Excited state dynamics of guaiazulene using laser-saturated fluorescence

Abstract

We report the results of a laser-saturated fluorescence study of the S2←S0 000 vibronic bands of two conformers of guaiazulene in a supersonic jet. Photophysical parameters were derived from the saturation study using a three-state kinetic model which explicitly accounted for heterogeneous broadening. Since heterogeneous broadening (rotational and Doppler) is significant in heavy polyatomics, this method could become important in extending the utility of saturation studies beyond the atomic and diatomic systems to which the technique has usually been applied. To assess the utility of our kinetic model, we compared the results to those obtained with another commonly used kinetic model which ignores all frequency dependence in a spectroscopic resonance. We also collected direct absorption and unsaturated fluorescence excitation spectra in the jet, and extensive laser beam diagnostics, to parametrize the kinetic model and to provide an independent determination of the absorption cross section. The kinetic fit yielded cross sections around 3 Å2 for the transitions, in good agreement with the direct absorption measurement, and excited-state lifetimes of 760±230 ps, in reasonable agreement with literature values from condensed-phase experiments.