 2016

A

DOI: 10.1021/acs.macromol.6b00144 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules

Scheme 1. Chemical Structures of 2DFPE and 3DFPE and Schematic Noncovalent Intramolecular Interactions in P2DFPE-n and P3DFPE-n (in Dimer)

Scheme 2. Synthetic Routes of P2DFPE-n and P3DFPE-n (n = 1, 2, and 3)

carrier transport properties. P2DFPE-n exhibits higher hole mobilities of 1.3−1.5 cm2 V−1 s−1, whereas P3DFPE-n affords low mobilities of 0.2−0.4 cm2 V−1 s−1 in solution-processed PFETs. The thin film microstructures analyses suggest that P2DFPE-n take predominantly edge-on orientation packing mode on OTS-modified SiO2 substrates, forming crystalline and highly ordered thin films with small π−π stacking distances of 3.59−3.68 Å. However, P3DFPE-n adopts random close molecular packing mode in solid states. These results highlight that different fluorination positions can induce different noncovalent interactions and backbone conformations, which have important influences on electronic properties of semiconducting polymers.

drawing or electron-donating building blocks such as diketopyrrolopyrrole (DPP), isoindigo, benzodifurandione, thieno[3,2-b]thiophene, and (E)-diarylethenes (DAEs).13−16 Diphenylethene is one kind of DAEs and could offer several functionalizable sites, allowing easy introduction of noncovalent conformational locks on π-conjugated backbones. The capacity is of great importance for discovering structure−property relationships of polymeric semiconductors. In this work, we report a series of difluorodiphenylethene-based copolymers with noncovalent conformational locks, namely P2DFPE-n and P3DFPE-n (n = 1, 2, and 3). P2DFPE-n was synthesized based on 2,2′-difluorodiphenylethene (2DFPE) building blocks with F···H−C hydrogen bonds, while P3DFPE-n was constructed based on 3,3′-difluorodiphenylethene (3DFPE) building blocks, which induce the emergence of F···H−C and F···S conformation locks (Scheme 1). P2DFPE-n and P3DFPE-n show different backbone conformations with intra- and intermolecular interactions and thus afford various charge

■

RESULTS AND DISCUSSION Synthesis and Thermal Stability. The synthetic routes of 2DFPE- and 3DFPE-based monomers 3 and 6 are outlined in

B

DOI: 10.1021/acs.macromol.6b00144 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules Table 1. Optical and Electrochemical Properties of P2DFPE-n and P3DFPE-n copolymer P2DFPE-1 P2DFPE-2 P2DFPE-3 P3DFPE-1 P3DFPE-2 P3DFPE-3

Mna (kDa) 35.3 80.2 34.5 23.9 17.2 20.8

PDIa 1.78 2.46 3.08 3.14 2.09 2.18

λmax (nm)

Tdb (°C) 400 381 396 372 384 395

646, 652, 650, 652, 646, 642,

c

702 /644, 716c/646, 714c/644, 714c/646, 708c/646, 704c/640,

d

708 712d 710d 716d 708d 706d

e Eopt (eV) g

f EOx onset (V)

f Ered onset (V)

HOMOf (eV)

LUMOg (eV)

1.43 1.43 1.42 1.40 1.40 1.40

1.02 1.00 0.98 0.94 0.92 0.92

−0.80 −0.81 −0.81 −0.80 −0.80 −0.82

−5.42 −5.40 −5.38 −5.34 −5.32 −5.32

−3.60 −3.59 −3.59 −3.60 −3.60 −3.58

Molecular weights determined by GPC at 150 °C. bOnset decomposition temperature (5% weight loss) measured by TGA. cIn chlorobenzene g solutions. dThin films. eCalculated from thin film absorption cutoff values. fDetermined by CV. HOMO = −(4.4 + EOx Onset) eV. LUMO = −(4.4 + red Eonset) eV. a

Figure 1. (a, b) Top and (c) side views. (d) Packing diagram and intermolecular F···H−C interactions of single-crystal X-ray structure of 2DFPEbased intermediate 2 with 50% probability ellipsoids (hydrogen atoms are omitted for clarity).

2DFPE (2DFPE-T) and thiophene-flanked 3DFPE (3DFPET) using density functional theory at the B3LYP/6-31G* level (Figures 1 and 2). The single crystal of intermediate 2 was

Scheme 2. The reductive coupling reaction of 4-bromo-2fluorobenzaldehyde (1) or 4-bromo-3-fluorobenzaldehyde (3) under McMurry conditions gave the key intermediates 2 or 5 in high yields.29,30 In the presence of PdCl2(dppf), intermediates 2 and 5 reacted with bis(pinacolato)diboron affording the desired monomers 3 and 6 in moderate yields, respectively.31 Suzuki copolymerization of DPP-based monomer 7, 8, or 9 with monomer 3 or 6 supplied the crude polymer materials. After carefully purified by Soxhlet extraction for the removal of low-molecular-weight and catalytic impurities, the title polymers P2DFPE-n and P3DFPE-n (n = 1, 2, and 3) were obtained in excellent yields. These copolymers were soluble in hot chlorinated solvents such as chlorobenzene and ochlorobenzene, etc. These copolymers were characterized by high temperature 1H NMR (100 °C) and gel permeation chromatography (GPC) with PS polystyrene as standard and 1,2,4-trichlorobenzene as eluent. Their number-average molecular weights (Mn) and the corresponding polydispersity indexes (PDIs) were in a range of 17.2−80.2 kDa and 1.78−3.14 for P2DFPE-n and P3DFPE-n (n = 1, 2, and 3) (Table 1), respectively. Their thermal behaviors were also investigated by means of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The decomposition temperature (Tdec) with 5% weight loss of the three polymers occurs at around 380 °C for 2DFPE- and 3DFPE-based copolymers (Figures S1 and S2). The results manifest that these polymers have good thermal stability. No glass transition was observed from the DSC characterization, during the scan from 30 to 300 °C at a rate of 10 °C/min under nitrogen. Noncovalent Conformational Locks in 2DFPE- and 3DFPE-Based Moieties. In order to deeply understand the noncovalent intramolecular interactions in 2DFPE- and 3DFPE-based moieties, we grew the single crystal of intermediate 2 (X-ray crystallographic data, see Table S1) and optimized the molecular structures of thiophene-flanked

Figure 2. Optimized molecular structures of (a, b) 2DFPE-T and (c, d) 3DFPE-T and dihedral angles (α, β) in 2DFPE-T and (γ, θ) in 3DFPE-T.

prepared by slow evaporation of solvent from a dilute ethyl acetate solution. The crystalline structure of intermediate 2 is triclinic and has two conformers, namely conformation-1 and conformation-2. The conformation-1 owns six-membered-ring intramolecular hydrogen bonds (F···H−C of 2.20 Å, the sum of van der Waals radii is 2.67 Å),32 while the conformation-2 owns five-membered-ring intramolecular hydrogen bonds (F···H−C of 2.42 Å) (Figure 1a−c). Moreover, intermolecular F···H−C C

