Biphotonic photochemistry of benzophenones in dimethylsulphoxide: a flash photolysis EPR study |
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| Authors: | JONATHAN R WOODWARD TIEN-SUNG LIN YOSHIO SAKAGUCHI HISAHARU HAYASHI |
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| Institution: | 1. Department of Chemistry , The University of Leicester , University Road, Leicester, LE1 7RH, UK;2. Department of Chemistry , Washington University , Campus Box 1134, One Brookings Drive, St. Louis, MO, 63130-4899, USA;3. The Institute of Physical and Chemical Research (RIKEN) , Wako, Saitama, 351-0198, Japan |
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| Abstract: | Benzophenone and its derivatives in dimethylsulphoxide (DMSO) exhibit biphotonic photochemistry under 355 nm laser photolysis. Flash photolysis electron paramagnetic resonance experiments demonstrate that a single laser pulse is capable of producing and exciting benzophenone triplets, which can sensitize dimethylsulphoxide and subsequently lead to photodecomposition. In decafluorobenzophenone, electron transfer is the dominant process of the highly excited triplet state. Despite the rapid radiationless decay of 2-hydroxybenzophenone (2OHbenzophenone) in non-polar solvents, radical signals are observed from the photoexcitation of 2OHbenzophenone in DMSO. This is attributed to the sufficiently rapid excitation of the triplet state, which competes with the radiationless decay process, aided by the unique solvent properties of DMSO. It is concluded, in contrast to literature data, that the excited triplet state of DMSO is reactive, and can produce methyl radicals that show triplet mechanism polarization via the biphotonic photoexcitation of benzophenone. |
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