Donor–acceptor optoelectronic molecules based on hexa-peri-hexabenzocoronene and benzothiadiazole units: effect of different combinations

Accepted Manuscript Donor-acceptor optoelectronic molecules based on hexa-peri-hexabenzocoronene and benzothiadiazole units: effect of different combinations Long Liang, Xue-Qiang Chen, Li-Na Liu, Jun Ling, Xuan Xiang, Wen-Jing Xiao, CongWu Ge, Fu-Gang Zhao, Guanghui Xie, Zhengquan Lu, Jingjing Li, Wei-Shi Li PII:

S0040-4020(16)30489-6

DOI:

10.1016/j.tet.2016.05.072

Reference:

TET 27799

To appear in:

Tetrahedron

Received Date: 11 April 2016 Revised Date:

24 May 2016

Accepted Date: 30 May 2016

Please cite this article as: Liang L, Chen X-Q, Liu L-N, Ling J, Xiang X, Xiao W-J, Ge C-W, Zhao F-G, Xie G, Lu Z, Li J, Li W-S, Donor-acceptor optoelectronic molecules based on hexa-perihexabenzocoronene and benzothiadiazole units: effect of different combinations, Tetrahedron (2016), doi: 10.1016/j.tet.2016.05.072. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Donor-Acceptor Optoelectronic Molecules based on Hexa-peri-hexabenzocoronene and Benzothiadiazole Units: Effect of Different Combinations

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Long Lianga,b, Xue-Qiang Chenb,c, Jun Lingd, Xuan Xiangb,c, Wen-Jing Xiaoa,b, Cong-Wu Geb, Fu-Gang Zhaoc, Guanghui Xiea, Zhengquan Lua, Jingjing Lia and Wei-Shi Lia,b,c,*

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Tetrahedron journal homepage: www.elsevier.com

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Donor-Acceptor Optoelectronic Molecules based on Hexa-peri-hexabenzocoronene and Benzothiadiazole Units: Effect of Different Combinations Long Lianga,b, Xue-Qiang Chenb,c, Li-Na Liub, Jun Lingd, Xuan Xiangb,c, Wen-Jing Xiaoa,b, Cong-Wu Geb, Fu-Gang Zhaoc, Guanghui Xiea, Zhengquan Lua, Jingjing Lia and Wei-Shi Lia,b,c,* a

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Engineering Research Center of Zhengzhou for High Performance Organic Functional Materials, Zhongzhou University, 6 Yingcai Street, Huiji District, Zhengzhou 450044, China b Key Laboratory of Synthetic and Self-assembly Chemistry for Organic Functional Molecules, Shanghai Institute of Organic Chemistry, 345 Lingling road, Shanghai 200032, China c Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou 310018, China d Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310027, China

ABSTRACT

Article history: Received Received in revised form Accepted Available online

Three donor-acceptor (D-A) conjugated molecules using hexa-peri-hexabenzocoronene (HBC) as D unit while benzo[2,1,3]thiadiazole (BT) as A unit have been synthesized. They have different D-A combination fashions, including D-A, A-D-A and D-A-D. Their thermal, optical, electrochemical properties and molecular interactions have been thoroughly studied, with particular attention paid on the effect of different D-A combinations. Property comparison reveals that the ADA molecule using HBC as core and two BT units as arms possesses a better light absorption property and a more ordered film structure than the other two. Finally, such ADA molecule displayed the best field-effect transistor and photovoltaic performances.

Keywords: Optoelectronic molecules Hexa-peri-hexabenzocoronene Benzothiadiazole Field-effect transistors Photovoltaics

1. Introduction

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polycyclic aromatic hydrocarbon, hexa-peri-hexabenzocoronene (HBC), as electron-donating unit in combination with electronaccepting benzo[2,1,3]thiadiazole (BT) unit. HBC has a very

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With the advantages of flexibility, low cost and easy large scale fabrication, organic optoelectronic devices, including organic field effect transistors (OFETs) and organic photovoltaics (OPVs), have been one of hot research topics for decades.1 As a main class of their active materials, a variety of conjugated polymers and small molecules with different structures have been synthesized and investigated.1, 2 Among them, the materials composed of electron-donating (D) and electron-accepting (A) units have attracted particular attention because D/A combination can provide the following merits:3 (1) a broad light-harvesting spectrum by means of intramolecular charge transfer (ICT) and π-π* absorption bands; (2) much stronger intermolecular interactions, which are favorable for charge transport across the molecules; (3) an easy way to tune the frontier orbital energy levels of the material for suiting its particular application. Although a great effort has been made in the past, how to choose D and A units and how to combine them for construction of high performance materials still remain as open issues in the field.

2016 Elsevier Ltd. All rights reserved.

In this report, we present our recent effort in construction of D-A optoelectronic molecular materials by using a big discotic *Corresponding author. Tel: +86-21-54925381; Fax: +86-2154925381; E-mail: [email protected]

Fig. 1. Molecule structrues of HB, BHB and HBH.

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Scheme 1. Syntheses routes of HB, BHB and HBH.

