PHOTOPHYSICS OF 7-DIETHYLAMINO-4-METHYLCOUMARIN - PICOSECOND TIME-RESOLVED ABSORPTION AND AMPLIFIED EMISSION STUDY

Picosecond time-resolved pump-probe excited state absorption measurements (with a 400-700 nm window) were used to investigate the conformationally sensitive excited charge transfer state of the 7-diethylamino-4-methylcoumarin (C1) laser dye in moderately polar to polar solvents. Time-dependent spectral changes due to amplified (probe beam) emission (AE) were observed in the short wavelength region of our window, together with excited state absorption (ESA) at longer wavelengths. These time-dependent changes are consistent with a single excited state species. Since the transient ESA spectrum of C1 is similar to that of the "rigid" C102 aminocoumarin in aqueous solution and to that of C1 in less polar solvents, the transient is assigned to an excited internal charge transfer (ICT) state rather than to a twisted internal charge transfer (TICT) state of C1. These results do not appear to support previous evidence for the formation of a TICT-solvent exciplex in moderately polar to polar solvents. © 1990.