Synthesis and characterization of carbazole- and α-carboline-based thiophene derivatives as organic semiconductors for organic thin-film transistors

New thiophene derivatives, end-functionalized with carbazoles (9-(5-(9H-carbazol-9-yl)thiophen-2-yl)-9H-carbazole), carbazole and a-carboline (9-(5-(9H-carbazol-9-yl)thiophen-2-yl)-9H-pyrido[2,3-b]indole), and alpha-carbolines (9-(5-(9H-pyrido[2,3-b]indol-9-yl)thiophen-2-yl)-9H-pyrido[2,3-b] indole) were synthesized and characterized as organic semiconductors for organic thin-film transistors (OTFTs). The best device performance was achieved via a hexamethyldisilazane dielectric surface treatment of thermally grown Si-SiO2 substrates prior to vapor-phase semiconductor deposition. Within this family, the semiconductor having an electron-donating (carbazole) and an electron-withdrawing (alpha-carboline) substituent exhibited the highest p-channel characteristic with a carrier mobility as high as 0.014 cm(2) V-1 s(-1) and a current on/off ratio of 7 x 10(5) for top-contact/bottom-gate OTFT devices. The device characteristics have been correlated with the film morphologies and microstructures of the corresponding compounds. (C) 2014 Elsevier Ltd. All rights reserved.