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HB BHB HBH

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-1

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molecules using either diketopyrrolopyrrole or BT as acceptor were reported.6‒7 Their OPV cells showed the best efficiency around 1.6%. Herein, we focus more on their combination style than those published studies, and report three HBC-containing DA compounds, HB, BHB, and HBH (Fig. 1), having different D/A combinations. They showed different basic properties as well as photovoltaic and field-effect transistor performances. It is honest to point out similar combination between HBC and BT was reported by Müllen and co-workers during our work.8 However, our molecules possess additional thiophene spacer between BT and HBC for relieving their steric hindrance. Furthermore, HB and BHB molecules have terminal 3,4,5tridodecyloxy-substituted phenyl unit at BT side for improving their solubility. Compared with the reported work, these structural variations endowed the three molecules studied here with quite different optoelectronic properties and molecular packing structures.

800

Wavelength (nm)

Fig. 2. UV-vis absorption spectra of HB, BHB and HBH in both CHCl3 solutions and films.

large conjugated planar structure containing thirteen fused hexatomic rings, which generally leads to strong intermolecular π-π stacking. Up to now, numerous simple HBC derivatives have been developed for liquid crystals, OFETs, and OPVs.4‒7 As reported, they often self-assembled into columnar ordered structure and achieved high mobility therewith.4 Recently, HBC was combined with fluorine and dendritic thiophene moieties and proved a good photovoltaic performance with an efficiency up to 2.5%.5 For HBC-containing D-A materials, only two kinds of

2. Results and Discussion The syntheses of HB, BHB and HBH are outlined in Scheme 1. The key intermediates, mono- and bis-trimethyltinnylated 2,7bisthienylbenzothiadiazoles (19 and 4,10 respectively), mono- and di-brominated HBCs (HBC-Br111 and HBC-Br211) were obtained following literature methods. After Stille coupling of compound 1 with 5-bromo-1,2,3-tris(dodecyloxy)benzene,12 compound 2 was produced in a yield of 68%. Then, compound 2 was deprotonated with lithium 2,2,6,6-tetramethylpiperidide (LTMP) in THF and followed by reaction with Me3SnCl, giving another key intermediate 3 in a yield of 95%. Finally, Stille coupling of HBC-Br1 with 3 produced HB in a yield of 49%, while Stille coupling of HBC-Br2 with 3 and 4 afforded BHB and HBH in yields of 64% and 31%, respectively. All three compounds have good solubility in common solvents, such as toluene, CHCl3, chlorobenzene and dichlorobenzene. By means of thermogravimetric analysis (TGA) under N2, the three compounds were found to have good thermal stability with the 5%-weight loss temperatures (Td) of 345.8, 364.5, and 372.2 °C for HB, BHB, and HBH, respectively (Fig. S1). The UV-vis absorption spectra of HB, BHB and HBH were measured in CHCl3 solution and film state (Fig. 2 and Table 1). It was found that all three compounds have two main absorption bands. The band locating in longer wavelength region originates

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ACCEPTED MANUSCRIPT Table 1. The optical and electrochemical properties

HB

CHCl3a

film

368 (9.6), 518 (3.3)

372, 538

384(8.3), 542 (5.6)

BHB

Experimental

λFL, max b

384, 550

(nm)

Eox,onset (V) HOMO (eV)

622

0.53

-5.16

DFT Calculation

LUMO (eV) c

Eg,opt (eV) d

HOMO (eV)

LUMO (eV)

Eg (eV)

-3.18

1.91

-5.242

-2.976

2.266

636

0.65

-5.28

368 (8.8), 373, 628 0.53 -5.16 545 (3.0) 556 a Data in parentheses are molar absorption coefficients in a unit of 104 M-1 cm-1 b in 10-6 M CHCl3 solution, upon excited at 368 nm c LUMO = HOMO + Eg,opt d Eg,opt = 1240/λAbs, onset e cis form f trans form HBH

-3.38

1.85

-3.34

1.81

2.201 e

-5.216 f

-3.009 f

2.207 f

-5.192

-2.980

2.212

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e

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e

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750

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Fig. 3. Fluorescent spectra of HB, BHB and HBH in10-6 M and 10-5 M CHCl3 solutions upon excitation at 368 nm.

from ICT effect between electron-rich HBC and thiophene units and electron-deficient BT units, while the one in shorter wavelength region comes from local π-π* transition of conjugated moieties. As compared with those of HB at 368 and 518 nm, these two bands of BHB appeared at 384 and 542 nm, having 16 and 24 nm red-shift, respectively. In the case of HBH, the ICT band was further red-shifted to 545 nm and displayed the largest full width at half maximum (FWHM, 153 nm) among the family (106 nm for HB and 116 nm for BHB). Moreover, BHB displayed a maximum ICT band absorption coefficient, which is almost twice as those of HB and HBH. All these observations are well correlated to their structures and give the following information: (1) All three compounds have typical D-A lightabsorption features; (2) BHB is the best visible light absorber, which would benefit its photovoltaic application; (3) HBH possesses the strongest intermolecular interactions, which may be due to its two HBC units. Compared with the similar molecules

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Fig. 4. Cyclic voltammograms of HB, BHB and HBH films on glassy carbon electrodes in acetonitrile solutions containing 0.1 mol L-1 Bu4NPF6 electrolyte and with a scan rate of 50 mV s-1.

