Inhomogeneous spectral broadening and the decay kinetics of the luminescence spectra of prodan

The selectively excited steady-state luminescence spectra, as well as the decay time characteristics of the luminescence, of prodan in polar solvents excited by picosecond radiation are studied. The steady-state luminescence spectra exhibit a strong inhomogeneous broadening, which is the most pronounced at elevated solution viscosities. The temporal characteristics of the luminescence decay in different spectral ranges and the instantaneous spectra suggest the presence of relaxation processes resulting in a long-wavelength shift of the emission spectrum during the lifetime of the excited state. A relation between the relaxation shift of the emission spectrum and the intermolecular orientational relaxation of solvate molecules is established.