Competition between the nonadiabatic electronic state-mixing and the Herzberg-Teller vibronic effects in fluorescence process of tetraoxa[8]circulene

Abstract

The effect of the nonadiabatic electronic state-mixing between the S1 and S2 states in tetraoxa[8]circulene is investigated computationally. The calculations show that the nonadiabatic electronic state-mixing effect on the fluorescence of tetraoxa[8]circulene is one million times weaker than the Herzberg-Teller vibronic effect. Analysis of the promotive modes of the S0 → S1 and S1 → S0 transitions shows that they are same for both absorption and emission. Also, the Duschinsky effect is found to be very weak for the S0 → S1 and S1 → S0 transitions. The Jahn–Teller symmetry breaking of the S2 state leads to an energy splitting of ~1500 cm−1 between the two components of the S2 state.