reported by Müllen and coworkers8 that exhibited a very weak ICT band, HB, BHB and HBH displayed a distinguished strong ICT band. This fact suggests that the insertion of thiophene unit between BT and HBC can effectively relieve the steric hindrance and enable a much better electron communication in the backbone. In film state, the ICT peaks of HB, BHB and HBH were measured to be 538, 550 and 556 nm, which are 20, 8 and 11 nm red-shifted to those in CHCl3 solutions, respectively (Fig. 2 and Table 1). Moreover, a shoulder appeared in the region of 560‒620 nm in the film absorption spectrum of HB. Such shoulder became much clearer around 582 nm in the case of BHB. All these observations suggest intermolecular interactions become stronger in all three compound films. Based on their film light-absorption onsets, the optical energy gaps (Eg,opt) were calculated to be 1.91, 1.85, and 1.81 eV for HB, BHB, and HBH, respectively, much smaller than those reported in reference [8]. Fluorescent spectra of HB, BHB and HBH were measured upon excitation at 368 nm in both 10-6 and 10-5 M CHCl3 solutions (Fig. 3). In the former dilute solutions, the fluoresecene peaks appeared at 622, 636 and 628 nm for HB, BHB and HBH, respectively. Moreover, the fluorescence intensity decreased following the order of HB > BHB > HBH. When the concentrations were increased 10 folds, the peaktops of these fluoresecence bands displayed at 627 (HB), 656 (BHB) and 638 nm (HBH), which were red-shifted 5, 20 and 10 nm, respectively. Besides, the peak intensities in 10-5 M solutions didn’t show ten

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Fig. 5. DFT computed molecular geometries and electron wave functions of HB, BHB and HBH

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times as those in 10-6 M solutions, only around 2.2-fold for HB, 0.8-fold for BHB and 1.8-fold for HBH. Such redshifts in fluorescence bands and their intensity changes clearly suggest the occurence of π-π intermolecular interactions among these molecules even in dilute solutions. And their interaction extents were highly dependent on molecules, in which HB exhibited the least, whereas BHB displayed the largest.

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Cyclic voltammetry (CV) was used to investigate electrochemical properties of HB, BHB and HBH (Fig. 4). The testings were performed on their film samples, which were prepared by casting their CHCl3 solutions onto glassy carbon electrodes. The onset oxidation potentials (Eox) vs. Ag/Ag+ were measured to be 0.53 V for both HB and HBH, while 0.66 V for BHB (Table 1). Under the same conditions, ferrocene/ferrocenium (Fc/Fc+) redox couple, which has a standard energy level of -4.8 eV from vacuum,13 was detected to be 0.17 V vs. Ag/Ag+. Therefore, the highest occupied molecular orbital (HOMO) energy levels of the investigated molecules can be calculated by the equation of HOMO = − e (Eox + 4.63). The results are -5.16 eV for HB and HBH, and -5.28 eV for BHB. Compared with those reported in reference [8] (< -5.60 eV), these HOMO orbitals stay at much high-lying levels. This should be one of impacts brought by the insertion of thiophene units. From their HOMO energy levels and Eg,opt, their lowest unoccupied molecular orbital (LUMO) energy levels were estimated to be 3.18 V for HB, -3.38 V for BHB and -3.34 V for HBH (Table 1). With two electron deficient BT units, BHB displays lower HOMO and LUMO energy levels than the other two molecules.

In order to understand the correlation between their chemical structures and optical and electrochemical properties, density functional theoretical calculation (DFT) was performed on these molecules at levels of B3LYP/6-311+G**//B3LYP/6-31G*14

with a GAUSSIAN03 program package.15 To simplify the computation, long side chains were replaced by methyl. Moreover, owing to non-straight bonding angle between 2- and 5- substitutions of thienyl units, BHB molecule possibly has two different structural configurations, one having two rigid arms in the same side of HBC central unit, while the other in the different side. Since it is similar to the case of the configuration isomers of vinyl compounds, these two configurations were named cisBHB and trans-BHB, respectively, and both subjected to DFT calculation.

As shown in Fig. 5, the optimized molecular geometries reveal that HBC units in all molecular configurations are in fully planar state. However, the whole molecular skeletons for all three compounds are twisting due to the presence of two kinds of big dihedral angles. One is between HBC plate and its neighbour thienyl unit, while the other is between the end phenyl and thienyl units. These two kinds of dihedral angles have similar values, both in the range of 24‒28 °. Furthermore, the calculated electron density wave functions (Fig. 5) reveal that the HOMO electron clouds of all the configurations delocalizes through the entire conjugated skeletons, while their LUMO electron clouds are mainly residing on BT units. This indicates the ICT characteristic for their HOMO-LUMO transition bands, and thus proves the D-A feature for all three compounds, coinciding with the observations in their UV-vis light absorption spectroscopy. From the calculated HOMO and LUMO energy levels and energy band gap (Eg) (Table 1), we can easily find that the cis form of BHB has almost similar values as its trans form. The fact suggests that the two configurations of BHB display almost the same energy stability and could exist together in reality. Although all three compounds have good solubility in chlorinated solvents, their 1H NMR experiments revealed the

