Photophysics of a bridged 7-diethylamino-4-methyl-coumarin C102: Studying the hydrogen bonding effect by time resolved stimulated emission

The time-resolved stimulated emission of a 7-diethylamino-4-methyl-coumarin dye, Coumarin 102 (C102), was investigated in polar and hydroxylic solvents. Analysis of these spectroscopic measurements using semiempirical solvent polarity scales (E-T(30), Kamlet and Taft) showed that the stabilization of the excited singlet state is mainly governed by dipolar and hydrogen bonding interactions. This particuliar behavior was reflected by a good adequacy between the present measured solvation times and the microscopic (or molecular) relaxation times related to both the Debye relaxation time To (dielectric continuum model) and the Kirkwood factor g(k), which expresse the degree of short range order in the liquid. These data were compared with the ones obtained for thioxanthone via pump-probe experiments and other data available in the literature.