Parametric method for calculating the vibronic spectra of complex molecules. Diphenylpolyenes

The absorption and fluorescence spectra of diphenylpolyenes (diphenylbutadiene, diphenylhexatriene, diphenyloctatetraene, and 1,6-di(4′-methylphenyl)-1,3,5-hexatriene) are calculated by a recently proposed parametric method using the fragmentation approach for designing molecular models. The parameters of the^H>C=molecular fragment (derivatives of the Coulomb and resonance integrals with respect to internal coordinates in the HAO basis set) obtained in calculation for polyenes were transferred to the molecular models of diphenylpolyenes without changes (∂H_e/∂q⁽⁰⁾=0.055 and ∂²H_e/∂q _k ⁽⁰⁾ ∂q _l ⁽⁰⁾ =0.1 au). The theoretical spectra are sufficiently adequate to quantitatively and qualitatively reproduce the main features of the vibrational structure of the experimental absorption and fluorescence spectra, and the parameters of the models of the potential surfaces of the excited states of diphenylpolyenes are consistent with the previous estimations. It is shown that this method allows predictive calculations of the vibronic spectra of complex molecules and the developed parametrization posesses all needed properties: locality, transferability, invariance to minor changes in electron density, ranking according to magnitude, small number of parameters for molecular fragments, etc. K. A. Timiryazev Moscow Agricultural Academy. Translated fromZhurnal Struktumoi Khimii, Vol. 37, No. 6, pp. 1040–1049, November–December, 1996. Translated by I. Izvekova