Electron transfer sensitized photolysis of 'onium salts

• Published in: Canadian journal of chemistry Vol. 66; no. 2; pp. 319 - 324
• Main Authors: DeVoe, R. J, Sahyun, M. R. V, Schmidt, Einhard, Serpone, N, Sharma, D. K
• Format: Journal Article
• Language: English
• Published: Ottawa, Canada NRC Research Press 01.02.1988; National Research Council of Canada
• Subjects: Chemistry; Exact sciences and technology; General and physical chemistry; Photochemistry; Physical chemistry of induced reactions (with radiations, particles and ultrasonics); Organic cation; Radical pair; Stationary state; Electron transfer; Singlet state; Pulse photolysis; Quantum yield; Chemically induced dynamic nuclear polarization; Near ultraviolet radiation; Laser beam; Benzenic compound; Rate constant; Photosensitizer
• ISSN: 0008-4042; 1480-3291
• DOI: 10.1139/v88-055

We have studied the anthracene-sensitized photolyses of both diphenyliodonium and triphenylsulphonium salts in solution using both steady-state and laser flash photolysis techniques. Photoproducts, namely, phenylated anthracenes along with iodobenzene or diphenylsulphide, respectively, are obtained from both salts with quantum efficiencies of ca. 0.1 at 375 nm. We infer the intermediacy of diphenyliodo and triphenylsulphur radicals formed by single electron transfer from the singlet-excited anthracene. We have developed a quantitative model of this chemistry, and identify the principal sources of inefficiency as back electron transfer, which occurs at nearly the theoretically limiting rate, intersystem crossing from the initially formed sensitizer-'onium salt encounter complex, and in-cage radical recombination.