Spectroscopic and photochemical properties of aromatic thioketones: xanthione

D. A. Capitanio, Henry J. Pownall, J. Robert Huber

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Some aspects of the absorption, emission and photochemistry of xanthione (XS), an aromatic thioketone with a C molecular geometry, have been investigated in solution at room temperature and 77 K. Contrary to the observation in similar aromatic ketones, the first Π, Π* transion (1A1 » 1A1) of thioketones has charge-transfer character as indicated by the results of a CNDO/2-CI calculation. The short lived emission observed at room temperature and at 77 K (τp(77 K) = 43 μs; Φp(77 K) = 0.11) is polarized parallel to the CS axis and is assigned as phosphorescence of the lowest 3(n, Π*) state. The exceptionally effective spin-orbit coupling of aromatic thioketones (about two orders of magnitude larger than in the ketone analogs) indicates that a different intersystem crossing mechanism is operative in aromatic thioketones from that of ketones. The photo-oxidation of XS to xanthone proceeds via the lowest n, Π* triplet state of XS. The photodecomposition is most efficient in oxygen-free alcoholic solutions and involves the excited XS molecule and the solvent.

Original languageEnglish (US)
Pages (from-to)225-236
Number of pages12
JournalJournal of Photochemistry
Issue number1
StatePublished - Jan 1 1974


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