Alkoxy substituted [1]benzothieno[3,2-b] [1] benzothiophene derivative with improved performance in organic thin film transistors

2-(4-(octyloxy) phenyl)[1] benzothieno[3,2-b][1] benzothiophene (C8-OPh-BTBT), a liquid crystal material, is designed and successfully synthesized by introducing an alkoxy side chain of BTBT core. The organic thin-film transistors (OTFTs) based on C8-OPh-BTBT are fabricated to investigate the charge transport properties and compare with that of the alkyl side chain substituted semiconductor such as C12-Ph-BTBT. The highest mobility of 8.25 cm(2) V-1 s(-1) in C8-OPh-BTBT-based OTFTs is obtained when fabricated at a highly ordered Smectic X (X = K or H, SmX) liquid crystal phase, which is attributed to the formation of a bilayer structure of the organic semiconductor. Notably, the mobility of alkyoxy-substituted C8-OPh-BTBT-based OTFTs is much higher than that of alkyl-substituted C12-Ph-BTBT based OTFTs, while decreasing the operating threshold voltage. This study reveals that the introduction of alkoxy side chain of BTBT core is an effective way to alleviate the high threshold voltage and improve the charge mobility, which indicates that C8-OPh-BTBT-based OTFTs have the potential in practical applications.