The Electronic Structure of Heteroannelated Cyclooctatetraenes and their UV-Vis Absorption Spectra

The electronic structure and the UV-Vis absorption spectra of heteroannelated cyclooctatetraene derivatives are studied by density functional theory and by its non-stationary variant, the time-dependent density functional theory. The cyclooctatetraene ring is shown to be planar in all of the molecules considered, except the annelated fluorene and dibenzothiophene derivatives, and exhibits an antiaromatic character according to the magnetic and structural aromaticity criteria. The double ionization of annelated cyclooctatetraene molecules (quasi-circulenes) causes a change in the aromatic properties of cyclooctatetraene, which generally gaines aromaticity by double reduction and becomes non-aromatic upon double oxidation. The time-dependent density functional theory calculations enable the interpretation of electronic absorption spectra of recently synthesized quasi-circulenes and to predict the spectra of new, hypothetical molecules, which are important for the general theoretical understanding of hetero[8]circulene spectra.