Natural and experimental fluorescence lifetimes of benzene in various solvents

Using a nanosecond flash lifetime apparatus the fluorescence lifetime of benzene was determined in a series of polar and nonpolar solvents (including light and heavy water) in the temperature range 6-48° and compared with calculated natural lifetimes. The apparent energy of activation of the nonradiative rate constant k_nr, leading to a decrease of fluorescence with increasing temperature, E_a ∼ 5.3 kcal/mol, is largely independent of solvent, while k_nr itself is solvent dependent. The results are discussed also in relation to the photochemistry of benzene in polar and apolar solvents.