Tyrosine groups enhance photoinduced intramolecular electron transfer in polypyridyl ruthenium(II) complexes

The complexes [cis-RuII L ′ 2 (SCN)2 and cis-RuIILL′(SCN)2] (L = 4,4′-bis(ethoxycarbonyl)-2,2′-bipyridine, L′ = 2,2′-bpy-4,4′-CONH-l-tyrosine ethyl ester) are prepared and characterized. Two or four tyrosine ethyl ester groups are covalently linked to a ruthenium polypyridyl photosensitizer as electron donor. Upon light excitation, intermolecular electron transfer from the excited ruthenium(II) to MV2+ occurs, followed by intramolecular electron transfer from tyrosine moieties to Ru(III) with a rate constant of kf > 1 × 108 s−1 (τf < 10 ns).