Photophysical Processes in the Gas Phase at High Levels of Vibrational Excitation of Triplet Molecules of Benzophenone and Fluorenone

Abstract

By the delayed fluorescence activated by direct multiphoton excitation of triplet molecules by CO2–laser radiation we have studied the prevailing deactivation pathways of triplet molecules with a high store of vibrational energy Evib. The dependences of the kinetic characteristics of delayed fluorescence on the presence of vapors and foreign gases have been used to estimate the rates and efficiencies of intermolecular vibrational relaxation in the vibrational quasi–continuum of the triplet state T1. By the changes in the intensities and decay rates over a wide range of vibrational energies we have established the Evib dependences of reversible intercombination conversion between the states T1 and S1 and interconversion from T1 to the ground electronic state S0 for both the case of “isolated” excited molecules and at a steady vibrational temperature. It is shown that at high vibrational temperatures the radiationless transition from the T1 state to S0 has an activation character and is accomplished through the energy barrier. The conditions for going to an exponential dependence have been determined. It has been found that the obtained dependences are in good agreement with the known experimental results. The influence of molecular and environmental characteristics on the decay rate of triplet molecules is compared.