Abstract
Excited-state interactions of tris(..cap alpha..-diimine)ruthenium(II) photosensitizers with Hg/sup 2 +/ were studied in aqueous nitrate media by using luminescence quenching and flash photolysis methods. Quenching proceeds via oxidative electron transfer to yield Ru(III) and a Hg(I) free radical with high efficiency. Regardless of the excited-state reducing power of the photosensitizer, quenching was near but below the Marcus diffusion-controlled limit. Dimerization of the Hg(I) free radical to give Hg/sub 2//sup 2 +/ competes effectively with the diffusion-limited back-electron-transfer reaction of the free radical with the Ru(III) species. The back-reaction rate of Hg/sub 2//sup 2 +/ and Ru(III) is much slower and depends on E/sup 0/ (Ru(III/II)). The efficiency of electron-transferred-product separation is sensitive to E/sup 0/ (Ru(III/II)). The mechanism of the oxidation of Hg/sub 2//sup 2 +/ by Ru(III) is discussed.
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