Fluoro-alkyl Substituted Isothianaphthene Bisimides as Stable n-Type Semiconductors

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 type of non-classical thiophenes, possesses 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 alkyl-chains caused different molecular packing style of the resulting materials, as revealed by the atomic force microscope. The crystallinity of BTDI-OCF3 is found to be much better than BTDI-CF and the 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 the glovebox and a 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.