DOI: 10.1021/acs.macromol.6b00144 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules

Figure 3. UV−vis−NIR absorption spectra of P2DFPE-n and P3DFPE-n in (a) chlorobenzene solutions and (b) thin films. CV traces of (c) P2DFPE-n and (d) P3DFPE-n.

have similar absorption behavior in solution and thin film due to the homologous conjugated backbones. Nonetheless, the absorption profile of P3DFPE-n is broader than that of P2DFPE-n due to the more planar conjugated backbone of P3DFPE-n. In chlorobenzene solutions, the absorption profiles of P2DFPE-n and P3DFPE-n both own the high-energy bands, ranging from 350 to 500 nm with the maximum peaks of ca. 420 nm, and can be assigned to the π−π* transition. P2DFPE-n and P3DFPE-n also exhibit broad low-energy absorption bands ranging from 500 to ca. 800 nm with the maximum peaks of around 710 nm, originating from the intramolecular charge transfer (ICT) between the DPP and 2DFPE or 3DFPE units.33,34 In addition, temperature-dependent UV−vis absorption spectra of P2DFPE-n were recorded in dilute dichlorobenzene solutions (Figure S3). Their absorption profiles upon heating (40, 60, 80, 100, and 120 °C) are slightly different than those of the polymers at room temperature. The comparison results mean that strongly intermolecular interactions of polymer chains occur in dilute solutions and force the polymers to be in their respective aggregated state even at high temperature.35 Compared with in solutions, the P2DFPE-n and P3DFPE-n thin films exhibit almost the same ICT peaks and differential vibrational absorption shoulder peaks; the former is attributed to the similar conjugated backbones in solid state, and the latter may be ascribed to the different aggregation or π−π stacking behaviors between P2DFPE-n and P3DFPE-n thin films. On the basis of the absorption edges, the optical bandgap (Eopt g ) of P2DFPE-n and P3DFPE-n was estimated to be ca.1.43 and 1.40 eV, respectively. Electrochemical properties of P2DFPE-n and P3DFPE-n were explored by cyclic voltammetry (CV) measurement (Figures 3c and 3d). The copolymers all show quasi-reversible oxidation and reduction

interactions could be observed in the single crystal (Figure 1d). The ratio of conformation-1 and conformation-2 is 1:2. The presence of these intramolecular hydrogen bonds and conformational locks is beneficial to keeping planar backbone conformation. Theoretical simulation results indicate that 3DFPE-T owns more planar conjugated backbone than 2DFPE-T. As shown in Figure 2, the dihedral angles (γ, 10.95°, or γ, 17.46°) in 3DFPET are clearly smaller than that (α, β 24.24°) in 2DFPE-T. The results imply that the introduction of fluorine atoms on the 3,3′-position of the DPE moiety could induce stronger intramolecular F···H−C (conformation d) or F···S interactions (conformation c), which more effectively promote the conjugated backbone planarity of 3DFPE-T. It is notable that the conformation d has slightly lower energy than conformation c. The energy difference is about 1.3 kJ/mol, and the conformation d is dominant. By contrast, the two conformation isomers with six-membered-ring (conformation a) or fivemembered-ring F···H−C hydrogen bonds (conformation b) are almost isoenergetic and thus coexist in equal quantity. Meanwhile, we speculate that multiple intermolecular interactions including F···H−C and F···S originating from fluorination also occur in the P3DFPE thin films. The above experimental and theoretical modeling results indicate that the introduction of fluorine atoms endows 2DFPE- and 3DFPEbased copolymers with strongly intra- and intermolecular interactions. Optical and Electrochemical Properties of P2DFPE-n and P3DFPE-n. The absorption spectra of P2DFPE-n and P3DFPE-n in chlorobenzene solutions and thin films are shown in Figures 3a and 3b, and the corresponding photophysical data are listed in Table 1. As expected, P2DFPE-n and P3DFPE-n D

DOI: 10.1021/acs.macromol.6b00144 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules

Figure 4. Typical transfer and output characteristics of PFETs based on P2DFPE-1 and P3DFPE-2: (a, c) for P2DFPE-1 and (b, d) for P3DFPE-2.

Table 2. Summary of P2DFPE-n- and P3DFPE-n-Based PFET Device Performances copolymers P2DFPE-1 P2DFPE-2 P2DFPE-3 P3DFPE-1 P3DFPE-2 P3DFPE-3

tempa [°C] 180 180 180 180 160 180

μmax (μavg)b,c [cm2 V−1 s−1] 1.36 1.48 1.41 0.23 0.35 0.34

Ion/Ioffb

Vthb [V]

π−πd [Å]

d−dd [Å]

10 −10 106−107 106−107 106−107 106−107 106−107

0 −2.28 −1.49 −1.49 3.56 −2.74

3.68 3.59 3.59 3.61 3.62 3.48

20.67 21.73 22.34 19.96 23.37 23.07

6

(0.99) (1.18) (0.78) (0.18) (0.18) (0.28)

7

Optimal annealing temperatures. bμavg was summarized from over 10 devices for each copolymers. cPFFTs had a channel width (W) of 1400 μm and a channel length (L) of 50 for P2DFPE-n and P3DFPE-3 or 20 μm for P3DFPE-1 and -2. dThe distances of π−π and d−d stacking in thin films. a

unit generally affect the LUMO and HOMO energy levels of polymers.37 2DFPE and 3DFPE have high-lying frontier energy levels though they respectively own two fluorine substituents with strong electron-withdrawing properties. Thus, the two building blocks still act as electron-donating units in their derived copolymers. Or in other words, two fluorinated diphenylethene moieties mainly affect the HOMO energy levels of polymers but have less influence on the LUMO energy levels. In general, the frontier orbital energy levels of the polymers match well with the Fermi level (5.13 eV) of an Au electrode and are in favor of hole injections from the Au electrode to polymer layers.

during negative and positive scans. The oxidative peaks are much stronger than their reductive counterparts, indicating that these copolymers are more easily oxidized than reduced. Based on the respective onset oxidation potentials (EOx Onset) of ca. 1.00 and 0.92 V versus Ag/AgCl, the HOMO energy levels were estimated to be ca. −5.40 eV for P2DFPE-n and −5.32 eV for P3DFPE-n calculated by the equation of EHOMO = −(4.4 + 36 Similarly, the LUMO energy levels of P2DFPE-n EOx Onset) eV. and P3DFPE-n were both estimated to be ca. −3.60 eV according to the almost equal onset reductive potentials (Ered Onset) of −0.80 V and the equation of ELOMO = −(4.4 + Ered Onset) eV. In donor−acceptor copolymers, the LUMO energy level of an acceptor unit and HOMO energy level of a donor E

DOI: 10.1021/acs.macromol.6b00144 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules

Figure 5. AFM topography images of thin films on OTS-modified SiO2/Si substrates: (a) P2DFPE-1, (b) P2DFPE-2, (c) P2DFPE-3, (d) P3DFPE1, (e) P3DFPE-2, and (f) P3DFPE-3. All the thin films were annealed at 180 °C except P3DFPE-2 (160 °C). All images are 5 μm × 5 μm in size.

