Time-resolved vibrational spectroscopy of the degenerate excited singlet states of diphenylhexatriene

Summary form only given.In DPH the relaxation of the initially formed 1/sup 1/B/sub u/ state to a 1/sup 1/B/sub u//2/sup 1/A/sub g/ equilibrium mixture as well as the kinetics of the transients investigated by picosecond time-resolved absorption and fluorescence spectroscopy is still the subject of controversy. We applied picosecond time-resolved resonance coherent antiStokes Raman (CARS) spectroscopy for: (i) characterization of the origin of the transient absorption by the signature of vibrational spectra, (ii) information about the molecular structures of excited electronic states as well as their kinetics, (iii) measurements of the excited state electronic third-order hyperpolarizabilities.