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existence of severe intermolecular packing in their solutions. As shown in Fig. 6, 1H NMR of HB at 30 °C showed a few broad signals in aromatic region. Such broad signals gradually became sharper upon temperature rising and were well resolved at 90 °C. For example, the twelve protons of HBC rings appeared their NMR signals as 6 peaks in the range of 8.0‒8.7 ppm. While, those of BT protons were observed as one peak at 7.65 and those of thiophene units showed at 7.29, 7.87 and 7.96 ppm. For two protons of terminal benzene rings, their NMR signals presented at 6.92 ppm. In the case of BHB, 1H NMR at 30 °C displayed only one broad signal in the chemical shift range of 6‒8 ppm. After the temperature was elevated to 110 °C, the aromatic signals of BHB were clearly identified. Compared with HB, the proton signals in the aromatic region became less because of the symmetrical structure of BHB. Only three peaks around 8.19, 8.08, and 8.03 ppm were observed for the protons of HBC ring. The peak for BT proton shifted to 7.65 ppm, while those of thiophene protons changed to 7.17, 7.37, 7.89 and 7.98 ppm. The protons of terminal benzene showed up at 6.88 ppm. However for HBH, 1H NMR still exhibited broad aromatic signals even at 110 °C. These phenomena clearly indicate that intramolecular stacking takes place in all solutions of three compounds with the packing strength following an ascending order of HB < BHB < HBH. Moreover, the downshift of aromatic proton peaks and much more sharp shape of alkyl proton peaks than aromatic ones at low temperature observed in the 1H NMR spectra of HB and BHB suggest that strong intramolecular packing originates from their π-π interactions among their aromatic moieties. However, the situation is changed in the solid state. Differential scanning calorimetry (DSC) on solid samples (Fig. 7a) reveals that only BHB displayed clear phase transitions with

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Fig. 7. (a) DSC curves of HB, BHB and HBH at a heat ramping rate of 10 o C min-1 under N2. (b) XRD profiles of HB, BHB and HBH in films.

an endothermic peak at 202.5 °C and an exothermic peak at 192.8 °C in the second heating–cooling cycle. In comparison, a few weak and broad peaks were observed in the DSC profile of HB, and no obvious peak appeared in that of HBH in the temperature range of 0‒250 oC. These indicate that the BHB solid sample possesses a much ordered structure than HB and HBH. This is further confirmed by X-ray diffraction (XRD) experiments. As shown in Fig. 7b, BHB film XRD profile presented a series of peaks at 3.2, 6.6 and 9.7 ° with d-spacings of 2.68, 1.34 and 0.90 nm, respectively, assignable to 100, 200, and 300 reflections of a lamellar ordered structure with a layer distance of 2.68 nm. However, the film of HB did not display any obvious diffraction peaks, while only one peak around 3.2 ° with a d-spacing of 2.77 nm appeared in the XRD profile of HBH film. These suggest that the films of HB and HBH are amorphous or less ordered, which may be unfavorable for their optoelectronic applications. It is understandable that HB exhibited a less ordered structure than BHB since its unsymmetrical structure. However, it is curious that HBH displayed much stronger intermolecular interactions in solution than BHB, but showed a less ordered film. We deduce that the kinetical issue would be one of the important reasons, since many expamples have demonstrated quick precipitation usually results in a less ordered structure.16 Finally, the potential applications of these compounds were investigated as field-effect transistors and photovoltaic active materials. The OFET devices were fabricated by spin-coating their chlorobenzene solutions with a concentration of 8 mg mL-1 onto octadecyltrichlorosilane (OTS)-treated SiO2/Si substrates. After checking their I-V curves, the BHB-based device clearly showed typical OFET transfer curve (Fig. 8b). Estimated from

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PCE (%) 0.07 0.19 0.14

µOFET (cm2 V-1 s-1) 7.3×10-7 3.8×10-5 1.1×10-6

In this study, the investigation on how to construct high performance D-A optoelectronic molecules based on HBC as D while BT as A units have been carried out. Three compounds having different D/A combinations, namely DA, ADA and DAD, have been checked. It was found that that the molecule having a structure of ADA exhibits a much broader and stronger UV-vis absorption spectrum and more ordered film structures than the other two combinations. Finally, such molecule was proved with the best OFET and OPV performances among the family. However, since all the tested devices did not show the promising behaviors, how to design HBC-based D-A optoelectronic molecular materials with high performance still remains as a challenging task in the field. For its approaching, the present study would provide some helpful information.

