’’Proximity effect’’ in radiationless transitions

Abstract

The quantum statistical approach to relaxation phenomena was employed in a numerical investigation of the effect of vibronic interaction between the first and second excited states on the radiationless decay rate of the first excited state. It is shown that the vibronically active out-of-plane modes may be the dominant accepting modes for the radiationless transitions of N-heterocyclics with close-lying nπ* and ππ* excited states. The decay rate was found to vary with the strength of nπ*–ππ* vibronic interaction, the nπ* and ππ* separation, the energy gap between the initial and final electronic states of the radiationless process, and isotopic substitution, in a manner which is consistent with experimental observation.