title: Synthesis and characterization of dinuclear ruthenium complexes covalently linked to Ru(II) tris-bipyridine: an approach to mimics of the donor side of photosystem II.
abstract: To mimic the electron-donor side of photosystem II (PSII), three trinuclear ruthenium complexes (2, 2a, 2b) were synthesized. In these complexes, a mixed-valent dinuclear Ru2(II,III) moiety with one phenoxy and two acetato bridges is covalently linked to a Ru(II) tris-bipyridine photosensitizer. The properties and photoinduced electron/energy transfer of these complexes were studied. The results show that the Ru2(II,III) moieties in the complexes readily undergo reversible one-electron reduction and one-electron oxidation to give the Ru2(II,III) and Ru2(III,III) states, respectively. This could allow for photooxidation of the sensitizer part with an external acceptor and subsequent electron transfer from the dinuclear ruthenium moiety to regenerate the sensitizer. However, all trinuclear ruthenium complexes have a very short excited-state lifetime, in the range of a few nanoseconds to less than 100 ps. Studies by femtosecond time-resolved techniques suggest that a mixture of intramolecular energy and electron transfer between the dinuclear ruthenium moiety and the excited [Ru(bpy)3]2+ photosensitizer is responsible for the short lifetimes. This problem is overcome by anchoring the complexes with ester- or carboxyl-substituted bipyridine ligands (2a, 2b) to nanocrystalline TiO2, and the desired electron transfer from the excited state of the [Ru(bpy)3]2+ moiety to the conduction band of TiO2 followed by intramolecular electron transfer from the dinuclear Ru2(II,III) moiety to photogenerated Ru(III) was observed. The resulting long-lived Ru2(III,III) state decays on the millisecond timescale.
authors.affiliation: Department of Organic Chemistry, Arrhenius Laboratories, Stockholm University, 106 91 Stockholm, Sweden.
authors.forename: Yunhua
authors.initials: Y
authors.lastname: Xu
authors.forename: Gerriet
authors.initials: G
authors.lastname: Eilers
authors.forename: Magnus
authors.initials: M
authors.lastname: Borgström
authors.forename: Jingxi
authors.initials: J
authors.lastname: Pan
authors.forename: Maria
authors.initials: M
authors.lastname: Abrahamsson
authors.forename: Ann
authors.initials: A
authors.lastname: Magnuson
authors.forename: Reiner
authors.initials: R
authors.lastname: Lomoth
authors.forename: Jonas
authors.initials: J
authors.lastname: Bergquist
authors.forename: Tomás
authors.initials: T
authors.lastname: Polívka
authors.forename: Licheng
authors.initials: L
authors.lastname: Sun
authors.forename: Villy
authors.initials: V
authors.lastname: Sundström
authors.forename: Stenbjörn
authors.initials: S
authors.lastname: Styring
authors.forename: Leif
authors.initials: L
authors.lastname: Hammarström
authors.forename: Björn
authors.initials: B
authors.lastname: Akermark
mesh_terms: D015082:2,2'-Dipyridyl / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry; D056831:Coordination Complexes; D007700:Kinetics; D018716:Molecular Mimicry; D045332:Photosystem II Protein Complex / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D013056:Spectrophotometry, Ultraviolet; D017975:Ruthenium Compounds
chemical_list: D015082:2,2'-Dipyridyl; D056831:Coordination Complexes; D045332:Photosystem II Protein Complex; C547232:tris(2,2-bipyridine)-ruthenium(II); D017975:Ruthenium Compounds