Figure 6. 2D-GXRD patterns of (a) P2DFPE-1, (b) P2DFPE-2, (c) P2DFPE-3, (d) P3DFPE-1, (e) P3DFPE-2, and (f) P3DFPE-3 film after thermal annealing at 180 °C except P3DFPE-2 (160 °C). All polymers display lamellar packing (λ = 2d sin θ = 1.24 Å).

P3DFPE-1, 0.35 and 0.28 cm2 V−1 s−1 for P3DFPE-2, and 0.34 and 0.28 cm2 V−1 s−1 for P3DFPE-3, respectively (Table 2). It is important to note that the square roots of drain current vs gate-source voltage in the typical transfer plots of all copolymers are not linear. The above mobilities are all calculated from the main, linear regions at low gate voltage. For well illustrating the structure−property relationships and avoiding mobility overestimation as Sirringhaus indicated,1b therefore we also calculated the mobilities based on the linear regions at higher gate voltage. In this case, P2DFPE-n (n = 1, 2, and 3) exhibits mobilities of 0.27, 0.32, and 0.46 cm2 V−1 s−1, respectively, while P3DFPE-n (n = 1, 2, and 3) affords mobilities of 0.11, 0.06, and 0.09 cm2 V−1 s−1, respectively. The

Field-Effect Transistor Fabrication and Measurements. Bottom contact/bottom gate configuration was used to evaluate the carrier transport properties of P2DFPE-n and P3DFPE-n. The active polymers layer was deposited on octadecyltrichlorosilane (OTS)-treated SiO2 (300 nm)/n++-Si substrate by spin-coating a polymer solution (10 mg/mL in odichlorobenzene) at 2000 rpm for 40 s. All copolymers show ptype characteristics, and the typical output and transfer plots are presented in Figure 4 as well as Figures S4 and S5. After annealing at optimal temperatures for 20 min, the highest and average mobility is 1.36 and 0.99 cm2 V−1 s−1 for P2DFPE-1, 1.48, and 1.18 cm2 V−1 s−1 for P2DFPE-2, and 1.41 and 0.78 cm2 V−1 s−1 for P2DFPE-3, while 0.23 and 0.18 cm2 V−1 s−1 for F

DOI: 10.1021/acs.macromol.6b00144 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules

moreover, we can summarize that different fluorination positions and alkyl side chains exert great impact on thin film morphology and molecular packing of these copolymers.

gate voltage dependent mobilities of in P2DFPE-n and P3DFPE-n (n = 1, 2, and 3) are shown in Figure S6. The results also indicate that P2DFPE-n have higher hole mobilities than P3DFPE-n. These observations seem to defy the planarity of polymeric conjugated backbones of P2DFPE-n and P3DFPE-n because highly planar conjugated backbones could enlarge the overlapping areas between π-orbitals, which is thought to be beneficial for charge carrier transport.17 Nonetheless, previous studies also noticed that different backbone conformations can lead to different device performance.26,27 Thus, the low hole mobilities of P3DFPE-n could be attributed to inhomogeneous polymer backbone conformations induced by F···H−C and F···S conformational locks. The kind of conjugated backbone leads to lower-ordered molecular packing in thin film and thus low charge transport properties. Thin Film Microstructural Characterization. For better understanding the correlation between material structures and thin film performances, tapping-mode atomic force microscopy (AFM) and two-dimensional grazing incidence X-ray diffraction (2D-GXRD) were performed to investigate the microstructures of P2DFPE-n and P3DFPE-n thin films casted on OTSmodified SiO2 substrates. Figure 5 shows the AFM images of the annealed P2DFPE-n and P3DFPE-n thin films. The P2DFPE-n thin films have fiber-like intercalating networks with obviously crystallized zones. With the extension of alkyl chains and branched point of alkyl chains moving away from πconjugated D−A cores, the crystallized grains become larger while grain boundaries are also slightly deeper. Crystallized grains and intercalating thin film morphologies are favorable for charge carrier transport while large grain boundaries result in trapping of charge carriers.13 Nonetheless, the P3DFPE-n thin films exhibit dense and smooth structure, which are composed of dense polymer microparticles. Figure 6 presents the 2D-GXRD images of these thin films. The relevant crystallographic parameters are summarized in Table 2. As shown in Figures 6a and 6b, the P2DFPE-1 and P2DFPE-2 thin films show strong Bragg peaks of (100), (200), (300), and even (400) in out-of-plane diffractions patterns and distinct and sharp Bragg peaks of (010) in in-plane diffractions pattern. P2DFPE-3 only displays slightly weak Bragg peaks of (h00) and (010) in out-of-plane or in-plane diffraction pattern, presumably resulting from the longer alkyl side chains (Figure 6c). Because no Bragg peaks of (h00) were observed in in-plane patterns, it can be concluded that P2DFPE-n (n = 1, 2, and 3) takes predominantly edge-on oriented respective to the OTSmodified SiO2/Si substrates and possess crystalline, highly ordered lamellar packing, and strong interchain interactions in the thin films.38 On the basis of the locating positions (qz and qxy) of (100) and (010), their d−d and π−π stacking distances were estimated to be 20.67 and 3.68 Å for P2DFPE-1, 21.73 and 3.59 Å for P2DFPE-2, and 22.34 and 3.59 Å for P2DFPE-3, respectively, whereas P3DFPE-n (n = 1, 2, and 3) all own comparatively random close packing modes in solid state.39 Their Bragg peaks of (h00) appear in both out-of-plane and inplane orientations, and semicircular (010) peaks also exist in 2D-GXRD images (Figure 6d−f). Based on their respective (qxy) of (100) and (010), the d−d and π−π distances were estimated to be 19.96 and 3.61 Å for P3DFPE-1, 23.37 and 3.62 Å for P3DFPE-2, and 23.07 and 3.48 Å for P3DFPE-3, respectively. These observations could well explain their different charge transport properties in PFET devices because ordered molecular packing mode is thought to be favorable for charge carrier transport.15 In combination with AFM images,

■

CONCLUSIONS We have developed two difluorodiphenylethene-based building blocks, 2DFPE and 3DFPE, based on which a series of D−A copolymers, P2DFPE-n and P3DFPE-n, were designed and synthesized. The two kinds of copolymers display different backbone conformations, photophysical properties, frontier orbital energy levels, and intra- and intermolecular interactions. P3DFPE-n containing F···H−C and F···S conformational locks have more planar conjugated backbones than those of P2DFPE-n containing F···H−C conformational locks. Nonetheless, P2DFPE-n exhibits higher hole mobilities of 1.3−1.5 cm2 V−1 s−1, whereas P3DFPE-n affords low mobilities of 0.2− 0.4 cm2 V−1 s−1 in solution-processed PFETs. Thin film microstructure investigations reveal that P2DFPE-n prefers crystalline and highly ordered thin films with lamella molecular packing, while P3DFPE-n presents random close molecular packing mode in solid state. These results highlight that different fluorination positions can induce different noncovalent intramolecular interactions and backbone conformations, which have important influences on tuning the electronic properties of semiconducting polymers.

