FRANCK-CONDON MODELING OF THE STRUCTURE OF THE 1A(G)-1B(U) ELECTRONIC-TRANSITION OF ALPHA,OMEGA DIPHENYLPOLYENES

The Franck-Condon structure of the lowest lying intense electronic transition, 1A(g)-1B(u), of diphenylbutadiene, diphenylhexatriene, and diphenyloctatetraene is investigated through model calculations. Because of the. relatively low resolution of the spectra available and to avoid a possible bias in the simulation, the Franck-Condon parameters are calculated ab initio through a simple and general approach that can be applied to fairly large molecules. A transferable scaling procedure is used to improve the agreement between computational theory and experiment. The calculated 1A(g)-1B(u) vibroelectronic spectra of the three molecules agree well with the experiment. The modeling allows a better insight into the effects of the one-electron dipole allowed excitation in alpha,omega diphenylpolyenes which are found to differ from pure polyenes of the same chain length in the low-frequency region.