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High‐Performance Air‐Stable Single‐Crystal Organic Nanowires Based on a New Indolocarbazole Derivative for Field‐Effect Transistors

2013; Volume: 25; Issue: 24 Linguagem: Inglês

10.1002/adma.201300740

1521-4095

Kyung Park, Sonali M. Salunkhe, Iseul Lim, Cheon‐Gyu Cho, Sung‐Hwan Han, Myung M. Sung,

Advanced Memory and Neural Computing

A new indolocabazole derivative possessing an extended aromatic core and solubilizing long aliphatic chains effectively self-assembles and crystallizes within the nanoscale channels to form single-crystal nanowires via a direct printing method from an ink solution. Single-crystal organic nanowire transistor arrays based on the π-extended indolocarbazole derivative exhibit an excellent hole mobility of 1.5 cm2 V−1 s−1 and outstanding environmental stability. Organic semiconductors are cheap to produce and can be flexibly shaped and simply printed on plastic substrates. Owing to their processability advantages and unique optoelectrical properties, organic semiconductors have recently attracted significant interest in large-area, low-cost, light-weight, and flexible electronics.1 In other words, they have great potential for applications as active elements in flexible optoelectronic devices such as organic light emitting diodes, photovoltaic cells, and field effect transistors.2 In particular, the organic field-effect transistor (OFET) is a fundamental building block for organic electronics, including identification tags, smart cards, solar cells, sensors, and flexible displays.3 Organic semiconductors in OFETs can be divided into two categories, small molecules and polymers.2 Typical examples of p-type semiconducting small molecules are pentacene, tetracene, rubrene, and their derivatives, and some examples of semiconducting polymers are poly(3-hexylthiophene) and poly(p-phenylene vinylene). Among them, pentacene is one of the most promising p-type organic semiconductors and has exhibited excellent mobility in OFETs, but it requires vapor phase deposition which is a critical obstacle in reducing the manufacturing costs for organic electronics.4 Thus, a functionalized pentacene, 6,13-bis(triisopropylsilylethynyl) (TIPS) pentacene, was developed as a promising semiconducting molecule for high performance solution processed OFETs.5 TIPS-pentacene has sufficient solubility in common organic solvents and high mobility. However, pentacene and its derivatives have relatively high-lying highest occupied molecular orbital (HOMO) energy levels and narrow band gaps, which make them susceptible to air-oxidation, resulting in degraded semiconducting performance when processed in air or operated under ambient conditions.6 These drawbacks make this class of compounds less practical for further applications. Indolocarbazole (ICZ) and its derivatives have been also studied as a promising class of semiconductors for OFETs because of their rigid, linear, coplanar conjugated structures without active centers for Diels-Alder reactions.7 ICZ and its derivatives have good p-channel semiconducting properties and the addition of side chains on their nitrogen atoms enhances solubility in common organic solvents. Furthermore, these molecules have shown significantly improved environmental stability due to low-lying HOMO energy levels and larger band gaps compared with pentacene and its derivatives.7, 8 However, the ICZ derivatives still have the drawback of low charge mobility.7, 7, 8, 9 The properties of charge transport in molecular materials are strongly related to the presence of delocalized π-electrons. From these considerations, it should be possible to extend the π-conjugated system while ensuring air-stability, or retaining low-lying HOMO energy levels. In the search for highly conductive systems, new ICZ molecules with a large π-orbital area in their aromatic cores are currently being investigated.7, 7, 8, 10 In ICZ derivatives, environmental stability is usually maintained, while extension of the conjugation translates in an increased self-assembly tendency, resulting in self-organized structures and consequently to an increased charge mobility. Herein, we report the synthesis of a new ICZ derivative, 8,16-didodecyl-8,16-dihydrobenzo[a]benzo[6,7]indolo[2,3-h]carbazole (C12-BBICZ), and demonstrate its application in OFETs as an organic semiconductor. This molecule has a rigid, linear, coplanar conjugated structure with a large π-orbital area in the aromatic core and alkyl side chains on its nitrogen atoms. C12-BBICZ has good solubility in common organic solvents and easily crystallizes to form single-crystal nanowire arrays via a direct printing method, liquid-bridge-mediated nanotransfer molding (LB-nTM) method.11 The C12-BBICZ-based single-crystal nanowire FETs exhibit an excellent hole mobility of 1.5 cm2 V−1 s−1, which is the highest value reported with ICZ and its derivatives. In addition, they have good environmental stability even with prolonged operation under ambient conditions. The brief scheme for synthesis of C12-BBICZ is shown in Scheme 1 (see the detail procedure in Scheme S1 in the Supporting Information). Two long pendant alkyl groups on the nitrogen atoms are positioned in the molecular long-axis direction of the core and thus facilitate lateral intermolecular interaction. C12-BBICZ indeed turned out quite soluble in common organic solvents, as summarized in Table S1 in the Supporting Information. The solubilities of several BBICZ derivatives bearing various pendant N-alkyl groups (C5 through C16) were also investigated; their solubilities increased in proportion to the increase of the alkyl chain length up to C12, while the further increase to C16 diminished the solubility. Cyclic voltammetry measurements were carried out to investigate the redox potentials of C12-BBICZ. The HOMO energy level estimated from its oxidation potential is about -5.32 eV below the vacuum level, as shown in Figure S1 in the Supporting Information. The UV–vis absorption edge in Figure S2 in the Supporting Information shows that the band gap of C12-BBICZ is about 2.9 eV. The relatively deep HOMO energy level and large band gap in comparison with TIPS-pentacene apparently facilitate its good stability in air.6 Schematic procedure for synthesis of 8,16-didodecyl-8,16-dihydrobenzo[a]benzo[6,7]indolo[2,3-h]carbazole (C12-BBICZ). Recently, we developed a new direct printing method, liquid-bridge-mediated nanotransfer molding (LB-nTM) method.11 This simple method enables the simultaneous synthesis, alignment, and controlled positioning of single-crystal organic nanowires on substrates from molecular ink solutions. The C12-BBICZ molecules in the ink solution self-assemble and crystallize within the nanoscale channels of molds to form single-crystal nanowires, which are directly transferred to specific positions on the substrate via a liquid bridge to generate nanowire arrays, as shown in Figure 1a. Scanning electron microscopy (SEM) images of C12-BBICZ nanowire arrays fabricated using a mold (110 nm parallel lines and 90 nm spaces) clearly show that the nanowires, each with a width of 90 nm and a height of 140 nm are perfectly aligned to form 200 nm period arrays on the substrates (Figure 1b). This procedure can be used to generate single-crystal C12-BBICZ nanowire arrays with controlled orientations and alignments on flexible substrates. Printed single-crystal C12-BBICZ nanowire arrays can be used in OFETs for transparent, flexible, inexpensive, and large-area applications. Fabrication of single-crystal C12-BBICZ nanowire arrays. a) A schematic of the procedure used to fabricate single-crystal C12-BBICZ nanowire arrays on substrates using LB-nTM. The C12-BBICZ ink solution that fills the nanoscale recessed channels of the mold solidifies after drying and is then placed in contact with the substrate covered by a thin