Fluoro-alkyl substituted isothianaphthene bisimides as stable n-type semiconductors

Abstract

The development of air-stable organic semiconductors (OSCs) with high charge mobilities is of pivotal importance for practical applications of organic thin film transistors (OTFTs) in various fields. Although several OSCs with high hole mobilities have been realized, their n-type counterparts lag far behind in terms of charge mobilities and especially air-stability potentially due to the highly sensitive nature of electrons to ambient oxidants. Isothianaphthene, a kind of non-classical thiophene, possesses a unique electronic structure and isothianaphthene bismide (BTDI) has been demonstrated as an efficient core for stable n-type OSCs. In this work, we introduced two fluoric groups with different alkyl-chains at the N-position of isothianaphthene-2,3,6,7-tetracarboxylic acid diimide and obtained new air-stable n-type OSCs, BTDI-OCF₃ and BTDI-CF. The distinct length of the alkyl-chains caused different molecular packing styles of the resulting materials, as revealed by atomic force microscopy. The crystallinity of BTDI-OCF₃ is found to be much better than BTDI-CF and single crystals of BTDI-OCF₃ could easily be obtained by solution process. Besides, OTFTs based on these new semiconductors showed almost no hysteresis when tested in a glovebox and very small hysteresis is observed in air with a small decay of current, indicating good stability of both of these materials for their applications in n-type OTFTs.