2,6-Diphenybenzo[1,2-b:4,5-b ]dichalcogenophens: A new class of high-performance

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1 2,6-Diphenybenzo[1,2-b:4,5-b ]dichalcogenophens: A new class of high-performance semiconductors for Organic Field-Effect Transistors Kazuo Takimiya,* Yoshihito Kunugi, Yasushi Konda, Naoto Niihara, Tetsuo Otsubo* Contents 1. Synthesis of DPh-BDT (1), DPh-BDS (2) and DPh-BDTe (3) 2. Device fabrication 3. XRD patters of AFM images of the evaporated files of References 1. Synthesis of DPh-BDT (1), DPh-BDS (2), and DPh-BDTe (3). General. All chemicals and solvents are of reagent grade unless otherwise indicated. All reactions were carried out under a nitrogen atmosphere. THF was purified by distillation from sodium benzophenone ketyl under nitrogen prior to use. Column chromatography was carried out with silica gel (Daisogel IR-60, µm). Melting points are uncorrected. Nuclear magnetic resonance spectra were obtained in deuterated chloroform with a JEOL Lambda 400 spectrometer operating at 400 MHz for 1 H and 100 MHz for 13 C with TMS as internal reference; chemical shifts (δ) are reported in parts per million. EI-MS spectra were obtained on a Shimadzu QP-2000 spectrometer using an electron impact ionization procedure (70 ev). The molecular ion peaks of the bromine-, selenium- or tellurium- containing compounds showed a typical isotopic pattern, and all the mass peaks are reported based on 79 Br, 80 Se, 130 Te. Caution: Selenium and tellurium are S1

2 highly toxic, and it is advisable to avoid direct contact with the skin. t-butyl lithium is pyrophoric; it must be handled with care. 1,4-Dibromo-2,5-bis(phenylethynyl)benzene (4) 1 To a degassed solution of 1,4-dibromo-2,5-diiodobenzene 1,2 (5.0 g, 10 mmol) in a diisopropyl amine (30 ml) and benzene (30 ml was subsequently added phenylacetylene (2.2 ml, 20 mmol), Pd(PPh 3 ) 4 (0.21 g, 0.3 mmol), and CuI (0.11 g, 0.58 mmol). The resulting mixture was stirred for 1 h at room temperature, then diluted with water (30 ml), and extracted with ether (30 ml 2). The extract was washed with water (30 ml x 2) and dried (MgSO 4 ). Evaporation of the solvent gave an oily residue, which was subjected to column chromatography on silica gel eluted with hexane-dichloromethane (3:1, v/v) to give 1,4-dibromo-2,5-bis(phenylethynyl)benzene as a colorless solid. Recrystallization from hexane gave colorless needles (3.0g, 70%); mp C; 1 H NMR δ (m, 6H), 7.58 (m, 4H), 7.79 (s, 2H); 13 C NMR δ 86.8, 96.6, 122.3, 123.7, 126.4, 128.4, 129.1, 131.8, 136.0; MS (EI) m/z 434 (M + ). Anal. Calcd for C 22 H 12 Br 2 : C, 60.59; H, Found: C, 60.48; H, ,6-Dipheny-benzo[1,2-b:4,5-b ]diselenophene (DPh-BDS, 2). To a solution of 1,4-dibromo-2,5-bis(phenylethynyl)benzene (1.0 g, 2.3 mmol) in THF (20 ml) at 78 C was added a pentane solution of t-buli (1.4 M, 9.8 ml, 13 mmol). The resulting mixture was stirred at the same temperature for 15 min, and then gradually warmed to room temperature. Selenium powder (0.36 g, 4.6 mmol) was then added in one portion, and the mixture was stirred for 15 min. Addition of water (40 ml) precipitated a yellow solid, which was collected by filtration, washed successively with water, methanol, and ether, and dried (0.77 g, 74%); mp > 300 C; MS (EI) m/z 438 (M + ). Anal. Calcd for C 22 H 14 Se 2 : C, 60.57; H, Found: C, 60.61; H, DPh-BDS was further purified by vacuum sublimation (280 C / 10-3 Pa) for device preparation. Recrystallization from benzonitrile gave thin plate-like crystals suitable for X-ray crystallographic analysis. S2