ethanol layer. After drying, the separation of the mold from the substrate yields single-crystal C12-BBICZ nanowire arrays. b) SEM images of the C12-BBICZ nanowire arrays (white) fabricated by LB-nTM on Si substrates (black). Inset: magnified view of the nanowire arrays at the corresponding perspective (the nanowire width, W, is 90 nm; the spacing between nanowires, S, is 110 nm; and the nanowire height, H, is 140 nm). The molecular orientation and crystal structure of the C12-BBICZ nanowire arrays were determined by selective-area electron diffraction (SAED) and X-ray diffraction (XRD). Figure 2a shows the transmission electron microscopy (TEM) image and corresponding SAED patterns obtained perpendicular to the length axis of a C12-BBICZ nanowire. The SAED patterns recorded from the three different regions along the C12-BBICZ nanowire exclusively exhibit reflections of the monoclinic structure oriented along the [010] zone axis, indicating that it is of a single-crystalline nature. The molecular orientation of the nanowire arrays was confirmed by the XRD pattern of the C12-BBICZ nanowire arrays on the Si substrate. XRD was performed in reflection mode such that the scattering vector was perpendicular to the substrate (i.e., parallel to the nanowire axis). The XRD pattern (Figure 2b) shows a well-defined set of (0k0) reflections, which indicates that the b axis of the C12-BBICZ nanowire is oriented parallel to the surface normal with its ac plane on the substrate (Figure 2d). For the analysis of the crystal structure, the lattices unit cell modeling and corresponding electron diffraction simulations in commercial software packages (Single Cryatal 2.2.5. Crystal Maker Software Ltd.) were utilized. These results indicate that the C12-BBICZ nanowire has a monoclinic crystal structure with cell dimensions of a = 5.03 Å, b = 13.7 Å, c = 15.6 Å, and β = 105°, and forms in the nanochannels of the molds along the [100] direction, which coincides with the π–π stacking direction. Ideally, C12-BBICZ should have strong interactions with neighboring molecules to maximize the overlap of π molecular orbits and thus facilitate the efficient charge transport for high field-effect mobility. Crystal structures of C12-BBICZ nanowires. a) TEM image of the C12-BBICZ nanowire and the corresponding SAED patterns in different areas. Each area shows a single-crystalline nature. b) XRD patterns of the C12-BBICZ nanowire arrays fabricated on the Si substrate by LB-nTM. c) TEM image of a C12-BBICZ microribbon and the corresponding SAED pattern, which indicates its semicrystalline nature. d) Schematic representation of the crystal structure of a single-crystal C12-BBICZ nanowire along the nanowire direction. For comparison, C12-BBICZ microribbons were fabricated by LB-nTM using a micro-patterned mold with 3 μm parallel lines and 2 μm spaces. The TEM image and corresponding SAED patterns for the C12-BBICZ microribbon are shown in Figure 2c. Many discrete diffraction spots in each Debye ring indicate that the microribbon has preferred-oriented semicrystalline ordering. This result could be attributed to the crystallization of C12-BBICZ in the nanochannels of the molds during the LB-nTM process. In the LB-nTM process, the self-assembly processess are affected by the scale of the channel width and thus, the crystallization in confined nanochannels results in a preferential alignment of a specific direction with respect to the mold.12 It can therefore be concluded that the nanoconfinement effect provided by the nanochannels in the molds is crucial for the formation of the single-crystal C12-BBICZ nanowires using this method. Organic single crystals usually show intrinsic charge-transport properties and the highest performance due to the perfect order of molecules, the absence of grain boundaries, good contact interfaces, and a minimal number of charge traps.13 We fabricated large-scale arrays of FETs on 5 × 5 cm2 polyethersulfone (PES) substrates by LB-nTM using single-crystal C12-BBICZ nanowires as active channels. A 150 nm-thick indium tin oxide (ITO) gate electrode and a 200 nm-thick SiO2 dielectric layer were formed on a PES substrate by sputter deposition. Then, ten C12-BBICZ nanowires that served as active channels were fabricated on each FET device by LB-nTM. Finally, source and drain electrodes of 1.5 μm-thick Ag were defined to contact the C12-BBICZ nanowires on the device by LB-nTM (Figure 3a). Note that the channel width and length were 900 nm and 5.5 μm, respectively. The channel width is determined from the single nanowire width multiplied by the number of nanowires in the channel. C12-BBICZ nanowire FETs. a) Photograph of an array of single-crystal C12-BBICZ nanowire FETs on a flexible substrate (left). SEM images of a typical nanowire FET where the Ag source-drain electrodes were defined by a subsequent LB-nTM (right, top). The SEM image shows the well-aligned nanowire array channel between the Ag electrodes (right, bottom). b) Drain current–drain voltage (IDS–VDS) output curves obtained from the FETs with ten C12-BBICZ nanowires. c) Drain current–gate voltage (IDS–VGS) transfer curves (VDS = –50 V) of the same device. d) The environmental stability of a single-crystal nanowire FETs under ambient conditions. Figure 3b shows typical source-drain current versus source-drain voltage (IDS–VDS) curves measured at various gate voltages (VG) for the FETs with ten C12-BBICZ nanowires in the channel region. It is evident that the IDS increases with VDS for a given VG, and that the conductance increases drastically with negative VG, indicating that this device is a p-channel FET. Figure 3c is the corresponding source-drain current versus source-gate voltage (IDS–VGS) transfer curve at VDS = –50 V. An on/off current ratio of about 105 is obtained. From the intersection point of the exponential and nonexponential regions of the transfer curve, the threshold voltage (Vth) can be determined to be about -4.7 V. The field effect mobility of the C12-BBICZ nanowire FET was estimated to be about 1.5 cm2 V−1 s−1. Field effect mobility from over twenty individual devices reveals an average mobility of 1.5 cm2 V−1 s−1 with the highest up to 1.8 cm2 V−1 s−1. C12-BBICZ FETs with from 1 to 20 single-crystal nanowires were fabricated in a similar manner using LB-nTM. The FET characters were well modulated by the number of the nanowires in the channels, as shown in Figure S3 in the Supporting Information. The transfer characteristics of the single-crystal C12-BBICZ nanowire FETs before and after bending (bending direction across the channel) are also presented in Figure 3c. No significant loss in performance was observed when the devices were bent to a radius as small as 6 mm, as found in bending experiments performed on five randomly chosen devices that all exhibited similar behavior. This performance is comparable to that of field effect transistors containing TIPS-pentacene single crystals.14 We also monitored the field-effect mobility of the single-crystal C12-BBICZ nanowire FETs with exposure time in air under controlled relative humidity and temperature (Figure 3d). Our experiments were carried out in an environmental chamber, where relative humidity (±2%) and temperature (±1 °C) could be controlled simultaneously. Relative humidity and temperature were kept fixed in all experiments at 50% and 20 °C, respectively. After 30 days, the single-crystal C12-BBICZ nanowire FETs still operated with constant field effect mobility, indicating that the device exhibited outstanding environmental stability. These results indicate that the single-crystal C12-BBICZ nanowire FETs are therefore useful for flexible organic electronics with excellent environmental stability. In conclusion, we have successfully developed a π-extended indolocarbazole derivative, C12-BBICZ, as a new organic semiconductor with high mobility and