Picosecond CARS and transient absorption studies of 1,4-diphenylbutadiene and trans-stilbene: A study of photoinduced formation of a radical cation

We report the direct observation of the formation and stabilization of radical cations of trans-stilbene and 1,4-diphenylbutadiene (DPB) in polar solvents (acetonitrile, linear alcohols) by picosecond ?pump?probe? and polarization sensitive resonant CARS experiments. For the first time we have observed the formation and stabilization rate of the DPB radical cation, which occurs on a 10?20 ps time scale. We confirm that the formation process is mainly monophotonic and depends on the polarity of the solvent but found no correlation between the formation and stabilization rate and the solvent dielectric relaxation time