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FF (%) 32.1 38.8 31.7

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3. Conclusions

JSC (mA cm-2) 0.36 0.74 0.63

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Table 2. The OFET and photovoltaic performances of three compounds

HB BHB HBH

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2 -

)

4 . 0

its linear region, the mobility was found to be 3.8 × 10-5 cm2 V-1 s-1 (Table 2). However, for the devices based on HB and HBH, no clear FET feature was observed (Fig. 8a and 8c). Their mobilities were detected to be 7.3 × 10-7 and 1.1 × 10-6 cm2 V-1 s-1, respectively. And we found that thermal annealing did not improve the performance of these OFET devices. Although all three devices did not show promising performance, the mobility of the BHB device is much higher than the other two. Moreover, photovoltaic performances of the compounds were investigated with solar cell devices having a configuration of ITO/PEDOT:PSS/active layer/LiF/Al. The active layers were fabricated by spin-coating from chlorobenzene solutions containing the checked compound (HB, BHB or HBH) and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) in a weight ratio of 1/2 and having a total concentration of 18 mg L-1. Before the deposition of top metal electrode, thermal annealing treatment was applied on all the devices at 100 °C for 10 min. After checking their I-V curves, one may disappoint that all these solar devices displayed poor performances with power conversion efficiencies (PCE) below 1% (Fig. 9 and Table 2). However, the comparison again shows that BHB-based device exhibited the best performance with an open-circuit voltage (VOC) of 0.66 V, a short-circuit current (JSC) of 0.74 mA cm-2, and a fill factor (FF) of 38.8%, giving a PCE of 0.19%. The better OFET and OPV performance that BHB devices exhibited would be correlated to its better and stronger visible light absorption property and more ordered lamellar film structure.

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Fig. 9. Current density‒voltage curves under the illumination of AM 1.5 G with a density of 100 mW cm‒2 of the solar cell devices based on HB, BHB, and HBH.

4. Experimental section 4.1. Measurements and Characterizations Unless indicated, all commercial reagents were used as received without further purification. Reaction solvents were dehydrated following standard methods, e.g. refluxing tetrahydrofuran (THF) and toluene over a mixture of Na and benzophenone under argon, and freshly distilled prior to use. 1H and 13C NMR spectra were recorded on a Varian Mercury spectrometer operated at 400 MHz and 100 MHz, respectively, using CDCl3 or CDCl2CDCl2 as a solvent and tetramethyl silane as an internal reference. Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectroscopy was carried out on a Shimadzu Biotech Axima Performance Mass Spectrometer using dithranol or α-cyano-4hydroxycinnamic acid as a matrix. UV-vis absorption and fluorescence spectroscopies were performed on a Hitachi U-3310 absorption spectrophotometer and a Hitachi F-4600 fluorescence spectrometer, respectively. Cyclic voltammetry (CV) was carried out on a CHI 660C electrochemical workstation with a glassy carbon working electrode, a platinum wire counter electrode and a Ag/AgNO3 reference electrode. The samples were casted from chloroform solutions on glassy carbon to form films, and then measured in CH3CN solution containing 0.1 M Bu4NPF6 supporting electrolyte at a scan rate of 50 mV s-1. Thermogravimetric analysis (TGA) was carried out by a Q500 TGA instrument under a N2 flow at a heating rate of 10 °C min-1. Differential scanning calorimetry (DSC) was measured on a

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8H), 8.08 (br, 2H), 7.96 (d, J = 4.4 Hz, 1H), 7.87 (t, J = 4,4 Hz, Q200 DSC instrument under a N2 flow at a heating and cooling MANUSCRIPT ACCEPTED 1H), 7.65 (br, 2H), 7.29 (br, 2H), 6.92 (br, 2H), 4.10 (t, J = 4.4 rate of 10 °C min-1. X-ray diffraction (XRD) was carried out on Hz, 4H), 4.05 (t, J = 4.4 Hz, 2H), 3.10 (m, 10H), 1.0‒2.2 (br, a PANalytical X’Pert Pro diffractometer using Cu Kα beam (40 160H), 0.87 (m, 24H). LRMS (MALDI) m/z: 2292.0 (M+). kV, 40 mA) in θ−2θ scans (0.033 Å and 30 s per step). HRMS (MALDI, m/z): [M+H]+ calcd. for C158H220N2O3S3, 4.2. Synthesis 2289.6311; found, 2289.6281. Precursor 1,9 4,10 HBC-Br1,11 HBC-Br2,11 and 5-bromo-1,2,3BHB. A mixture of compound 3 (118.0 mg, 0.108 mmol), tris(dodecyloxy)benzene12 were prepared following literature HBC-Br2 (48.6 mg, 0.036 mmol), Pd(PPh3)4 (4.2 mg, 0.0036 procedures. mmol) and toluene (10 mL) was subjected to degas by three