stability. The C12-BBICZ molecules possessing an extended aromatic core and solubilizing long aliphatic chains effectively self-assemble and crystallize within the nanoscale channels to form single-crystal nanowires via a direct printing method from the ink solution. The highly extended π-framework that contributes to strong intermolecular interactions has been found to improve greatly its molecular ordering in the nanowires, resulting in high carrier mobility. We believe that the printed single-crystal C12-BBICZ nanowire arrays could be used in flexible electronics as a stable p-type active channel for high-performance OFETs. Synthesis: Unless otherwise stated, reactions were performed under an argon atmosphere using freshly dried solvents. Tetrahydrofuran, dichloromethane, toluene, and ethyl ether were dried by passing them through activated alumina columns. Methanol and benzene were dried over activated molecular sieves and distilled. Degassing was carried out by the standard freeze-pumping-thaw cycle. All other commercially obtained reagents were used as received. All reactions were monitored by thin-layer chromatography using EMD/Merck silica gel 60 F254 pre-coated plates (0.25 mm). The TLC spots were visualized under a UV lamp or using staining solutions such as ceric ammonium molybdate solution, p-anisaldehyde or potassium permanganate solution. Flash column chromatography was performed with the indicated solvents using silica gel (GS60–40/75) purchased from Fuji Silysia Chemical. 1H NMR and 13C spectra were recorded at 400 MHz (Varian Mercury 400 MHz) or 600 MHz (Varian VNMRS 600 MHz). Chemical shifts are reported relative to tetramethylsilane (0 ppm), internal chloroform (1H, δ = 7.26 ppm, 13C, δ = 77.1 ppm), or DMSO (1H, δ = 2.50 ppm, 13C, δ = 39.5 ppm). Infrared spectra were recorded on an ABB FTLA2000 FTIR spectrometer. High resolution mass spectra were measured using the FAB method. Dibenzyl 5,6,13,14-tetrahydrobenzo[a]benzo[6,7]indolo[2,3-h]carbazole-8,16-dicarboxylate 5: To a flask containing acetonitrile (30 mL) and a few drops of conc. H2SO4 were added dibenzyl 1,1′-(1,4-phenylene)bis(hydrazinecarboxylate) 3 (500 mg, 1.2 mmol) andaα-tetralone (396 mg, 2.7 mmol) at room temperature (RT). The reaction mixture was heated under reflux until all starting material was consumed, as judged by TLC. After completion, the reaction mixture was cooled down to RT and filtered off. The solid product collected on a funnel was thoroughly washed with acetonitrile and dried to give a mixture of 5 and 5′ (3:1) in the combined yield of 90%. FTIR (KBr): 3128, 2312, 1729, 1387, 1222, 1156 cm−1; HRMS (FAB) calculated for C42H32N2O4 (M+) 628.2357, found 628.2363. Dibenzyl benzo[a]benzo[6,7]indolo[2,3-h]carbazole-8,16-dicarboxylate 6: To a suspension of 5 and 5′ (597 mg, 0.9 mmol) in benzene (50 mL) was added DDQ (1.22 g, 5.7 mmol) at RT. The resulting mixture was stirred for one day at RT. After the completion of the reaction, the reaction mixture was concentrated in vacuo and added to K2CO3 (791 mg, 5.7 mmol), methanol (30 mL) and distilled H2O (10 mL). The mixture was then heated at 60 °C for 30 min. The reaction mixture was cooled down to RT, filtered off, oven-dried and recrystallized from EtOAc to give 6 as yellow solids. 1H NMR (DMSO-d6, δ): 8.76 (s, 2H), 8.29 (d, J = 8.4 Hz, 2H), 8.06 (dd, J = 8.0, 7.2 Hz, 4H), 7.62 (d, J = 7.2 Hz, 4H), 7.52 (m, 5H), 7.42 (m, 5H), 5.67 (s, 4H); FT-IR (KBr): 3129, 1738, 1400, 1164 cm−1; HRMS (FAB) calculated for C42H28N2O4 (M+) 624.2044, found 624.2051. 8,16-Dihydrobenzo[a]benzo[6,7]indolo[2,3-h]carbazole 7: To a suspension of 6 (100 mg, 0.16 mmol) in tetrahydrofuran (THF) was added 1 M tetra-n-butylammonium fluoride (TBAF) in THF (0.8 mL, 0.8 mmol) at RT. The reaction mixture was heated under reflux. After 8 h, the reaction mixture was cooled to RT and quenched by adding 1 M aqueous HCl. The resulting yellow slurry was filtered off, washed with EtOAc and distilled H2O, and dried to give 7 (48 mg) in 80% yield. 