EXCITED-STATE DYNAMICS OF BARRIERLESS ISOMERIZATION IN SOLUTION

Using excited state absorption decay experiments (ESA), time-resolved fluorescence and stimulated emission measurements, we have further investigated the photophysics of the barrierless isomerization of the molecule 1,1'-diethyl-4,4'-cyanine. The observed fluorescence lifetimes are strongly wavelength dependent. The lifetime increases when the fluorescence wavelength is increased. We show how this fluorescence behaviour can explain the wavelength dependence observed in ground state recovery (GSR) experiments presented earlier, where for ''red'' GSR wavelengths (590-630 nm) the influence of fast kinetic components due to stimulated emission is present. The ESA experiments were performed at three different wavelengths (467, 476 and 488 nm) using the technique with continuous analyzing light and up-conversion of the probe signal. The observed excited state life-times are in good agreement with the lifetimes observed in ground state recovery experiments as well as the fluorescence measurements presented here.