Modulation of electronic structures of thienylene vinylene oligomers by substituents and solvents: ground and excited states

摘要

The effects of substituents on the electronic structures of di(thienylene vinylene) (2TV) in ground and excited states are studied using density functional theory (DFT) and time-dependent DFT (TD-DIFT), respectively. A representative set of electron donating groups (amino, methoxy and methyl) and withdrawing groups (acetylene, cyano and nitro) are introduced on the vinylene and thienyl moieties to investigate the influence of substituents. Bulk solvent effects are also taken into account by means of the polarizable continuum model (PCM). In contrast to the aromatic structures of 2TV and its derivatives in their ground (SO) states, the electronic structures of first singlet excited (S-1) states are rather delocalized. The electron-donating/withdrawing capability, position and number of substituents are important factors in tuning the vertical S-0 -> S-1 absorption energies and S-1 -> S-0 emission energies of 2TV derivatives. The NO2- and NH2-substituents exert significant effects on the geometries of both ground and excited states and hence the absorption and photoluminescence (PL) emission spectra. The solvent polarity introduces modest influence on the excitation energies for most of the 2TV derivatives. But the absorption and PL emission spectra of nitro-substituted 2TV exhibit noticeable red shifts as the medium polarity increases.