3 2,6-Dipheny-benzo[1,2-b:4,5-b ]dithiophene (DPh-BDT, 1). The title compound was synthesized as described for DPh-BDS, substituting sulfur powder for selenium powder. DPh-BDT was obtained as a yellow solid in 50 % yield. mp > 300 C; MS (EI) m/z 342 (M + ). Anal. Calcd for C 22 H 14 S 2 : C, 77.15; H, Found: C, 77.23; H, The sample was further purified by vacuum sublimation (270 C / 10-3 Pa) before device preparation. 2,6-Dipheny-benzo[1,2-b:4,5-b ]ditellurophene (DPh-BDTe, 3). To a solution of 1,4-dibromo-2,5-bis(phenylethynyl)benzene (654 mg, 1.5 mmol) in THF (30 ml) at 90 C was added a pentane solution of t-buli (1.5 M, 6.0 ml, 9.0 mmol). The mixture was stirred at the same temperature for 1 h, and then gradually warmed to 0 C. Tellurium powder (383 mg, 3.0 mmol) was added in one portion, and, the mixture was stirred for 15 min at 0 C. To the resulting mixture was added diluted HCl solution (1 M, 50 ml), and the mixture was stirred for 2h at room temperature. A resulting yellow precipitate was collected by filtration, washed successively with water, methanol, and dichloromethane, and dried. The crude solid was extracted by means of a Soxhelt procedure into carbon disulfide, and the extract was concentrated to give yellow solid. Recrystallization from carbon disulfide hexane gave golden fine crystals of DPh-BDTe (0.33 g, 41%); mp > 300 C; MS (EI) m/z 536 (M + ). Anal. Calcd for C 22 H 14 Te 2 : C, 49.52; H, Found: C, 49.49; H, For device preparation, DPh-BDTe was purified by vacuum sublimation (300 C / 10-3 Pa). 2. Device preparation OFETs were fabricated on heavily doped n + -Si (100) wafers with a 230 nm thermally grown SiO 2 (C i =1.50 x 10-8 Fcm -2 ). The organic semiconductor film (50 nm thick) was vacuum deposited onto the Si/SiO 2 substrate, and succeedingly Au films (80 nm) as drain and source electrodes were deposited on the organic layer through a shadow mask. For a typical device, the drain-source S3

4 channel length (L) and width (W) are 50 µm and 1.5 mm, respectively. Characteristics of a drain current (I DS ) versus drain voltage (V DS ) of the OFET devices were measured under vacuum with an ADVANTEST R6245 power supply. The field-effect mobilities (µ FET ) were calculated in the saturation regions of the I ds using the equation I DS = (WC i /2L) µ FET (V G -V T ) 2, where C i is the capacitance of the SiO 2 insulator, V G and V T are the gate and threshold voltages, respectively. 3. XRD patters of 1-3 X-ray diffractions of the organic thin films deposited on Si/SiO 2 substrate were obtained with Maxscience M18XHF diffractometer with a Cu Kα source (λ = 1.541µ) in air. (001) (002) (003) (004) θ / degree sub = rt sub = 60 C sub = 100 C Figure S1. XRD patterns of the evaporated thin films of 1 (T sub = 100 C) 2 (T sub = 60 C), and 3 (T sub = rt). The estimated monolayer thicknesses are d = 17.9 Å (1), 18.0 (2), and 18.5 Å (3), respectively. S4

5 4. AFM images of the evaporated films of 1-3 AFM images of the organic thin films on Si/SiO 2 substrate were obtained by using a Shimadzu SPM-9500 microscope in air. (a) (b) (c) 1 µm 1 µm 1 µm Figure S2. AFM images of the evaporated thin films of 1: (a) T sub = rt, (b) T sub = 60 C, (c) T sub = 100 C. (a) (b) (c) Figure S3. AFM images of the evaporated thin films of 2: (a) T sub = rt, (b) T sub = 60 C, (c) T sub = 100 C. 1 µm 1 µm 1 µm S5

6 (a) (b) (c) Figure S4. AFM images of the evaporated thin films of 3: (a) T sub = rt, (b) T sub = 60 C, (c) T sub = 100 C. 1 µm 1 µm 1 µm 4. References 1 Goldfinger, M. B.; Crawford, K. B.; Swager, T. M. J. Am. Chem. Soc. 1997, 119, Hart, H.; Harada, K.; Du, C.-J. F. J. Org. Chem. 1985, 50, S6