Isothianaphthene diimide: an air-stable n-type semiconductor

Herein, we propose a new strategy to develop air-stable n-type organic semiconductors with non-classical thiophene aromatic diimide derivatives by replacing aromatic naphthalene with a heteroaromatic isothianaphthene core. We designed and successfully synthesized the isothianaphthene core based diimide material, N,N′-bis(n-hexyl)isothianaphthene-2,3,6,7-tetra-carboxylic acid diimide (BTDI-C6) as an n-type semiconductor. Compared to N,N′-bis(n-hexyl)naphthalene-1,4,5,8-tetracarboxylic acid diimide (NDI-C6), BTDI-C6 possesses a deeper LUMO energy level of −4.21 eV, which is 0.32 eV lower than that of NDI-C6. Both molecular modelling and experimental results elucidated that organic thin film transistors (OTFTs) based on both of these materials exhibit comparable mobilities; however, the threshold voltage of BTDI-C6 based device (+7.5 V) is significantly lower than that of NDI-C6 based counterpart (+34 V). Moreover, the low-lying LUMO energy level of BTDI-C6 ensures excellent air-stability which is further validated by the device performance. In addition, BTDI-C6 shows high luminescence while NDI-C6 is not luminescent at all in solution, which reveals the potential application of our newly synthesized material in n-type light-emitting transistors.