Solvent-polarizability dependence of the relative 2 1Ag(S1)- and 1 1Bu(S2)-fluorescence intensities of 1,14-diphenyl-1,3,5,7,9,11,13-tetradecaheptaene

Emission, excitation, and absorption spectra of diphenyltetradecaheptaene (DP7) have been measured in solvents with different polarizabilities, together with the Raman spectrum at room temperature. DP7 exhibits dual fluorescence from the 2 1Ag(S1) and 1 1Bu(S2) states in room temperature solution. It is shown that the 2 1Ag/1 1Bu fluorescence intensity-ratio varies significantly depending on the solvent polarizability. This observation was interpreted on the basis of the coupling strength between the 2 1Ag/1 1Bu states which is determined mainly by the 2 1Ag–1 1Bu energy separation. Fitting of the spectra with sum of Gaussians reveals a significant difference in Franck–Condon envelop between the 2 1Ag and 1 1Bu fluorescence spectra, which is originating from the large difference in the C–C and C[Double Bond]C stretching mode displacements between the 2 1Ag and 1 1Bu states