On the role of local vibrational modes in excimer formation

A model recently used to study solid-state excimer formation is generalized to account for the possibility that the strong excited state interactions characteristic of excimers may render the excimer bond less stiff relative to the ground state, complicating the exciton-phonon interaction by introducing a vibrational defect at the location of the excimer. We analyze the changes wrought by such a restructuring of host vibrations. Fits of experimental data from α-perylene suggest a significant softening of the excimer bond; the quality of fit is significantly improved relative to previous work. In the physically interesting regime, excimer state structure is found to be dominated by coupling to the local mode.