Understanding the effects of sulfur di-oxidation and side chain engineering on absorption and fluorescence of oligothiophene: A theoretical study

Abstract

Oligothiophene and its derivatives have broad applications in organic electronics because of its stability, easy functionalization, and broad color adjustability, and excellent charge carrier mobility. However, the effects of sulfur di-oxidation and side alkyl chains on the absorption and fluorescence of oligothiophene are still not well understood. In this article, we have applied density functional theory (DFT) and time-dependent DFT (TDDFT) to study a series of quinquethiophene compounds functionalized with S,S-dioxide and side alkyl chains, which were experimentally synthesized. Through benchmark calculations, we have found a reliable computational method, and successfully reproduced experimental UV–Vis absorption and fluorescence emission spectra well. Furthermore, the calculated reorganization energy of these molecules could explain the energy differences between absorption and emission spectra. Last but not lease, we also have calculated the fluorescence quantum yield efficiency (Фfl) of two compounds with good planarity in this series, and the trend of calculated values is consistent with experiment. Our work gives an insight to the effects of sulfur di-oxidation and side chain engineering on absorption and fluorescence of oligothiophene.