Chalcogen substitution: Effect of oxygen-by-sulfur exchange on structural and spectroscopic properties of flavonols

Quantum chemical calculations using density functional theory have revealed that the substitution of the ketone group by a thioketone one doesn't significantly change the structure of 3-hydroxyflavone. Notably, the strong intramolecular hydrogen bond involving the hydroxyl function is preserved if the O atom is substituted by an S atom, but also by Se or Te atoms. However, fundamental modifications are observed in both absorption and emission electronic spectra upon substitution, particularly the non-fluorescent behavior of the flavothione. All these changes were explained by the optimizations of the different excited states carried out by time-dependent DFT method.