New tetrathiafulvalene fused-naphthalene diimides for solution-processible and air-stable p-type and ambipolar organic semiconductors

Abstract

New conjugated electron donor–acceptor molecules with tetrathiafulvalene (TTF) fused-naphthalene diimide frameworks (1–6) are synthesized and investigated. The NDI cores are flanked by TTF and 2-(1,3-dithiol-2-ylidene)malonitrile moieties within 1–3, whereas compounds 4–6 contain two TTF moieties. Based on cyclic voltammetric and absorption spectral studies, the LUMO and HOMO energies of 1–3 are estimated to be ca. −4.3 eV and ca. −5.1 eV, and those of 4–6 are ca. −4.1 eV and ca. −5.0 eV, respectively. These values are consistent with theoretical calculations. Thin films of 1–6 are easily prepared with the spin-coating technique and the resulting OFETs are successfully fabricated with conventional procedures. The OFETs results reveal that compounds 1–3 behave as ambipolar semiconductors and 4–6 as p-type semiconductors. Among 1–3, compound 3 exhibits relatively high hole and electron mobilities in air, reaching 0.03 and 0.003 cm2 V−1 s−1, respectively, after annealing at 160 °C. The OFET based on a thin film of 5 shows the best performance with μh = 0.31 cm2 V−1 s−1, Ion/off = 104 among compounds 4–6 after annealing at 160 °C. The thin films of 1–6 are investigated with XRD and AFM, and the data can well interpret the variation of carrier mobilities of 1–6 after annealing. Moreover, the influences of alkyl chains in 1–6 on the intermolecular arrangements and carrier mobilities are also discussed.