Medium effects on the fluorescence spectra of tertiary aliphatic amines in mixed solvents and supercritical fluids

Emission spectra of some tertiary amines were measured in cyclohexane (CH)–tetrahydrofuran (THF) mixtures and in supercritical fluids of CHF3. The emission bands of these amines were found to show large successive red shifts with increasing concentration of polar solvent molecules. This finding was rationalized by considering the consecutive solvation of the polar molecules around the Rydberg excited state of the amine. In order to estimate the degree of solvation, the wavenumbers of the emission maxima were plotted as functions of the THF and CHF3 concentrations. The changes in solvation number with increasing THF and CHF3 concentrations were obtained from the spectral shifts by applying a calculation for the stepwise solvation model.