Supporting Information for Pyromellitic Diimide Ethynylene Based Homopolymer Film as an N-Channel Organic Field-Effect Transistor Semiconductor Srinivas Kola, Joo Hyun Kim, Robert Ireland, Mingling Yeh, Kelly Smith, Wenmin Guo and Howard E. Katz* Department of Materials Science and Engineering and Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States Department of Polymer Engineering, Pukyong National University, Yongdang-Dong, Nam-Gu, Busan 608-739, Korea Experimental General Reagents were purchased from Aldrich Inc. and Acros Organics (NJ, USA) and used without further purification unless otherwise stated. 2-(4-trifluoromethylphenyl)ethyl amine and 3,6-dibromopyromellitic dianhydride were prepared by following the reported procedures. 1-3 Column chromatography was conducted with silica gel 60 (400 mesh). 1 H NMR spectra were recorded on Bruker Avance (300 MHz/400 MHz) spectrometers. Absorption spectra were acquired using a spectrophotometer (Cary 50 UV/vis). DSC measurements were carried out using a TA DSC Q20 modulated instrument at a heating rate of 10 C/min and a cooling rate of 10 C/min under a nitrogen atmosphere. The polymer film was dip coated on the platinum wire and then used for CV acquisition. The electrochemical measurements were carried out in acetonitrile solutions under N 2 with 0.1 M tetrabutylammonium hexafluorophosphate (NBu 4 PF 6 ) as the supporting electrolyte at room temperature using an Autolab PGSTAT 302
potentiostat/galvanostat. The cyclic voltammograms were obtained at a scan rate of 100 mv/s. A platinum disk and platinum wire were used as the working and counter electrodes, respectively, and Ag/Ag + (0.01M AgNO 3 ) was used as the reference electrode. Synthesis and Characterization N,N -Di-n-octyl-3,6-dibromopyromellitic Diimide (1): To a solution of 3,6-dibromopyromellitic dianhydride (2Br-PyDA) (0.8 g, 2.13 mmol) in dry THF (90 ml) was added a solution of n- octylamine (0.83 g, 6.40 mmol) at room temperature under nitrogen and the mixture was stirred overnight. The solvent was removed under reduced pressure to give the amic acid. Anhydrous sodium acetate (0.70 g, 8.52 mmol) and 30 ml acetic anhydride were added to the amic acid, and the mixture was stirred under nitrogen for 3 h at 100 o C. The reaction mixture was poured into cold water, and the precipitate was collected by filtration and purified by column chromatography eluting with dichloromethane to give the desired compound in 60% yield (0.76 g) as a white powder: 1 H-NMR (400MHz, CDCl 3 ) 3.72 (t, 4H), 1.70 (m, 4H), 1.33 (m, 20H), 0.88 (m, 6H). N,N -Di-(2-(4-trifluoromethylphenyl)ethyl)-3,6-dibromopyromellitic Diimide (2): Compound 2 was prepared by following the above procedure using 2-(4-trifluoromethylphenyl)ethyl amine and 2BrPyDA. Pale yellow powder. 1 H-NMR (400MHz, CDCl 3 ) 7.57 (d, 4H), 7.37 (d, 4H), 3.98 (t, 4H), 3.07 (t, 4H). Polymer P1: 1 (1g, 1.7 mmol) and bis(tributylstannyl)acetylene (1.028g, 1.7 mmol) were dissolved in 35 ml of anhydrous toluene and de-aerated by bubbling with nitrogen gas for 15 minutes and then tetrakis(triphenylphosphine)palladium (59mg, 0.051mmol) was added at once
and the reaction mixture refluxed under nitrogen for 3 days. The reaction mixture was allowed to attain room temperature and then the homogeneous polymer solution was poured slowly into 200 ml of methanol under vigorous stirring. After stirring for 1 h, the precipitate was filtered through a Buchner funnel. The dissolution and precipitation processes were carried out three times and finally the precipitate was transferred to a thimble for Soxhlet extraction. Sequential Soxhlet extraction was carried out with methanol, acetone and hexane solvents to remove oligomers. After extraction with chloroform, the polymer solution was concentrated and reprecipitated in methanol to afford 120 mg of olive green solid. No significant insoluble fraction remained after the chloroform extraction. Yield = 16%, M n =3.8 kda, PDI=1.76. 1 H-NMR (400MHz, CDCl 3 ) 3.71 (br, 4H), 1.70 (br, 4H), 1.40 1.10 (br, 20H), 0.88 (br, 6H). Polymer P2: P2 was synthesized by following the above procedure using monomer 2 in the place of 1. Mustard color solid. Yield = 80%, Mn=5.9 kda, PDI=1.95. 