1H NMR (DMSO-d6, δ): 12.00 (bs, 2H), 8.56 (d, J = 8.0 Hz, 2H), 8.36 (d, J = 8.4 Hz, 2H), 8.32 (s, 2H), 8.04 (d, J = 8.4 Hz, 2H), 7.62 (t, J = 7.4 Hz, 2H), 7.53 (t, J = 7.4 Hz, 2H); 13C NMR (DMSO-d6, δ): 136.6, 134.9, 131.9, 128.5, 125.1, 125.0, 122.9, 122.0, 121.1, 119.7, 118.1, 117.3, 100.2; HRMS (FAB) calcd for C26H16N2 (M+) 356.1308, found 356.1311. 8,16-Didodecyl-8,16-dihydrobenzo[a]benzo[6,7]indolo[2,3-h]carbazole 8: To a well stirred mixture of 7 (100 mg, 0.28 mmol), benzyltriethylammonium chloride (13 mg, 0.06 mmol), 1-bromododecane (279 mg, 1.12 mmol) and DMSO (4 mL) was added freshly prepared 50% aqueous NaOH solution (0.56 mL) at RT. The mixture was stirred at RT for 3 h and heated at 65 °C. After 4 h, the reaction mixture was cooled down to RT and poured into a beaker containing methanol (40 mL) while being stirred. The precipitated yellow solids were filtered off, washed successively with water, methanol and acetone and dried to furnish 9 (178 mg) in 92% yield. 1H NMR (CDCl3, δ): 8.52 (d, J = 8.8 Hz, 2H), 8.32 (d, J = 8.4 Hz, 2H), 8.16 (s, 2H), 8.05 (d, J = 8.0 Hz, 2H), 7.67 (d, J = 8.8 Hz, 2H), 7.59 (t, J = 7.4 Hz, 2H), 7.51 (t, J = 7.0 Hz, 2H), 4.84 (t, J = 7.6 Hz, 4H), 2.12 (pent, J = 7.2 Hz, 4H), 1.60 (pent, J = 6.8 Hz, 4H), 1.44 (pent, J = 6.8 Hz, 4H), 1.25 (m, 28H), 0.85 (t, J = 6.4 Hz, 6H); 13C NMR (CDCl3, δ): 137.0, 135.8, 133.7, 129.5, 125.1, 124.4, 122.6, 122.2, 122.0, 119.6, 119.1, 97.8, 46.3, 31.9, 29.8, 29.7, 29.6, 29.4, 29.3, 27.1; FTIR (KBr) 2920, 2850, 1501, 1463, 1375, 1252, 1112, 794 cm−1; HRMS (FAB) calcd for C50H64N2 (M+) 692.5064, found 692.5070. Preparation of Substrates: The Si substrates used in this research were cut from n-type (100) wafers with resistivity in the range of 1–5 Ω cm. The Si substrates were initially treated to remove contaminants by the chemical cleaning process proposed by Ishizaka and Shiraki, which involves degreasing, HNO3 boiling, NH4OH boiling (alkali treatment), HCl boiling (acid treatment), rinsing in deionized water, and blow-drying with nitrogen.15 A thin oxide layer was grown by placing the Si substrate in a piranha solution (4:1 mixture of H2SO4:H2O2) for 10–15 min. The substrate was rinsed several times in deionized water (resistivity = 18 MΩ cm), and was then dried with a stream of nitrogen. The flexible substrates employed in this study were cut from Glastic polyethersulfone (PES) films (i-Components Inc.). The PES substrates were cleaned with methanol and de-ionized water, and were blow-dried with nitrogen to remove contaminants. Growth of Single-Crystal C12-BBICZ Nanowires: Single-crystal C12-BBICZ nanowire arrays were made on an oxidized Si(100) or PES substrate using the LB-nTM method with polyurethane acrylate (PUA) (MINS-ERM, Minuta Tech.) molds. The masters used for the fabrication of the molds were silicon wafers with dense nanoscale line patterns, which were made by e-beam lithography. The molds were fabricated by casting PUA on them. After UV curing (≈10 min), the PUA molds were peeled away from the masters. The C12-BBICZ ink solution was prepared by dissolving it in 1,3,5-trichlorobenzene (TCB) (99%, Sigma Aldrich Inc.). To generate the arrays of single-crystal C12-BBICZ nanowires, only the recessed channels of the patterned PUA mold were filled with the C12-BBICZ ink solution using discontinuous dewetting.11, 16 By dragging a deposited ink solution over the patterned mold with a glass stick or a needle, the meniscus of the ink solution moved over the surface of the mold to fill the nano-diameter channels without leaving any residue on the raised surface. The ink in the nanoscale channels was next solidified by drying at mild temperatures below 100 °C for 30–60 min. During solidification, the C12-BBICZ molecules in the ink solution self-assembled and crystallized to form single-crystal nanowires within the nanoscale channels. The mold with the single-crystal