■

EXPERIMENTAL SECTION

General Procedures and Requirements. All chemicals were purchased from Sigma-Aldrich or other commercial sources and used without further purification if not specified otherwise. Anhydrous solvents, such as tetrahydrofuran (THF) and 1,4-dioxane, were freshly distilled over sodium wire/benzophenone. All reactions were carried out using the Schlenk technique in Ar. Measurements and Characterization. Proton nuclear magnetic resonance (1H NMR) spectra and carbon nuclear magnetic resonance (13C NMR) spectra of synthetic intermediates were recorded on Bruker Fourier 300 NMR spectrometers. High temperature 1H NMR spectra of polymers were recorded on a Bruker DMX 300 NMR spectrometer at 100 °C. High resolution mass spectroscopy (HRMS) measurements were collected using electron-impact mass spectra (EIMS) on a Bruker BIFLEX III mass spectrometer. High temperature gel permeation chromatography (GPC) analyses were performed on a Polymer Laboratories PL 220 system using a refractive index detector at 150 °C and using 1,2,4-trichlorobenzene as the eluent with polystyrenes as standards. Elemental analyses were carried on a CARLO ERBA 1106 elemental analyzer. Thermaogravimetric analysis (TGA) measurements were carried out on a PerkinElmer series 7 thermal analysis system under N2 at a heating rate of 10 °C min−1. Optical properties of all synthesized polymers were measured using a Hitachi U-3010 spectrophotometer. Electrochemical property measurements were recorded on an electrochemistry workstation with a conventional three-electrode configuration. The platinum stick electrode coated with a thin film layer of polymer was used as working electrode. Ag/AgCl electrode was used as the reference electrode, and platinum wire was used as the counter electrode. An anhydrous and N2-saturated solution of 0.1 M tetrabutylammonium hexylfluorophosphate in acetonitrile was used as the supporting electrolyte. Thin film morphologies were analyzed in air using a Digital Instruments Nanoscope V atomic force microscope operated in tapping mode. AFM samples were identical to those used in FET performance analysis. The grazing incidence X-ray diffraction (GXRD) data were obtained by illuminating the thin film samples at a constant incidence angle of 0.2°. (E)-1,2-Bis(4′-bromo-2′-fluorophenyl)ethene (2). To a stirred suspension of zinc powder (5.0 g, 75 mmol) in dry THF (80 mL), TiCl4 (4.2 mL, 38 mmol) was added slowly at −10 °C. The resulting G

DOI: 10.1021/acs.macromol.6b00144 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules

1.78. Anal. Calcd for C76H112F2N2O2S2: C, 76.98; H, 9.35; N, 2.36. Found: C 75.99, H 9.49, N 2.49. P2DFPE-2 (223 mg, 94%). 1H NMR (300 MHz, C2D2Cl4, δ): 8.78−8.26 (br, 12H), 5.39−4.92 (br, 4H), 2.81−2.05 (br, 94H). GPC: Mn = 80.2 kDa, Mw = 197.8 kDa, PDI = 2.46. Anal. Calcd for C76H112F2N2O2S2: C, 76.98; H, 9.35; N, 2.36. Found: C 75.94, H 9.37, N 2.45. P2DFPE-3 (220 mg, 91%). 1H NMR (300 MHz, C2D2Cl4, δ): 8.60−8.32 (br, 12H), 5.38−4.87 (br, 4H), 2.80−2.06 (br, 98H). GPC: Mn = 34.5 kDa, Mw = 106.5 kDa, PDI = 3.08. Anal. Calcd for C78H116F2N2O2S2: C, 77.18; H, 9.47; N, 2.31. Found: C 75.27, H 9.46, N 2.38. P3DFPE-1 (213 mg, 90%). 1H NMR (300 MHz, C2D2Cl4, δ): 10.22−10.20 (br, 2H), 8.92−8.09 (br, 10H), 5.27−5.07 (br, 4H), 2.80−2.05 (br, 94H). GPC: Mn = 23.9 kDa, Mw = 75.5 kDa, PDI = 3.14. Anal. Calcd for C76H112F2N2O2S2: C, 76.98; H, 9.35; N, 2.36. Found: C 76.09, H 9.15, N 2.36. P3DFPE-2 (211 mg, 89%). 1H NMR (300 MHz, C2D2Cl4, δ): 10.29−10.20 (br, 2H), 8.93−8.23 (br, 10H), 5.32−5.12 (br, 4H), 2.80−2.05 (br, 94H). GPC: Mn = 17.2 kDa, Mw = 36.1 kDa, PDI = 2.09. Anal. Calcd for C76H112F2N2O2S2: C, 76.98; H, 9.35; N, 2.36. Found: C 75.01, H 9.13, N 2.30. P3DFPE-3 (228 mg, 94%). 1H NMR (300 MHz, C2D2Cl4, δ): 10.08−10.03 (br, 2H), 8.95−8.22 (br, 10H), 5.39−4.93 (br, 4H), 2.81−2.06 (br, 98H). GPC: Mn = 20.8 kDa, Mw = 45.4 kDa, PDI = 2.18. Anal. Calcd for C78H116F2N2O2S2: C, 77.18; H, 9.47; N, 2.31. Found: C 76.32, H 9.27, N 2.29. X-ray Crystallography. X-ray crystallographic data were collected with a Bruker Smart CCD diffractometer through using graphitemonochromated Mo Kα radiation (λ = 0.710 73 Å). The data were collected at 173 K using ω scan in the θ range of 3.172°−27.459°. A total of 4120 reflections were measured, of which 1405 were independent reflections [R(int) = 0.0345]. The structures were resolved by the direct method and refined by full-matrix least-squares on F2 using the SHELXL-97 program. All non-hydrogen atoms were refined anisotropically, and all hydrogen atoms were placed using AFIX instructions. Crystallographic data for single crystal of 2DFPEbased intermediate 2: C14H8Br2F2; FM = 374.02; crystal size 0.35 × 0.2 × 0.16 mm3; triclinic; P-1; a = 4.037(2) Å; b = 5.968(3) Å; c = 13.092(6) Å; a = 79.090(13)°; b = 87.090(15)°; g = 85.960(14)°; Z = 1; ρcalculated = 2.012 g/cm3. The refinement was converged to R1 = 0.0278 for I > 2σ(I), R1 = 0.0290, wR2 = 0.0684, GOF = 1.145 for all data. CCDC-1400987 contains the supplementary crystallographic data. Fabrication and Performance of the PFETs. Bottom-gate/ bottom-contact (BGBC) field-effect transistor devices were fabricated using n++-Si/SiO2 (300 nm) substrates where n++-Si and SiO2 were used as the gate electrode and gate dielectric, respectively. Gold/ titanium (30 nm/5 nm) was fabricated as source and drain electrodes by a photolithography technique. After being fully cleaned by ultrasonication in acetone, deionized water, and ethanol and subsequently dried under vacuum at 80 °C, the silica substrates were modified with octadecyltrichlorosilane to form an OTS selfassembled monolayer on the surface of silica substrates. The polymeric semiconducting layer was fabricated on the OTS-treated substrate by spin-coating a DPE-based polymer solution (10 mg/mL) at 2000 rotations/min. The polymer solution was prepared by dissolving the polymer in o-dichlorobenzene and stirring at 110 °C for 24 h. The resulting thin film devices were optionally thermal annealed at 180 or 160 °C for 20 min in ambient conditions. The PFFT devices have a channel length (L) of 50 or 20 μm and a channel width (W) of 1400 μm. A Keithley 4200 SCS semiconductor parameter analyzer on a probe stage was employed to evaluate device performance in ambient air. The carrier mobility, μ, was calculated from the data in the saturated regime according to the equation

