[Electronic structure and energetics of transitions in absorption spectra of hypericin]

In half-empirical sigma, pi-valent approximation (PM3) the energetics of tautomer transitions of hypericin and nature of electronic transitions in experimental and calculation absorption spectra is investigated. On the basis of quantum-chemical researches results concerning five tautomer condition of hypericin is established that the most stable is its known structure of a quinone I (7,14-dion-1,3,4,6,8,13-hexahydroxydianthrone). Is determined that longwave characteristic bands in hypericin experimental absorption electronic spectra are connected with its electron- and proton-donor, and acceptor properties, and are caused by modifications of its quinone structure by formation of alcohols, cation- and anion-radicals.