Photophysics and photochemistry ofo-xylene solutions I. Radiative processes of the1B1 state

Abstract The radiative decay processes of the excited monomer singlet and excimer states of o -xylene in solution have been examined as functions of temperature and concentration. The fluorescence rate constants for both states are independent of temperature. The values of the enthalpy (0.196 eV) and entropy (−8.8 × 10 −4 eV K −1 of formation of o -xylene excimer are less than for benzene as a result of steric influence of the methyl groups. The ground state repulsion energy (∼ 0.61 eV) is greater than for benzene for similar reasons. The nature of the perturbation due to substituents is briefly discussed.