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cycles of freeze-pump-thaw and then heated to reflux overnight. Then, cold water was added and the resulted mixture was extracted with CHCl3 several times, dried over anhydrous MgSO4, and concentrated under a reduced pressure. The residue was subjected to silica gel column chromatography using DCM and then CHCl3 as an eluent. The crude product was purified by sizeexclusion chromatography with Bio-Beads S-X1 gel, affording 70.0 mg compound BHB as purple solid in a yield of 64%. 1H NMR (400 MHz, CDCl2CDCl2, 110 oC, δ): 8.19 (br, 4H), 7.92‒8.13(br, 10H), 7.89 (br, 2H), 7.65 (br, 4H), 7.37 (br, 2H), 7.17 (br, 2H), 6.88 (br, 4H), 4.00‒4.18 (m, 12H), 2.98 (br, 8H), 2.05 (m, 8H), 1.88 (m, 12H), 1.19‒1.77 (br, 180H), 0.92 (m, 30H). LRMS (MALDI) m/z: 3050.9 (M+). HRMS (MALDI, m/z): [M+H]+ calcd. for C202H278N4O6S6, 3047.9774; found, 3047.9890. HBH. A mixture of compound 4 (16.9 mg, 0.027 mmol), HBC-Br1 (85.6 mg, 0.0594 mmol), Pd(PPh3)4 (6.2 mg, 0.0054 mmol) and toluene (7 mL) was subjected to degas by three cycles of freeze-pump-thaw and then heated to reflux overnight. Then, cold water was added and the resulted mixture was extracted with CHCl3 several times, dried over anhydrous MgSO4, and concentrated under a reduced pressure. The residue was subjected to silica gel column chromatography using DCM and then hot CHCl3 as an eluent. The crude product was purified by size-exclusion chromatography with Bio-Beads S-X1 gel, affording 25.0 mg compound HBH as purple solid in a yield of 31%. 1H NMR was measure at 110 oC but did not show any resolved peaks. LRMS (MALDI) m/z: 3025.6 (M+). HRMS (MALDI, m/z): [M+H]+ calcd. for C218H280N2S3, 3022.1149; found, 3022.1128.

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4-(Thiophen-2-yl)-7-(5-(3,4,5-tris(dodecyloxy)phenyl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole (compound 2). To a mixture of compound 1 (225.0 mg, 0.48 mmol), 5-bromo-1,2,3tris(dodecyloxy)benzene (400.0 mg, 0.56 mmol) and toluene (10.0 mL), Pd(PPh3)4 (50.0 mg, 0.043 mmol) was added under Ar. After thoroughly degas by three cycles of freeze-pump-thaw, the reaction mixture was refluxed overnight under Ar. Then, cold water was added and the resulted mixture was extracted with dichloromethane (DCM) several times. The combined organic phase was washed with water, dehydrated over anhydrous MgSO4, and concentrated under a reduced pressure. The residue was subjected to silica gel column chromatography using a mixture of hexane and DCM as an eluent, affording 310 mg compound 2 as yellow solid in a yield of 68%. 1H NMR (400 MHz, CDCl3, δ): 8.13 (d, J = 4.0 Hz, 1H), 8.10 (d, J = 4.0 Hz, 1H), 7.89 (s, 2H), 7.46 (d, J = 4.8 Hz, 1H), 7.32 (t, J = 3.6 Hz, 1H), 7.22 (d, J = 4.8 Hz, 1H), 6.88 (s, 2H), 4.06 (t, J = 6.4 Hz, 4H), 4.00 (d, J = 6.4 Hz, 2H), 1.85 (m, 4H), 1.75 (m, 2H), 1.20‒1.55 (br, 54H), 0.88 (br, 9H). LRMS (MALDI) m/z: 928.5 (M+).

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4-(5-(Trimethylstannyl)thiophen-2-yl)-7-(5-(3,4,5-tris(dodecyl -oxy)phenyl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole (compound 3). A solution of compound 2 (130 mg, 0.14 mmol) in THF (15 mL) was cooled in dry-ice bath, and LTMP (226 mg, 1.0 mmol) in THF (0.5 mL) was added dropwisely under Ar. After the solution was warmed to room temperaure and cooled again, Me3SnCl (1.0 M, 1.1 mL) was added in one portion. After warming to room temperature slowly, the mixture was quenched by adding cold water (10 mL) and extracted with CH2Cl2 several times. The combined organic phase was washed with water, dehydrated over anhydrous MgSO4, and concentrated under a reduced pressure, affording 600 mg compound 3 as red solid in a yield of 95%. 1H NMR (400 MHz, CDCl3, δ): 8.18 (d, J = 3.6 Hz, 1H), 8.07 (d, J = 3.6 Hz, 1H), 7.86 (s, 2H), 7.29 (t, J = 3.6 Hz, 2H), 6.86 (s, 2H), 4.05 (t, J = 6.4 Hz, 4H), 3.98 (t, J = 6.4 Hz, 2H), 1.82 (m, 4H), 1.75 (m, 2H), 1.20‒1.55 (br, 54H), 0.86 (m, 9H), 0.42 (s, 9H). 13C NMR (100 MHz, CDCl3, δ): 153.73, 152.93, 152.78, 146.12, 145.25, 140.61, 138.74, 138.48, 136.38, 129.65, 128.71, 128.67, 126.12, 125.94, 125.88, 125.52, 123.96, 105.09, 73.87, 69.57, 32.22, 30.65, 30.05, 30.01, 29.96, 29.74, 29.68, 29.66, 26.42, 22.98, 14.40, -7.89. LRMS (MALDI) m/z: 1092.9 (M+). HRMS (MALDI, m/z): [M+H]+ calcd. for C59H92N2O3S3Sn, 1084.5324; found, 1084.5313. HB. Pd(PPh3)4 (4.7 mg, 0.004 mmol) was added into the solution of HBC-Br1 (57.6 mg, 0.04 mmol) and compound 3 (109.2 mg, 0.08 mmol) in toluene (6 mL) under Ar. The mixture was degassed by three cycles of freeze-pump-thaw, and heated to reflux overnight. Afterwards, cool water was added into the solution, and the mixture was extracted with CHCl3 three times. The organic phase was collected and washed by water, dehydrated over anhydrous MgSO4, and concentrated under a reduced pressure. The residue was subjected to silica gel column chromatography using DCM, and then CHCl3 as an eluent, affording 45 mg HB as red solid in a yield of 49%. 1H NMR (400 MHz, CDCl2CDCl2, 110 oC, δ): 8.66 (br, 2H), 8.25‒8.55 (br,