mixture was heated to reflux and stirred for 2 h under Ar. Then, a solution of 1 (2.7 g, 13.5 mmol) in of dry THF (50 mL) was added dropwise while the mixture was refluxed and stirred overnight. The solution was quenched with saturated aqueous NaHCO3 solution and extracted with ethyl acetate. The extract was washed with brine, dried over MgSO4, filtered, and concentrated to crude product as a white solid. After being further recrystallized from ethyl acetate, the title compound was obtained as a white solid (2.2 g, 90%). 1H NMR (300 MHz, CDCl3, δ): 7.48−7.42 (m, 2H), 7.22 (d, J = 2.1 Hz, 1H), 7.27− 7.25 (m, 2H), 7.23 (d, J = 1.8 Hz, 1H), 7.21 (s, 2H). 13C NMR (75 MHz, CDCl3, δ): 161.7, 158.3, 127.98, 127.92, 127.69, 127.64, 124.01, 123.85, 122.56, 122.51, 122.45, 121.76, 121.63, 119.66, 119.32. HRMS: Calcd for [M+]: 371.8961, 373.8940, 375.8920. Found: 371.8954, 373.8939, 375.8925. (E)-1,2-Bis(2′-fluoro-4′-(4″,4″,5″,5″-tetramethyl-1″,3″,2″-dioxaborolan-2′-yl)phenyl)ethene (3). To a mixture of 2 (1.87 g, 5.0 mmol), bis(pinacolato)diboron (2.9 g, 11.4 mmol), and KOAc (2.9 g, 29 mmol) were added PdCl2(dppf) (730 mg, 0.88 mmol) and degassed anhydrous 1,4-dioxane (20 mL). The resulting suspension were heated to 80 °C and stirred for 48 h under Ar. After being cooled to rt, the reaction mixture was poured on a short silica gel pad to remove the catalyst using ethyl acetate as eluent. The filtration was washed with water and brine, dried over Na2SO4, and concentrated in vacuo. The crude residual was purified by silica gel chromatography by ethyl acetate/hexane and recrystallization from ethyl acetate to give the desired compound as a white solid (1.0 g, 43%). 1H NMR (300 MHz, CDCl3, δ): 7.66−7.61 (m, 2H), 7.57−7.55 (m, 2H), 7.51 (s, 1H), 7.48 (s, 1H), 7.42 (s, 2H), 1.35 (s, 24H). 13C NMR (75 MHz, CDCl3, δ): 161.8, 158.5, 130.40, 130.36, 127.63, 127.47, 126.43, 126.40, 123.86, 123.81, 123.75, 121.71, 121.43, 84.09, 24.84. HRMS Calcd for [M+]: 468.2455. Found: 468.2450. (E)-1,2-Bis(4′-bromo-3′-fluorophenyl)ethene (5). The synthetic method of 2 was followed using 4 (2.7 g, 13.5 mmol) to give the title compound as a colorless solid (2.1 g, 87%). 1H NMR (300 MHz, CDCl3, δ): 7.55 (dd, J = 7.5 Hz, J = 6.6 Hz, 2H), 7.27 (dd, J = 7.0 Hz, J = 2.0 Hz 2H), 7.15 (dd, J = 7.0 Hz, J = 2.0 Hz, 2H), 7.00 (s, 2H). 13C NMR (75 MHz, CDCl3, δ): 161.02, 157.74, 138.15, 138.06, 133.75, 128.44, 128.41, 123.61, 123.56, 114.13, 113.82, 108.57, 108.29. HRMS: Calcd for [M+]: 371.8961, 373.8940, 375.8920. Found: 371.8962, 373.8936, 375.8920. (E)-1,2-Bis(3′-fluoro-4′-(4″,4″,5″,5″-tetramethyl-1″,3″,2″-dioxaborolan-2′-yl)phenyl)ethene (6). The synthetic method of 3 was followed using 5 (1.87 g, 5.0 mmol) to give the title compound as a white solid (1.0 g, 44%). 1H NMR (300 MHz, CDCl3, δ): 7.75 (dd, J = 7.5 Hz, J = 6.6 Hz, 2H), 7.28 (dd, J = 7.5 Hz, J = 0.9 Hz, 2H), 7.19 (dd, J = 10.5 Hz, J = 0.9 Hz, 2H), 7.11 (s, 2H), 1.37 (s, 24H). 13C NMR (75 MHz, CDCl3, δ): 169.21, 165.89, 142.15, 142.03, 137.21, 137.10, 129.55, 129.52, 122.15, 122.12, 112.99, 112.66, 83.89, 24.80. HRMS: Calcd for [M+]: 468.2455; Found: 468.2448. General Synthetic and Purification Procedure of P2DFPE-n and P3DFPE-n. To a 50 mL Schlenk tube were added 2Br-DPP (7, 8, or 9) (0.20 mmol), 2DFPE- or 3DFPE-based monomer, 3 or 6 (0.20 mmol), 2 M aqueous K2CO3 solution (2 mL), 2 drops of Aliquat 336, and toluene (15 mL). After the tube was charged with Ar through a freeze−pump−thaw cycle for several times, Pd2(dba)3 (6 mg) and P(o-tol)3 (17 mg) were added quickly in one portion. The mixture was heated to 90 °C and stirred for 48 h under Ar. A toluene solution of phenylboronic acid was added using a syringe, and then the mixture was stirred for an additional 4 h, followed by addition of a few drops of bromobenzene and stirring overnight. After being cooled to room temperature, the mixture was poured into 300 mL of methanol containing 5 mL of concentrated hydrochloric acid and stirred for a few hours. The resulting solid was filtered and subjected to Soxhlet extraction for 2 days in methanol, acetone, and hexane for the removal of low-molecular-weight and catalytic impurities. The remaining solid was extracted with chlorobenzene and precipitated again from methanol to give the desired polymer material. P2DFPE-1 (218 mg, 92%). 1H NMR (300 MHz, C2D2Cl2, δ): 10.14−10.02 (br, 2H) 8.65−8.34 (br, 10H), 5.35−4.88 (br, 4H), 2.80−1.82 (br, 94H). GPC: Mn = 35.3 kDa, Mw = 63.2 kDa, PDI =

