DFT simulation of the heteroannelated octatetraenes vibronic spectra with the Franck-Condon and Herzberg-Teller approaches including Duschinsky effect

Calculations of vibronic structure in the electronic absorption spectra are carried out for the series of heteroannelated octatetraenes on the basis of density functional theory method. Both Franck-Condon and Herzberg-Teller approaches have been used for estimation of frequency and intensity of vibronic bands in the simulated absorption spectra with respect to the S₀ → S₁ electronic transition. The key result discussed in this work is that the electronic transition into the first singlet excited states is vibronically-active in the absorption spectra for all studied circulenes in a good agreement with experimental observations. We have confirmed our previous assumption that the first (low-lying) weak absorption maximum in the spectra of tetra-tert-butyltetraoxa[8]circulene and dithieno[3,4-b:3′,4′-d]thiophene-annelated cyclooctatetraene can be assigned just for the S₀ → S₁ transition which produce the next more intense vibronic satellite. In the case of aza[8]circulenes the S₀ → S₁ transition is symmetry allowed and the corresponding vibronic bands are less intense relative to 0-0 band.