title: Light-driven tyrosine radical formation in a ruthenium-tyrosine complex attached to nanoparticle TiO2.
abstract: We demonstrate a possibility of multistep electron transfer in a supramolecular complex adsorbed on the surface of nanocrystalline TiO(2). The complex mimics the function of the tyrosine(Z)() and chlorophyll unit P(680) in natural photosystem II (PSII). A ruthenium(II) tris(bipyridyl) complex covalently linked to a L-tyrosine ethyl ester through an amide bond was attached to the surface of nanocrystalline TiO(2) via carboxylic acid groups linked to the bpy ligands. Synthesis and characterization of this complex are described. Excitation (450 nm) of the complex promotes an electron to a metal-to-ligand charge-transfer (MLCT) excited state, from which the electron is injected into TiO(2). The photogeneration of Ru(III) is followed by an intramolecular electron transfer from tyrosine to Ru(III), regenerating the photosensitizer Ru(II) and forming the tyrosyl radical. The tyrosyl radical is formed in less than 5 micros with a yield of 15%. This rather low yield is a result of a fast back electron transfer reaction from the nanocrystalline TiO(2) to the photogenerated Ru(III).
authors.affiliation: Department of Chemical Physics, Lund University, Sweden.
authors.forename: Raed
authors.initials: R
authors.lastname: Ghanem
authors.forename: Yunhua
authors.initials: Y
authors.lastname: Xu
authors.forename: Jie
authors.initials: J
authors.lastname: Pan
authors.forename: Tobias
authors.initials: T
authors.lastname: Hoffmann
authors.forename: Johan
authors.initials: J
authors.lastname: Andersson
authors.forename: Tomás
authors.initials: T
authors.lastname: Polívka
authors.forename: Torbjörn
authors.initials: T
authors.lastname: Pascher
authors.forename: Stenbjörn
authors.initials: S
authors.lastname: Styring
authors.forename: Licheng
authors.initials: L
authors.lastname: Sun
authors.forename: Villy
authors.initials: V
authors.lastname: Sundström