IDS = H

⎛W ⎞ 2 ⎜ ⎟C μ(V − V ) T ⎝ 2L ⎠ i G DOI: 10.1021/acs.macromol.6b00144 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules where IDS is the saturation drain current, W/L is the channel width/ length, Ci is the capacitance per unit area of the gate dielectric layer, and VG and VT are the gate voltage and threshold voltage, respectively.

■

Wienk, M. M.; Janssen, R. A. J.; Anthopoulos, T.; Sirringhaus, H.; Heeney, M.; McCulloch, I. J. Am. Chem. Soc. 2011, 133, 3272−3275. (7) (a) McCulloch, I.; Heeney, M.; Chabinyc, M. L.; DeLongchamp, D.; Joseph Kline, R.; Cölle, M.; Duffy, W.; Fischer, D.; Gundlach, D.; Hamadani, B.; Hamilton, R.; Richter, L.; Salleo, A.; Shkunov, M.; Sparrowe, D.; Tierney, S.; Zhang, W. M. Semiconducting Thienothiophene Copolymers: Design, Synthesis, Morphology, and Performance in Thin-Film Organic Transistors. Adv. Mater. 2009, 21, 1091−1109. (b) Cheng, S.-W.; Tsai, C.-E.; Liang, W.-W.; Chen, Y.-L.; Cao, F.-Y.; Hsu, C.-S.; Cheng, Y.-J. Angular-Shaped 4, 9-Dialkylnaphthodithiophene-Based Donor−Acceptor Copolymers for Efficient Polymer Solar Cells and High-Mobility Field-Effect Transistors. Macromolecules 2015, 48, 2030−2038. (8) (a) Nakano, M.; Osaka, I.; Takimiya, K. Naphthodithiophene Diimide (NDTI)-Based Semiconducting Copolymers: From Ambipolar to Unipolar n-Type Polymers. Macromolecules 2015, 48, 576−584. (b) Yun, H.-J.; Cho, J.; Chung, D. S.; Kim, Y.-H.; Kwon, S.-K. Comparative Studies on the Relations between Composition Ratio and Charge Transport of Diketopyrrolopyrrole-Based Random Copolymers. Macromolecules 2014, 47, 7030−7035. (9) (a) Lee, W.-H.; Son, S. K.; Kim, K.; Lee, S. K.; Shin, W. S.; Moon, S.-J.; Kang, I.-N. Synthesis and Characterization of New SelenopheneBased Donor−Acceptor Low-Bandgap Polymers for Organic Photovoltaic Cells. Macromolecules 2012, 45, 1303−1312. (b) Shi, S. W.; Xie, X. D.; Gao, C.; Shi, K. L.; Chen, S.; Yu, G.; Guo, L. H.; Li, X. Y.; Wang, H. Q. Synthesis and Characterization of Angular-Shaped Naphtho [1, 2-b;5, 6-b′] difuran−Diketopyrrolopyrrole-Containing Copolymers for High-Performance Organic Field-Effect Transistors. Macromolecules 2014, 47, 616−625. (10) Subramaniyan, S.; Kim, F. S.; Ren, G.; Li, H.; Jenekhe, S. A. High Mobility Thiazole−Diketopyrrolopyrrole Copolymer Semiconductors for High Performance Field-Effect Transistors and Photovoltaic Devices. Macromolecules 2012, 45, 9029−9037. (11) Deng, Y. F.; Chen, Y. G.; Zhang, X. J.; Tian, H. K.; Bao, C.; Yan, D. H.; Geng, Y. H.; Wang, F. S. Donor−Acceptor Conjugated Polymers with Dithienocarbazoles as Donor Units: Effect of Structure on Semiconducting Properties. Macromolecules 2012, 45, 8621−8627. (12) (a) Kang, I.; Yun, H. J.; Chung, D. S.; Kwon, S. K.; Kim, Y. H. Record High Hole Mobility in Polymer Semiconductors via SideChain Engineering. J. Am. Chem. Soc. 2013, 135, 14896−14899. (b) (a) Kang, I.; An, T. K.; Hong, J. A.; Yun, H. J.; Kim, R.; Chung, D. S.; Park, C. E.; Kim, Y. H.; Kwon, S. K. Effect of Selenophene in a DPP Copolymer Incorporating a Vinyl Group for High-Performance Organic Field-Effect Transistors. Adv. Mater. 2013, 25, 524−528. (13) (a) Chen, H. J.; Guo, Y. L.; Yu, G.; Zhao, Y.; Zhang, J.; Gao, D.; Liu, H. T.; Liu, Y. Q. Highly π-Extended Copolymers with Diketopyrrolopyrrole Moieties for High-Performance Field-Effect Transistors. Adv. Mater. 2012, 24, 4618−4622. (b) Liu, X. T.; Guo, Y. L.; Ma, Y. Q.; Chen, H. J.; Mao, Z. P.; Wang, H. L.; Yu, G.; Liu, Y. Q. Flexible, Low-Voltage and High-Performance Polymer Thin-Film Transistors and Their Application in Photo/Thermal Detectors. Adv. Mater. 2014, 26, 3631−3636. (14) Lei, T.; Dou, J.-H.; Cao, X.-Y.; Wang, J.-Y.; Pei, J. ElectronDeficient Poly (p-phenylene vinylene) Provides Electron Mobility over 1 cm2 V−1 s−1 under Ambient Conditions. J. Am. Chem. Soc. 2013, 135, 12168−12171. (15) 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. H.; Su, H. B.; Ong, B. S. A Stable Solution-Processed Polymer Semiconductor with Record HighMobility for Printed Transistors. Sci. Rep. 2012, 2, 754. (16) Yun, H.-J.; Kang, S.-J.; Xu, Y.; Kim, S. O.; Kim, Y.-H.; Noh, Y.Y.; Kwon, S.-K. Dramatic Inversion of Charge Polarity in Diketopyrrolopyrrole-Based Organic Field-Effect Transistors via a Simple Mitrile Group Substitution. Adv. Mater. 2014, 26, 7300−7307. (17) (a) Coughlin, J. E.; Zhugayevych, A.; BakusII, R. C.; van der Poll, T. S.; Welch, D. C.; Teat, S. J.; Bazan, G. C.; Tretiak, S. A Combined Experimental and Theoretical Study of Conformational Preferences of Molecular Semiconductors. J. Phys. Chem. C 2014, 118, 15610−15623. (b) Nketia-Yawson, B.; Lee, H. S.; Seo, D.; Yoon, Y.;

