Parametric method for computing the structure of the excited states and the vibronic spectra of complex molecules. Absorption and fluorescence spectra of perylene

The structures of the perylene molecule in the first excited 1(1)B(2u) stat e and the band shape (vibrational structure) of its fluorescence and absorp tion spectra are computed by the parametric method. A fragmentary approach and the molecular fragments (H) > C = with the parameters obtained for acen es and polyenes are used to form molecular models ire the excited state. It is shown that a model that corresponds to the choice of fragments with the parameters of acenes is the most optimal. The theoretical spectra satisfac torily reproduce both qualitatively and quantitatively, the basic specific features of the vibrational structure of the experimental spectra. calculat ion results show high degree of transfer of the parameters of the method in a series of related molecules not only for acenes with "linear" arrangemen t of the rings (benzene, naphthalene, anthracene, etc.) but also for more c omplex structures (perylene). It is shown that the parametric method develo ped is efficient for predicting the vibronic spectra and the structure of t he excited states of complex molecules.