C12-BBICZ nanowires was then brought into contact with a substrate surface covered by a thin ethanol layer. A substrate of area 1 cm × 1 cm was uniformly covered with a 100 μm-thick ethanol layer by using ethanol (10 μL). The ethanol layer on the substrate formed a liquid bridge (a capillary bridge) between the substrate and the mold that contained the single-crystal organic nanowires in channel patterns. The liquid bridge allowed good conformal contact between the nanowires and the substrate. As the ethanol evaporated, the attractive capillary force gradually increased, pulling the two surfaces into contact, and providing good conformal contact between them with no additional pressure on the mold. After drying, the separation of the mold from the substrate yielded single-crystal organic nanowire arrays. Micrometer scale Ag electrodes were fabricated on the PES substrates using LB-nTM with a polydimethylsiloxane (PDMS) (Sylgard 184, Dow Corning) mold. The masters used for the PDMS mold fabrication were silicon wafers with patterned resists on scales from 5 to 100 μm, which were made by photolithography. The molds were fabricated by casting PDMS on the masters. After being cured at 70 °C for 50 min, the PDMS molds were peeled away from the masters. The PDMS molds were then filled with Ag solution (20 wt% in methanol, particle diameter 40–50 nm, DGP 40LT-15C). The solidified Ag electrodes in the molds were also transferred to specific positions of the PES substrate with pre-patterned single-crystal organic nanowires by liquid-bridge-mediated transfer. Characterization: 1H NMR and 13C spectra were recorded at 400 MHz (Varian Mercury 400 MHz) or 600 MHz (Varian VNMRS 600 MHz). Chemical shifts are reported relative to tetramethylsilane (0 ppm) or internal chloroform (1H, δ = 7.26 ppm, 13C, δ = 77.1 ppm) as indicated. Infrared spectra were recorded on an ABB FTLA2000 FTIR spectrometer. UV–vis spectra were recorded on a Hewlett-Packard 8452A diode array spectrophotometer. The redox properties of C12-BBICZ were monitored by cyclic voltammetry (BAS 100B, Bioanalytical Systems, Inc.). Electrochemical measurements were performed using a single compartment with a Pt wire as a counter electrode, an Ag/AgCl reference electrode and a 0.1 M tetra(n-butyl) ammonium tetrafluoroborate (TBATFB) in acetonitrile solution as electrolyte. The organic nanowires were characterized using a scanning electron microscope (SEM, Hitachi S4800) operated at 15 kV. The crystallinity of the organic nanowires was determined by a selective-area electron diffraction (EM 912 Omega) with a transmission electron microscope run at 120 kV and confirmed by X-ray diffraction (XRD) (Bruker D8) using a Cu source run at 40 kV and 40 mA. The current–voltage (I–V) properties of the FETs were measured with a semiconductor parameter analyzer (HP 4155C, Agilent Technologies) in the dark and in ambient air (relative humidity ≈ 45%) at 20 °C. The field-effect mobility (μ) and threshold voltage (Vth) were calculated in the saturation regime (VDS = -50 V) by plotting the square root of the drain current versus the gate voltage using IDS = (WCi/2L)μ(VGS − Vth)2, where Ci is the capacitance/unit area of the gate dielectric layer, and W and L are the channel width and length, respectively. Supporting Information is available from the Wiley Online Library or from the author. This work was supported by the National Research Foundation (NRF) grant funded by the Korea government (MEST) (No. 2012-0008678), and the Global Frontier R&D Program on the Center for Multiscale Energy System (No. 2011-0031562), Nano•Material Technology Development Program (2012M3A7B4034985), and a Global Ph. D. Fellowship Program (No. 2011-0007507) funded by the National Research Foundation under the Ministry of Science, ICT & Future, Korea. We thank the Korea Basic Science Institute (KBSI) for allowing us to use their EF-TEM. 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