Highly π-extended small molecules with bis(alkylthio)methylene side chains for organic field-effect transistors

Abstract

Organic field-effect transistor (OFET) performance is strongly dependent on not only the conjugated core structure but also the organic semiconductor side chains. This paper reports on indacenodithiophene (IDT) based conjugated small molecules with rarely investigated side chains of bis(alkylthio)methylene as dimethyloctyl (SMOIC) and ethylhexyl (SEHIC) structures for OFET active layers. Basic properties of materials, such as band gap, HOMO and LUMO energy levels, and film crystallinity were similar regardless of the alkylthio side chain structure. SMOIC and SEHIC both exhibited reliable ambipolar charge transport with reasonably high hole (0.052 and 0.148 cm² V⁻¹ s⁻¹) and electron mobilities (0.020 and 0.023 cm² V⁻¹ s⁻¹). Higher hole mobilities were observed in OFETs based on SEHIC with the bis(ethylhexylthio)methylene side chain due to better thin film crystallinity and larger molecular planarity.