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.6b00144. Figures S1−S6 and Table S1 (PDF) Intermediate 2 (CIF)

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (G.Y.). Author Contributions

W.F.Z. and K.L.S. contributed equally to this work. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was financially supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB12030100) and the National Natural Science Foundation of China (Grants 21474116 and 51233006). The GXRD tests were carried out at the BL16B1 Station of Shanghai Synchrotron Radiation Facility (SSRF), 1W1A station of Beijing Synchrotron Radiation Facility (BSRF), and 23A1 Station of National Synchrotron Radiation Research Centre (NSRRC, Taiwan). The authors gratefully thank the assistance of scientists from the stations during the experiments.

■

REFERENCES

(1) (a) Venkateshvaran, D.; Nikolka, M.; Sadhanala, A.; Lemaur, V.; Zelazny, M.; Kepa, M.; Hurhangee, M.; Kronemeijer, A. J.; Pecunia, V.; Nasrallah, I.; Romanov, I.; Broch, K.; McCulloch, I.; Emin, D.; Olivier, Y.; Cornil, J.; Beljonne, D.; Sirringhaus, H. Approaching Disorder-Free Transport in High-Mobility Conjugated Polymers. Nature 2014, 515, 384−388. (b) Sirringhaus, H. 25th Anniversary Article: Organic FieldEffect Transistors: The Path Beyond Amorphous Silicon. Adv. Mater. 2014, 26, 1319−1335. (2) Baeg, K. J.; Khim, D.; Kim, J.; Yang, B. D.; Kang, M.; Jung, S. W.; You, I. K.; Kim, D. Y.; Noh, Y. Y. High-Performance Top-Gated Organic Field-Effect Transistor Memory Using Electrets for Monolithic Printed Flexible NAND Flash Memory. Adv. Funct. Mater. 2012, 22, 2915−2926. (3) Zang, Y. P.; Zhang, F. J.; Huang, D. Z.; Gao, X. K.; Di, C.-A.; Zhu, D. B. Flexible Suspended Gate Organic Thin-Film Transistors for Ultra-Sensitive Pressure Detection. Nat. Commun. 2015, 6, 6269. (4) Zhang, F. J.; Zang, Y. P.; Huang, D. Z.; Di, C.-A.; Zhu, D. B. Flexible and Self-Powered Temperature-Pressure Dual-Parameter Sensors Using Microstructure-Frame-Supported Organic Thermoelectric Materials. Nat. Commun. 2015, 6, 8356. (5) Guo, X. G.; Ortiz, R. P.; Zheng, Y.; Kim, M. G.; Zhang, S. M.; Hu, Y.; Lu, G.; Facchetti, A.; Marks, T. J. Thieno[3, 4-c] pyrrole-4,6-dioneBased Polymer Semiconductors: Toward High-Performance, AirStable Organic Thin-Film Transistors. J. Am. Chem. Soc. 2011, 133, 13685−13697. (6) (a) Matsidik, R.; Komber, H.; Luzio, A.; Caironi, M.; Sommer, M. Defect-free Naphthalene Diimide Bithiophene Copolymers with Controlled Molar Mass and High Performance via Direct Arylation Polycondensation. J. Am. Chem. Soc. 2015, 137, 6705−6711. (b) Bronstein, H.; Chen, Z. Y.; Ashraf, R. S.; Zhang, W. M.; Du, J. P.; Durrant, J. R.; Tuladhar, P. S.; Song, K.; Watkins, S. E.; Geerts, Y.; I

