Excited States of Dicyanovinyl-Substituted Oligothiophenes from Many-Body Green's Functions Theory

Abstract

Excited states of dicyanovinyl-substituted oligothiophenes are studied using many-body Green's functions theory within the GW approximation and the Bethe-Salpeter equation. By varying the number of oligomer repeat units, we investigate the effects of resonant-antiresonant transition coupling, dynamical screening, and molecular conformations on calculated excitations. We find that the full dynamically screened Bethe-Salpeter equation yields absorption and, emission energies in good agreement with experimental data. The effect of resonant-antiresonant coupling on the first singlet pi -> pi* excitation monotonically decreases with increasing size of the molecule, while dynamical screening effects uniformly lower the excitation energies.