Fluorescence spectra and the 21Ag level of 1,4-diphenylbutadiene in perfluorohexane and perfluoropentane

Fluorescence spectra of diphenylbutadiene (DPB) have been investigated in different environments at room temperature. It is indicated that in perfluorohexane and perfluoropentane the 21Ag state of DPB is located at energies slightly lower than the 11Bu state. Solvent polarizability has been estimated that achieves the inversion of the 21Ag and 11Bu levels. The change of the fluorescence spectral shape upon varying the 21Ag−11Bu energy separation is discussed.