The influence of thienyl-S,S-dioxidation on the photoluminescence and charge transport properties of dithienothiophenes: a theoretical study

Fused thiophenes have been an important class of materials due to their intriguing organic optoelectronic application. Here, comparative theoretical investigation on the fluorescence and charge transport properties of dithienothiophene compounds (1 and 2) and their dioxide derivatives (3 and 4) was carried out to shed light on the role of the thienyl-S,S-dioxide unit. The lower HOMO, LUMO energy levels, and red-shift spectra (absorption and emission) of 3 and 4 compared with 1 and 2 were attributed to the electron-withdrawing nature of the thienyl-S,S-dioxide unit. The phenomenon that fluorescence quantum yield of 4 was significantly increased through thienyl-S,S-dioxidation, compared with those of 1 and 2, was analyzed by the evaluations of the radiative decay rates and the radiationless decay rates in theory at the single molecule level and the simulation of absorption spectrum of dimer of 1. For 1, a much higher hole mobility (0.12 cm(2)/V.s) calculated by carrier hopping model than the experimental value similar to 10(-4) cm(2)/V.s was also further elucidated by molecular dynamics simulation. Furthermore, a preliminary investigation of the transport property of 3 was performed by combining the molecular dynamics simulation with dispersion-corrected B3LYP functional to provide insight into the effect of thienyl-S,S-dioxidation on the charge transport.