In this contribution, we report visible light driven Br– oxidation by the metal-to-ligand charge transfer (MLCT) excited states of Ru(deeb)(bpz)22+, (deeb = 4,4’-diethylester-2,2’-bipyridine; bpz = 2,2’-bipyrazine), in acetone. Stern-Volmer analysis of time resolved photoluminescence data yielded KSV = 1.0×105 M–1 and a quenching rate constant close to the diffusional limit, kq = 5.7×1010 M–1s–1. Nanosecond transient absorption spectroscopy was employed to quantify the excited state reaction mechanism and both Ru(deeb)(bpz)2+ and Br2●– were identified as photoproducts. The second-order rate constant for the appearance of Ru(deeb)(bpz)2+ was 5.0±1.0×1010 M–1s–1, which was within experimental error the same as the loss of the MLCT excited state, suggesting that Ru(deeb)(bpz)2+ was a primary photoproduct. The formation rate constant of Br2●– was found to be about a factor of three smaller 1.8×1010 M–1s–1, but similar to the Br●+Br– → Br2●– rate constant that was measured separately. The kinetic analysis indicates bromine atoms as intermediates in the sensitized oxidation of bromide. To our knowledge, this study represents the first report of visible-light driven Br-Br bond formation with a molecular excited state that may be exploited in photo-electrochemical cells and solar fuel generation.

Bromine atom formation by visible light driven bromide oxidation with a Ru polypyridyl compound

249th National Meeting (2015)

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