PARAMETRIC METHOD FOR CALCULATING THE VIBRONIC SPECTRA OF COMPLEX-MOLECULES - DIPHENYLPOLYENES

The absorption and fluorescence spectra of diphenylpolyenes (diphenylb utadiene, diphenylhexatriene, diphenyloctatetraene, and 1,6-di(4'-meth ylphenyl)-1,3,5-hexatriene) are calculated by a recently proposed para metric method using the fragmentation approach for designing molecular models. The parameters of the (H)>C= molecular fragment (derivatives of the Coulamb and resonance integrals with respect to internal coordi nates in the HAO basis set) obtained in calculations for polyenes were transferred to the molecular models of diphenylpolyenes without chang es (partial derivative H-e/partial derivative q((0)) = 0.055 au and pa rtial derivative(2)H(e)/partial derivative q(k)((0))partial derivative q(l)((0)) = 0.1 au). The theoretical spectra are sufficiently adequat e to quantitatively and qualitatively reproduce the main features of t he vibrational structure of the experimental absorption and fluorescen ce spectra, and the parameters of the models of the potential surfaces of the excited states of diphenylpolyenes are consistent with the pre vious estimations. It is shown that this method allows predictive calc ulations of the vibronic spectra of complex molecules and the develope d parametrization possesses all needed properties: locality, transfera bility, invariance to minor changes in electron density, ranking accor ding to magnitude, small number of parameters for molecular fragments, etc.