4.3. Device Fabrication and Characterization of OFET devices For OFET devices, the doped Si wafer with a SiO2 layer of 300 nm and a capacitance of 11 nF cm-2 was used as the gate electrode and dielectric layer. Prior to deposit active layer, SiO2/Si substrates were treated with octadecyltrichlorosilane (OTS) vapour. Afterward, the active layers were spin-coated with the solutions of HB, BHB and HBH (8 mg mL-1 in chlorobenzene). Finally, gold source and drain contacts (50 nm in thickness) were deposited by vacuum evaporation on top of the active layer through a shadow mask, affording a bottom-gate topcontact device configuration. The ratio between channel length (L) and width (W) was 8.95. Electrical measurements of OFET devices were carried out at room temperature in air using a Keithley 4200 semiconductor parameter analyzer. The fieldeffect mobility was calculated in the saturation regime by using the equation IDS = (µWCi/2L)(VG–VT)2, where IDS is the drainsource current, µ is the field-effect mobility, W is the channel width, L is the channel length, Ci is the capacitance per unit area of the gate dielectric layer, VG is the gate voltage, and VT is the threshold voltage. 4.4. Device Fabrication and Characterization of OPV devices The OPV devices were fabricated with a structure of ITO/PEDOT:PSS/active layer/LiF/Al. A thin layer of

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Tetrahedron

Acknowledgments 8. 9. 10.

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Financial support from National Natural Science Foundation of China (21474129), International Science & Technology Cooperation Program of China (2015DFG62680), Science and Technology Commission of Shanghai Municipality (13JC1407000), Zhejiang Provincial Natural Science Foundation of China (LQ15B040003), Science Foundation of Zhejiang SciTech University (14062074-Y), Chinese Academy of Sciences and Zhongzhou Univeristy are gratefully acknowledged. We also thank Professor Hongxiang Li, Professor Xike Gao, Ms. Simin Gao for their help in OFET measurements.

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References and notes

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a) Gunes, S.; Neugebauer, H.; Sariciftci, N. S. Chem. Rev. 2007, 107, 1324–1338; b) Cheng, Y.-J.; Yang, S.-H.; Hsu, C.-S. Chem. Rev. 2009, 109, 5868–5923; c) Arias, A. C.; MacKenzie, J. D.; McCulloch, I.; Rivnay, J.; Salleo, A. Chem. Rev. 2010, 110, 3–24; d) Wang, C.; Dong, H.; Hu, W.; Liu, Y.; Zhu, D. Chem. Rev. 2012, 112, 2208–2267. e) Dou, L.; You, J.; Hong, Z.; Xu, Z.; Li, G.; Street, R. A.; Yang, Y. Adv. Mater. 2013, 25, 6642–6671. a) Mishra, A.; Bäuerle, P. Angew. Chem. Int. Ed. 2012, 51, 2020– 2068; b) Li, C.; Wonneberger, H. Adv. Mater. 2012, 24, 613–636; c) Nielsen, C. B.; Turbiez, M.; McCulloch, I. Adv. Mater. 2013, 25, 1859–1880; d) Skabara, P. J.; Arlin, J.-B.; Geerts, Y. H. Adv. Mater. 2013, 25, 1948–1954; e) Roncali, J.; Leriche, P.; Blanchard, P. Adv. Mater. 2014, 1, 3821–3838; f) Wang, E.; Mammo, W.; Andersson, M. R. Adv. Mater. 2014, 26, 1801–1826. a) Coakley, K. M.; McGehee, M. D. Chem. Mater. 2004, 16, 4533–4542; b) Heeger, A. J. Chem. Soc. Rev. 2010, 39, 2354– 2371; c) Yuen, J. D.; Wudl, F. Energy Environ. Sci. 2013, 6, 392– 406; d) Wang, Y.; Liu, Y.; Chen, S.; Peng, R.; Ge, Z. Chem. Mater. 2013, 25, 3196–3204; e) Wang, Y.; Yang, F.; Liu, Y.; Peng, R.; Chen, S.; Ge, Z. Macromolecules, 2013, 46, 1368–1375; f) Ouyang, X.; Peng, R.; Ai, L.; Zhang, X.; Ge, Z. Nat. Photonics 2015, 9, 520–524.

AC C

2.

TE D

Supplementary data associated with this article can be found in the online version, at http://dx.doi.org/10.1016/xxxxxx.

1.

