Fluorescence spectra of all trans 1,4-diphenylbutadiene obtained by the two-photon excitation into the 21Ag state

The fluorescence spectra obtained by the two-photon excitation into the 21Ag state of diphenylbutadiene (DPB) have been measured in room temperature solutions, along with the one- and two-photon absorption spectra. It is shown that DPB molecule excited into the two-photon allowed 21Ag state through the two-photon process exhibits the fluorescence from the two-photon forbidden 11Bu state irrespective of the solvent polarizability. Relaxation processes followed by the two-photon excitation into the 21Ag state, and the shape of the two-photon absorption spectra measured when the 21Ag origin is located below the 11Bu origin are discussed.