DOI: 10.1021/acs.macromol.6b00144 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules Park, W. T.; Kwak, K.; Son, H. J.; Kim, B.; Noh, Y. Y. A Highly Planar Fluorinated Benzothiadiazole-Based Conjugated Polymer for HighPerformance Organic Thin-Film Transistors. Adv. Mater. 2015, 27, 3045−3052. (18) Chen, H. J.; Guo, Y. L.; Mao, Z. P.; Yu, G.; Huang, J. Y.; Zhao, Y.; Liu, Y. Q. Naphthalenediimide-Based Copolymers Incorporating Vinyl-Linkages for High-Performance Ambipolar Field-Effect Transistors and Complementary-Like Inverters under Air. Chem. Mater. 2013, 25, 3589−3596. (19) Zhang, W. F.; Liu, Y. Q.; Yu, G. Heteroatom Substituted Organic/Polymeric Semiconductors and their Applications in FieldEffect Transistors. Adv. Mater. 2014, 26, 6898−6904. (20) Lei, T.; Wang, J.-Y.; Pei, J. Roles of Flexible Chains in Organic Semiconducting Materials. Chem. Mater. 2014, 26, 594−603. (21) Lei, T.; Cao, Y.; Zhou, X.; Peng, Y.; Bian, J.; Pei, J. Systematic Investigation of Isoindigo-Based Polymeric Field-Effect Transistors: Design Strategy and Impact of Polymer Symmetry and Backbone Curvature. Chem. Mater. 2012, 24, 1762−1770. (22) Henson, Z. B.; Müllen, K.; Bazan, G. C. Design Strategies for Organic Semiconductors beyond the Molecular Formula. Nat. Chem. 2012, 4, 699−704. (23) Huang, H.; Chen, Z.; Ortiz, R. P.; Newman, C.; Usta, H.; Lou, S.; Youn, J.; Noh, Y. Y.; Baeg, K. J.; Chen, L. X.; Facchetti, A.; Marks, T. Combining Electron-Neutral Building Blocks with Intramolecular “Conformational Locks” Affords Stable, High-Mobility P- and NChannel Polymer Semiconductors. J. Am. Chem. Soc. 2012, 134, 10966−10973. (24) (a) Bronstein, H.; Frost, J. M.; Hadipour, A.; Kim, Y.; Nielsen, C. B.; Ashraf, R. S.; Rand, B. P.; Watkins, S.; McCulloch, I. Effect of Fluorination on the Properties of a Donor−Acceptor Copolymer for Use in Photovoltaic Cells and Transistors. Chem. Mater. 2013, 25, 277−285. (b) Jackson, N. E.; Savoie, B. M.; Kohlstedt, K. L.; de la Cruz, M. O.; Schatz, G. C.; Chen, L. X.; Ratner, M. A. Controlling Conformations of Conjugated Polymers and Small Molecules: The Role of Nonbonding Interactions. J. Am. Chem. Soc. 2013, 135, 10475−10483. (25) (a) Bronstein, H.; Hurhangee, M.; Fregoso, E. C.; Beatrup, D.; Soon, Y. W.; Huang, Z. G.; Hadipour, A.; Tuladhar, P. S.; Rossbauer, S.; Sohn, E.-H.; Shoaee, S.; Dimitrov, S. D.; Frost, J. M.; Ashraf, R. S.; Kirchartz, T.; Watkins, S. E.; Song, K.; Anthopoulos, T.; Nelson, J.; Rand, B. P.; Durrant, J. R.; McCulloch, I. Isostructural, Deeper Highest Occupied Molecular Orbital Analogues of Poly(3-hexylthiophene) for High-Open Circuit Voltage Organic Solar Cells. Chem. Mater. 2013, 25, 4239−4249. (b) Zhang, W. F.; Zheng, N. H.; Wei, C. Y.; Huang, J. Y.; Gao, D.; Shi, K. L.; Xu, J.; Yan, D. H.; Han, Y. C.; Yu, G. Vinylidenedithiophenmethyleneoxindole: A Centrosymmetric Building Block for Donor−Acceptor Copolymers. Polym. Chem. 2016, 7, 1413−1421. (26) Yum, S.; An, T. K.; Wang, X. W.; Lee, W.; Uddin, M. A.; Kim, Y. J.; Nguyen, T. L.; Xu, S. H.; Hwang, S.; Park, C. E.; Woo, H. Y. Benzotriazole-Containing Planar Conjugated Polymers with Noncovalent Conformational Locks for Thermally Stable and Efficient Polymer Field-Effect Transistors. Chem. Mater. 2014, 26, 2147−2154. (27) Lei, T.; Xia, X.; Wang, J.-Y.; Liu, C.-J.; Pei, J. Conformation Locked” Strong Electron-Deficient Poly(p-Phenylene Vinylene) Derivatives for Ambient-Stable n-Type Field-Effect Transistors: Synthesis, Properties, and Effects of Fluorine Substitution Position. J. Am. Chem. Soc. 2014, 136, 2135−2141. (28) Mao, Z. P.; Zhang, W. F.; Huang, J. Y.; Shi, K. L.; Gao, D.; Chen, Z. H.; Yu, G. High-Performance Polymer Field-Effect Transistors Fabricated with Low-Bandgap DPP-Based Semiconducting Materials. Polym. Chem. 2015, 6, 6457−6464. (29) Maeda, H.; Nishimura, K.-i.; Mizuno, K.; Yamaji, M.; Oshima, J.; Tobita, S. Synthesis and Photochemical Properties of Stilbenophanes Tethered by Silyl Chains. Control of (2π + 2π) Photocycloaddition, Cis−Trans Photoisomerization, and Photocyclization. J. Org. Chem. 2005, 70, 9693−9701. (30) Jeong, K. S.; Kim, S. Y.; Shin, U.-S.; Kogej, M.; Hai, N. T. M.; Broekmann, P.; Jeong, N.; Kirchner, B.; Reiher, M.; Schalley, C. A.

Synthesis of Chiral Self-Assembling Rhombs and Their Characterization in Solution, in the Gas Phase, and at the Liquid−Solid Interface. J. Am. Chem. Soc. 2005, 127, 17672−17685. (31) Zhang, M.; Tsao, H. N.; Pisula, W.; Yang, C.; Mishra, A. K.; Müllen, K. Field-Effect Transistors Based on a Benzothiadiazole− Cyclopentadithiophene Copolymer. J. Am. Chem. Soc. 2007, 129, 3472−3473. (32) Alvarez, S. A Cartography of the Van Der Waals Territories. Dalton Trans. 2013, 42, 8617−8636. (33) Ha, J. S.; Kim, K. H.; Choi, D. H. 2, 5-Bis(2-octyldodecyl)pyrrolo[3,4-c] pyrrole-1,4-(2 H, 5 H)-dione-Based Donor−Acceptor Alternating Copolymer Bearing 5,5′-Di(thiophen-2-yl)-2, 2′-biselenophene Exhibiting 1.5 cm2·V−1·s−1 Hole Mobility in Thin-Film Transistors. J. Am. Chem. Soc. 2011, 133, 10364−10367. (34) Cui, W.; Wudl, F. Dithienylbenzodipyrrolidone: New Acceptor for Donor−Acceptor Low Band Gap Polymers. Macromolecules 2013, 46, 7232−7238. (35) Ashraf, R. S.; Meager, I.; Nikolka, M.; Kirkus, M.; Planells, M.; Schroeder, B. C.; Holliday, S.; Hurhangee, M.; Nielsen, C. B.; Sirringhaus, H.; McCulloch, I. Chalcogenophene Comonomer Comparison in Small Band Gap Diketopyrrolopyrrole-Based Conjugated Polymers for High-Performing Field-Effect Transistors and Organic Solar Cells. J. Am. Chem. Soc. 2015, 137, 1314−1321. (36) Zhang, W. F.; Sun, X. N.; Xia, P. F.; Yu, G.; Wong, M. S.; Liu, Y. Q.; Zhu, D. B. Novel Butterfly-Shaped Fused Heteroacenes: Synthesis, Properties, and Device Performance of Solution-Processed Field-Effect Transistors. Org. Lett. 2012, 14, 4382−4385. (37) Park, J. H.; Jung, E. H.; Jung, J. W.; Jo, W. H. A Fluorinated Phenylene Unit as a Building Block for High-Performance n-Type Semiconducting Polymer. Adv. Mater. 2013, 25, 2583−2588. (38) Yoo, D.; Nketia-Yawson, B.; Kang, S.-J.; Ahn, H.; Shin, T. J.; Noh, Y.-Y.; Yang, C. A Timely Synthetic Tailoring of Biaxially Extended Thienylenevinylene-Like Polymers for Systematic Investigation on Field-Effect Transistors. Adv. Funct. Mater. 2015, 25, 586− 596. (39) Osaka, I.; Takimiya, K. Backbone Orientation in Semiconducting Polymers. Polymer 2015, 59, A1−A15.

J

DOI: 10.1021/acs.macromol.6b00144 Macromolecules XXXX, XXX, XXX−XXX