Extended mechanism of excimer formation

Abstract

A modified excimer formation mechanism using an encounter complex, in which the main reaction takes place, is presented and the rate coefficients of the elementary reaction steps are discussed. The kinetic description by ordinary rate equations fails in the case of excimer formation with a time-dependent rate coefficient caused by non-stationary diffusion. Convolution kinetics remain valid in that case and provide decay curves and quantum yields.

Classical and the modified excimer formation mechanisms were investigated to obtain some information about the influence of the molecular kinetic parameters (molecular dimensions, temperature, solvent viscosity). The difference between the rate equation treatment and convolution kinetics becomes smaller when the modified mechanism of excimer formation is used. The influence of temperature on the ratio of excimer to monomer quantum yields shows interesting effects; over a temperature range of 40 K the classical excimer formation mechanism increases by a factor of two, but the modified mechanism increases by a factor of ten.

The slope of measured decay curves are in better accordance with the calculated curves of the modified mechanism and the strong increase of the ratio of excimer to monomer quantum yield can be verified experimentally.