Wong, W. W. H.; Subbiah, J.; Puniredd, S. R.; Purushothaman, B.; Pisula, W.; Kirby, N.; Müllen, K.; Jones, D. J.; Holmes, A. B. J. Mater. Chem. 2012, 22, 21131–21137. Hinkel, F.; Cho, D.; Pisula, W.; Baumgarten, M.; Müllen, K. Chem. Eur. J. 2015, 21, 86–90. van Mullekom, H. A. M.; Vekemans, J. A. J. M.; Meijer, E. W. Macromolecules 2006, 39, 3262–3269. Fu, B.; Baltazar, J.; Hu, Z.; Chien, A.-T.; Kumar, S.; Henderson, C. L.; Collard, D. M.; Reichmanis, E. Chem. Mater. 2012, 24, 4123–4133. Ito, S.; Wehmeier, M.; Brand, J. D.; Kübel, C.; Epsch, R.; Rabe, J. P.; Müllen, K. Chem. Eur. J. 2000, 6, 4327–4342. Li, W.-S.; Yamamoto, Y.; Fukushima, T.; Saeki, A.; Seki, S.; Tagawa, S.; Masunaga, H.; Sasaki, S.; Takata, M.; Aida, T. J. Am. Chem. Soc. 2008, 130, 8886–8887. a) Li, Y.; Cao, Y.; Gao, J.; Wang, D.; Yu, G.; Heeger, A. J. Synth. Met. 1999, 99, 243–248; b) Zhang, J.; Cai, W.; Huang, F.; Wang, E.; Zhong, C.; Liu, S.; Wang, M.; Duan, C.; Yang, Y.; Cao, Y. Macromolecules 2011, 44, 894–901. a) Hohenberg, P.; Kohn, W. Phys. Rev. 1964, 136, B864–871; b) Kohn, W.; Sham, L. J. Phys. Rev. 1965. 140, A1133–1138; c) Becke, A. D. J. Chem. Phys. 1993, 98, 5648–5652; d) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. 1988, B37, 785–789. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A. J.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C. J. A. Pople, Gaussian 03, Gaussian, Inc., Wallingford CT, 2009. De Greef, T. F. A.; Smulders, M. M. J.; Wolffs, M.; Schenning, A. P. H. J.; Sijbesma, R. P.; Meijer, E. W. Chem. Rev. 2009, 109, 5687–5754.

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7.

RI PT

4. a) Piot, L.; Marchenko. A.; Wu, J.; Müllen, K.; Fichou, D. J. Am. PEDOT:PSS (Heraeus Clevios P VP. Al 4083) was spin-coated MANUSCRIPT ACCEPTED Chem. Soc. 2005, 127, 16245–16250; b) Yin, M.; Shen, J.; Pisula, on top of cleaned ITO glass at 6000 rpm and baked at 140 °C for W.; Liang, M.; Zhi, L.; Müllen, K. J. Am. Chem. Soc. 2009, 131, 15 min, affording a thickness of 23 nm. Then, the substrates 14618–14619; c) van de Craats, A. M.; Stutzmann, N.; Bunk, O.; were transferred into a N2-filled glove box. The active layer was Nielsen, M. M.; Watson, M.; Müllen, K.; Chanzy, H. D.; spin-coated from warm chlorobenzene solutions containing the Sirringhaus, H.; Friend, R. H. Adv. Mater. 2003, 15, 495–499; d) Shklyarevskiy, I. O.; Jonkheijm, P.; Stutzmann, N.; Wasserberg, checked compounds and PC61BM (Lumitec LT-8905). The D.; Wondergem, H. J.; Christianen, P. C. M.; Schenning, A. P. H. thermal anneal at desired temperature for 10 min if applied. J.; de Leeuw, D. M.; Tomović, Ž.; Wu, J.; Müllen, K.; Maan, J. C. Finally, a layer of LiF (1.0 nm) and a layer of Al (100 nm) were J. Am. Chem. Soc. 2005, 127, 16233–16237; e) Pisula, W.; -5 subsequently deposited in the vacuum of 10 mbar. The active Menon, A.; Stepputat, M.; Lieberwirth, I.; Kolb, U.; Tracz, A.; area of all devices is 7 mm2. Layer thickness was measured on a Sirringhaus, H.; Pakula, T.; Müllen, K. Adv. Mater. 2005, 17, 684–689. Veeco Dektak 150 profilometer. Current density-voltage (J-V) 5. Wong, W. W. H.; Ma, C.-Q.; Pisula, W.; Yan, C.; Feng, X.; Jones, curves were recorded with a Keithley 2420 source meter. D. J.; Müllen, K.; Janssen, R. A.; Bäuerle, P.; Holmes, A. B. Photocurrent was acquired upon irradiation using an AAA solar Chem. Mater. 2010, 22, 457–466. simulator (Oriel 94043A, 450 W) with AM 1.5G filter. The light 6. Wong, W. W. H.; Ma, C.-Q.; Pisula, W.; Mavrinskiy, A.; Feng, X.; -2 intensity was adjusted to be 100 mW cm using a NRELSeyler, H.; Jones, D. J.; Müllen, K.; Bäuerle, P.; Holmes, A. B. Chem. Eur. J. 2011, 17, 5549–5560. certified standard silicon cell (Orial reference cell 91150).

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