Temperature and solvent effects on the fluorescence of some simple aromatic molecules

Abstract

The fluorescence yields and lifetimes of α-methylnaphthalene, o-xylene and tetralin in ethanol and methylcyclohexane, toluene in methylcyclohexane, benzene in cyclohexane, methylcyclohexane and ethanol have been measured as a function of temperature, and also for benzene in methanol and acetonitrile at room temperature. In every case, the measured fluorescence yield and lifetime decrease with temperature and are dependent on the solvent used. Expressing the radiative lifetime, τ_r, as τ_r=τ^°_r/n², where n is the refractive index of the medium, it has been found that τ^°_r is constant with temperature for α-methylnaphthalene, o-xylene, tetralin, and toluene. It decreases slightly with increasing temperature for benzene. In every compound the value for τ^°_r, at room temperature, is independent of the solvent used. Possible reasons for the variation of the fluorescence yields with solvent and temperature are discussed. In benzene, solvent perturbations can increase non-radiative disappearance of the S₁ state.