Liquid crystalline dithienothiophene derivatives for organic electronics

Abstract

The synthesis and mesophase characterization of two 2,6-bis(4-(alkyloxy)phenyl)dithieno [3,2-b:2′,2′-d]thiophenes indicate successful application of a palladium-catalyzed carbon-sulfur cross-coupling/5-endo-dig cyclization sequence and the appearance of a nematic mesophase in the resulting products. Spectroscopic and cyclovoltammetric measurements reveal molecular orbital energies that are comparable to a good standard hole conductor. Consequently, one of the compounds was successfully applied as a hole conducting layer in an electroluminescent sample. In thin-film transistors (TFT), the two compounds show charge carrier mobilities in the saturation region μsat of 0.13 cm2V−1s−1 and 0.03 cm2V−1s−1, respectively. The injection barrier at the metal semiconductor interface could be reduced by alkanethiol treatment, thereby enabling a linear ID (VD) characteristics in the low VD region and maximum currents up to ID,max = - 18 μA at VG = - 2.5 V in the saturation regime. Inverter circuits in single-type TFT technology were implemented.