Photochemical reactions of T1 benzopyranthione 3-methylpentane

✍ Scribed by Jan Kozłowski; Andrzej Maciejewski; Marek Milewski; Wojciech Urjasz

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 92 KB
• Volume: 12
• Category: Article
• ISSN: 0894-3230
• DOI: 10.1002/(sici)1099-1395(199901)12:1<47::aid-poc87>3.0.co;2-v

✦ Synopsis

Photochemical properties of the lowest triplet state of 4H-1-benzopyran-4-thione (BPT) in 3methylpentane were studied in the thione concentration range 10 À7 À 10 À3 M. The quantum yield of the photochemical decomposition of BPT was found to be highly concentration dependent. For low BPT concentrations (10 À6 M) a reaction with the solvent is responsible for the consumption of the thione. In the concentration range 1 Â 10 À6 -8 Â 10 À5 M the main process is the reaction of thiyl radicals, formed in the primary reaction of hydrogen abstraction from a solvent molecule, with BPT molecules in the ground state. For thione concentrations b10 À4 M, the BPT triplet decays almost entirely in a self-quenching process. HPLC analysis showed that five different photoproducts, including an oligomer, are formed. Knowledge of earlier studied photophysical properties of BPT in 3-methylpentane and perfluoroalkanes permitted a quantitative explanation of the mechanism of photochemical reactions of 3 (BPT). The studies indicate, for BPT concentrations 10 À4 M, a dominant role of the interaction of 3 (BPT) with the solvent and the subsequent caged radical recombination in deactivation of BPT in the T 1 state.