Oligothiophene-functionalized benzene and tetrathienoanthracene: Effect of enhanced π-conjugation on optoelectronic properties, self-assembly and device performance

Abstract

The versatility of fourfold Stille coupling to afford oligothiophene- functionalized tetrathienoanthracene (TTA and benzene derivatives is described. The influence of the larger, more rigid TTA core on the electronic and structural properties was investigated. Comparative optical and electrochemical studies demonstrate a diminishing HOMO-LUMO gap as the length of the oligothiophene chain increases, with the rigid TTA compounds exhibiting lower energy gaps than the more flexible benzene analogues. X-ray crystallography studies reveal that the thiophene-substituted TTA structure consists of slipped π-stacks with several close intrastack π-π interactions; no close contacts are observed for the benzene derivative due to twisting of the thiophene ligands out of plane. Consequently, the molecules in the benzene analogue are isolated from their neighbours. The thiophene and bithiophene functionalised TTA compounds were fabricated into OTFT devices in bottom-contact configuration and exhibited mobilities of ca. 10-4 cm2 V-1 s-1 and on/off ratios of more than four orders of magnitude. The tetrathienoanthracene (TTA framework is explored as a star-shaped core that extends π-conjugation in two dimensions. The effect of "expanding" the conjugation by lengthening the oligothiophene side chains is demonstrated with enhanced optoelectronic properties. Compared with its more flexible benzene analogue, the TTA derivatives show smaller band gaps and tight π-stacked structures. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.