π-Conjugated dithieno[3,2-b:2′,3′-d]pyrrole (DTP) oligomers for organic thin-film transistors

Abstract

Two new molecules with acceptor–donor–donor–acceptor (A–D–D–A) configuration bearing coplanar electron-donating dithieno[3,2-b:2′,3′-d]pyrrole (DTP) as the donor unit and the electron-withdrawing dicyanovinylene as the acceptor block, DTP-L and DTP-S, were synthesized. The introduction of two branched alkyl chains with different lengths at the N-position of DTP led to different transport properties with the longer alkyl chains (DTP-L) showing hole mobility of up to 0.12 cm² V⁻¹ s⁻¹ with on/off ratios of 10⁶ without being subjected to annealing, and the one with short alkyl chains (DTP-S) exhibiting very poor hole mobility of 7.0 × 10⁻⁴ cm² V⁻¹ s⁻¹. The poor performance of DTP-S films was mainly caused by a less ordered film and low crystallinity.