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

- Vibronic structure of the electronic absorption spectra for the series of heteroannelated octatetraenes has been studied.
- Both Franck-Condon and Herzberg-Teller approaches have been taken into account.
- All the promotive modes have been determined.
- The structural changes have been analyzed upon the S0 → S1 electronic transition.

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.