Design of Reactivity of Organic Cation Radicals Generated by Photoinduced Electron Transfer

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The present study deals with the design of reactivity of organic cation radicals generated by photosensitized electron transfer in solution. The sensitizers employed are 2, 4, 6-triphenylpyrylium salt (TPP), 2, 4, 6-triphenylthiapyrylium salt (STPP), and 9, 10-dicyanoanthracene (DCA) 1. Firstly, cation radicals of diarylethanals were generated by TPP, STPP and/or DCA, and the products were compared. Laser flash photolysis has also been carried out to elucidate the reactive intermediates involved. The results suggest that the reacivity of diarylethanal having 4, 4-dimethoxy groups in the presence of oxygen is quite different between DCA and TPP sensitized reactions.2. Secondary, tetrakis (4-methylphenyl) ethanone was investigated with DCA and TPP as sensitizers, and it was found that the C-C bond cleavage occurred in both reactions with different mechanisms for the product formation of same kinds.3. Thirdly, Deprotonation of 9, 10-dihydroanthracene was studied in the presence of oxygen with DCA and TPP sensitization. We have found that TPP sensitized oxygenation gave anthracene whereas DCA sensitization gave anthrone as a primary, major product. The results were interpreted in terms of the acidity of superoxide radical anion (O_2^-.) involved in DCA sensitized oxygenation, which is absent in the TPP sensitized oxygenation. 4. Lastly, TPP and DCA sensitized oxygenation were carried out for stilbene (ST), triphenylethylene (TPE), and tetraphenylethylene (TEPE), and comparison of products revealed that TEPE does not react with molecular oxygen while ST and TPE react. All olefins studied were found to react with O_2^-. The observed difference of reactivity of olefin cation radicals were discussed in terms of stability of intermediate peroxy radical cations and dioxetane cation radicals.