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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
Author(s) -
Xu Yunhua,
Eilers Gerriet,
Borgström Magnus,
Pan Jingxi,
Abrahamsson Maria,
Magnuson Ann,
Lomoth Reiner,
Bergquist Jonas,
Polívka Tomáš,
Sun Licheng,
Sundström Villy,
Styring Stenbjörn,
Hammarström Leif,
Åkermark Björn
Publication year - 2005
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200500592
Subject(s) - ruthenium , moiety , chemistry , electron transfer , bipyridine , excited state , crystallography , electron donor , photochemistry , stereochemistry , catalysis , crystal structure , physics , nuclear physics , biochemistry
To mimic the electron‐donor side of photosystem II (PSII), three trinuclear ruthenium complexes ( 2 , 2 a , 2 b ) were synthesized. In these complexes, a mixed‐valent dinuclear ${{\rm Ru}{{{\rm II}{\rm \char44}{\rm III}\hfill \atop 2\hfill}}}$ 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 ${{\rm Ru}{{{\rm II}{\rm \char44}{\rm III}\hfill \atop 2\hfill}}}$ moieties in the complexes readily undergo reversible one‐electron reduction and one‐electron oxidation to give the ${{\rm Ru}{{{\rm II}{\rm \char44}{\rm II}\hfill \atop 2\hfill}}}$ and ${{\rm Ru}{{{\rm III}{\rm \char44}{\rm III}\hfill \atop 2\hfill}}}$ 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 ( 2 a , 2 b ) to nanocrystalline TiO 2 , and the desired electron transfer from the excited state of the [Ru(bpy) 3 ] 2+ moiety to the conduction band of TiO 2 followed by intramolecular electron transfer from the dinuclear ${{\rm Ru}{{{\rm II}{\rm \char44}{\rm III}\hfill \atop 2\hfill}}}$ moiety to photogenerated Ru III was observed. The resulting long‐lived ${{\rm Ru}{{{\rm III}{\rm \char44}{\rm III}\hfill \atop 2\hfill}}}$ state decays on the millisecond timescale.