Excitation Energy-Dependent Transient Spectral Relaxation of Coumarin 153

Abstract
We report on the excitation energy-dependent transient spectral response of the polar dye molecule coumarin 153 (C153) in selected solvents. We find that the blue edge of the spontaneous emission spectrum of C153 contains several spectral features and that the relative contribution of these features to the overall response varies with the identity of the solvent and the excitation wavelength. The central result of these data is that the transient spectral response of C153 depends sensitively on the excitation wavelength and that the spectral evolution behavior of this molecule is therefore not related in a simple manner to solvent reorganization dynamics.