Estimation of the bimolecular rate constant for exciplex formation from the analysis of its emission spectrum

The bimolecular rate constant for the quenching of l-methylnaphthalene by triethylamine was measured in series of solvents covering a large range of solvent polarity (epsilon = 2-37). The formation of a fluorescent exciplex was observed in all the solvents studied. Analyzing the emission of the exciplex, it is possible to estimate the relevant parameters associated with the radiative back electron transfer process, namely, the solvent dependent Gibbs energy change, the solvent reorganization energy, and the internal reorganization energy. These parameters are used to calculate, according to Marcus theory, the rate constant for the photoinduced forward electron transfer reaction. A good correlation between calculated and experimental quenching rate constants is observed.