Trapping and Damping of Molecular Exciton States

In this paper we show that for an exciton mode coupled to a vibronic state of an impurity or to a different electronic final state of a host molecule (through an intersystem crossing or internal conversion) where the final state is damped, the damping causes a broadening of the initial exciton mode. The damping is considered in terms of Senitzky's theory of the damped quantum oscillator for molecular vibrations and in terms of his theory of the damped two‐level system for the molecular electronic states. The damping constants found in the Senitzky‐type damping theory are related to Green functions. Thus, it is possible to relate the exciton linewidth (or lifetime) to well‐defined energy conversion processes within a molecule. The final energy‐loss step—to the thermal bath—can still be treated by means of an arbitrary damping constant.