SELECTIVITY OF VIBRONIC COUPLING IN COMPLEX-MOLECULES WITH BENZENE FRAGMENTS

This paper deals with the mechanisms of localization of Franck-Condon vibronic coupling of pi pi- or pi l pi*-orbital type in a few vibrati onal modes (LVM) in et-cited electronic stares of polyatomic molecules . The analysis of vibronic coupling uses highly symmetric basis sets ( for representing MO structures and normal coordinates xi(R)) as well a s simplified models that relate the shifts Delta(R) of the electron po tential minima along the normal coordinates to the MO structure and to xi(R) in the form of analytical expressions. The modes that are activ e in LVM are determined from the experimental luminescence spectra. Th ese ideas about approximately high local symmetry of vibronic coupling in benzene fragments as well as the estimates of Delta(R) depending o n variations in the MO structure explain the experimental results.