High-Mobility Regioisomeric Thieno[f,f′]bis[1]benzothiophenes: Remarkable Effect of Syn/Anti Thiophene Configuration on Optoelectronic Properties, Self-Organization, and Charge-Transport Functions in Organic Transistors

π-Conjugated thienoacene-based organic semiconductors with high charge carrier mobility and processability have been intensively pursued for electronic device applications, including organic field-effect transistors (OFETs). Their charge carrier mobility is an important figure of merit, and is influenced not only by the intrinsic electronic structure at molecular level, but also by the molecular packing arrangement and crystallinity in the solid state. In this work, the focus is on a unique regioisomeric thienoacene system involving dialkyl-thieno[f,f′]bis[1]benzothiophene isomers having different syn/anti thiophene configurations (syn- and anti-TBBT-8). The effects of these regioisomeric structures on the physicochemical properties, self-organization behavior, and charge-transport functions are systematically investigated using experimental and theoretical analyses. The structural analyses indicate that the syn- and anti-TBBT-8 isomers self-organize into completely different packing arrangements, in the form of solution-crystallized microribbons and thin films. The resulting charge-transport properties are strongly dependent on the syn/anti thiophene configurations. Remarkably, solution-processed OFETs using the syn-TBBT-8 isomer show high hole mobilities of up to 10.1 cm² V⁻¹ s⁻¹, which are more than one order of magnitude higher than those of the anti-TBBT-8 isomer. This work highlights the importance of the regioisomeric molecular configuration of thienoacene-based organic semiconductors for developing high-performance electronic devices.