1 H-NMR (400MHz, CDCl 3 ) 7.8 6.8 (br, assuming 8H), 4.2 3.4 (br, 4H), 3.2 2.6 (br, 4H). Device Fabrication and Characterization All processes other than metal evaporation were carried out under ambient conditions. Heavily n-doped silicon wafers with 300 nm thermally grown SiO 2 dielectric layers were purchased from Process Specialties. Wafers were cleaned using piranha solution (a 3:1 mixture of sulfuric acid and 30% hydrogen peroxide; Caution! piranha solution is extremely corrosive and reactive), deionized water, acetone, and isopropyl alcohol, followed by drying in nitrogen flow. Then gold source/drain electrodes (30 nm) with a thin underlying chromium adhesive layer (3 nm) were patterned by conventional photolithography, thermal evaporation, and lift-off process. The drain and source contacts were interdigitated gold electrodes with channel length of 50 μm and channel width of 8100 μm. P1 polymer was dissolved in chlorobenzene to make
10mg/mL solution. The semiconducting layer was deposited by spin-coating the above solution at 1000 rpm for 60 seconds and then annealed at 150 0 C for 10 minutes in air. After cooling with nitrogen flow, the gate-dielectric layer (CYTOP, thickness~400 nm) was deposited by spincoating a mixture of CYTOP CTL-809M and CT-solv 180 (1:1 ratio) at 1000 rpm for 60 seconds followed by baking at 100 0 C for 15 minutes. The devices were completed by thermal evaporation of patterned Al gate electrodes (100 nm thick) through a shadow mask. Devices were evaluated in vacuum using a Keithley 4200 semiconductor analyzer in an ST-500-1 vacuum triaxial probe station purchased from Janis Research Company, Inc. The mobilities were calculated from the saturation regime and fitted in the regions of highest slope. Thermoelectric samples were prepared by dissolving the polymer in toluene (10 mg/ml) and spin-casting the solution onto glass substrates having prepatterned gold electrodes (10 mm in length with 4 mm between each other, ca. 50 nm thicknesses by thermal evaporation). The substrates were then held at 150 C for 10 minutes. Polymer film thickness was measured to be ~50 nm using Keyence VK-X100 series Laser Microscope 3D. The Seebeck coefficient of pure polymer was measured at room-temperature by four-probe measurement. Two thermocouple probes measure the temperature difference created across the film, achieved by thermoelectric generators, and two probes measure the voltage potential. As the temperature gradient is changed, the plot for ΔV versus ΔT can be constructed, where the slope is the Seebeck coefficient. The measurement was calibrated using Ni metal, for which the value (-21.0 ± 0.6 µv/k) agrees well with those reported (-20.5 µv/k). Conductance was measured using a semiconductor parameter analyzer (compliance set to 10 ma, minimum current reading is <100 pa).
Heat Flow (W/g) 1.5 P1 P2 1.0 0.5 0.0-0.5-1.0 80 120 160 Temperature ( 0 C) Figure S1. DSC thermogram (second cycle) of P1 and P2. Figure S2: Output curves and transfer curves of best performing devices, with P1 as semiconducting layer in TGBC configuration.
Figure S3. Output curves and transfer curves of P1-based FETs at various channel lengths (L=50 µm, 25 µm and 10 µm) in TGBC configuration with fixed channel width of 3000 µm.
Intensity (counts) Figure S4: Output curves of P1-based device (Bottom-Gate Top-contact configuration) 40000 22500 10000 2500 0 4 6 8 10 12 14 16 18 20 22 24 2Theta ( ) Figure S5. XRD spectrum of P1. The peak around 2 = 4 0 is an instrumental or substrate artifact.
Figure S6. 1 H-NMR spectrum of 1.
Figure S7. 1 H-NMR spectrum of 2.
Figure S8. 1 H-NMR spectrum of P1.
Figure S9. 1 H-NMR spectrum of P2. The peaks around alkyl region may be from the terminal tributyltin compound. Similar complications were also observed in other ethynyl-linked polymers. 4
Figure S10. FT-IR spectra of P1 and P2. Weak C C stretching observed in the range of 2000-2250 cm -1, which corresponds to symmetrically substituted alkyne. 4 References: 33. (1) Miller, D. J.; Saunders, J. W. H. J Org Chem 1981, 46, 4247. (2) Guo, X.; Watson, M. D. Macromolecules 2011, 44, 6711. (3) Suh, D. H.; Chung, E. Y.; Hong, Y.-T.; Choi, K.-Y. Die Angew. Makromol. Chem. 1998, 254, (4) Alvey, P. M.; Iverson, B. L. Org. Lett. 2012, 14, 2706.