Stochastic Model of Molecular Luminescence

Abstract

A general kinetic mechanism for molecular luminescence including vibrational relaxation has been proposed and solved analytically for the case in which the vibrational relaxation is faster than the electronic relaxation and for the case in which the electronic relaxation is faster than the vibrational relaxation. The purpose of this paper has been to investigate the role played by the vibrational relaxation in molecular luminescence and how the vibrational relaxation affects the measurements of the lifetimes of electronic states under various experimental conditions. We have theoretically shown that if the rate of vibrational relaxation is much faster than that of electronic relaxation, the rate constants (radiative and nonradiative) experimentally determined represent the equilibrium microcanonical averaged rate constants or the equilibrium thermal averaged rate constants depending on whether the system is isolated (collision free) or thermal, and if the rate of electronic relaxation is much faster than that of vibrational relaxation, for small molecules the rate constants determined are the rate constants of single vibronic states if the system is selectively excited.