Journal of Organic Chemistry

Photo-CIDNP and Nanosecond Laser Flash Photolysis Studies on the Photodecomposition of Triarylsulfonium Salts

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The direct and sensitized photodecomposition of triarylsulfonium salts have been investigated by nanosecond laser flash photolysis and steady-state photo-CIDNP. The direct photoreaction of triphenylsulfonium salts was shown to proceed via a singlet diphenylsulfinyl radical cation-phenyl radical pair which is produced by internal electron transfer from the initially formed phenyl cation-diphenyl sulfide pair. Recombination of both sets of intermediates gives protonated (phenylthio)biphenyls, identified as a broad transient absorption centered at 465 nm, which lose H+ to give 2-, 3-, and 4-(phenylthio)biphenyl. The acetone-sensitized photoreaction gave a triplet excited state of the salt, which then dissociated to give the triplet diphenylsulfinyl radical cation (λmax 750, 340 nm)-phenyl radical pair and subsequently underwent escape reactions with the solvent. Anthracene-, 9,10-diphenylanthracene-, naphthalene-, and perylene-sensitized photoreactions of triphenylsulfonium salts proceeded by electron transfer from the singlet excited state of the aromatic hydrocarbon to give the singlet aromatic hydrocarbon radical cation-triphenylsulfur radical pair, which dissociates to the in-cage triad of diphenyl sulfide, phenyl radical, and the aromatic hydrocarbon radical cation. In the solvent cage naphthalene radical cation can oxidize diphenyl sulfide to diphenylsulfinyl radical cation, identified by transient absorptions at 750 and 340 nm, whereas the other hydrocarbon radical cations cannot. In contrast to the triphenylsulfonium salts, the [(phenylthio)phenyl]diphenylsulfonium salt decomposed via the triplet excited state upon both direct and triplet-sensitized photolysis. Photo-CIDNP gave a strong enhanced absorption which was quenched upon the addition of oxygen and also gave transients, identified as diphenlsulfinyl radical cation (λmax 750,340 nm), upon both direct and triplet-sensitized photolysis. © 1992, American Chemical Society. All rights reserved.