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Lookup NU author(s): Emeritus Professor Anthony Harriman
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A binuclear complex has been synthesized having ruthenium(II) bis(2,2′:6′,2″-terpyridine) terminals attached to a central 2,2′-bipyrimidine unit via ethynylene groups. Cyclic voltammetry indicates that the substituted terpyridine is the most easily reduced subunit and the main chromophore involves charge transfer from the metal centre to this ligand. The resultant metal-to-ligand, charge-transfer (MLCT) triplet state is weakly emissive and has a lifetime of 60 ns in deoxygenated solution at room temperature. The luminescence yield and lifetime increase with decreasing temperature in a manner that indicates the lowest-energy MLCT triplet couples to at least two higher-energy triplets. Cations can bind to the central bipyrimidine unit, forming both 1 : 1 and 1 : 2 (ligand : metal) complexes as confirmed by electrospray MS analysis. The photophysical properties depend on the number of bound cations and on the nature of the cation. In the specific case of binding zinc(II) cations, the 1 : 1 complex has a triplet lifetime of 8.0 ns while that of the 1 : 2 complex is 1.8 ns. The 1 : 1 complexes formed with Ba2+ and Mg2+ are more luminescent than is the parent compound while the 1 : 2 complexes are much less luminescent. It is shown that the coordinated cations raise the reduction potential of the central bipyrimidine unit and thereby increase the activation energy for coupling with the metal-centred state. Complexation also introduces a non-emissive intramolecular charge-transfer (ICT) state that couples to the lowest-energy MLCT triplet and provides an additional non-radiative decay route. The triplet state of the 1 : 2 complex formed with added Zn2+ cations decays preferentially via this ICT state. © The Royal Society of Chemistry 2005.
Author(s): Harriman A, Mayeux A, Stroh C, Ziessel R
Publication type: Article
Publication status: Published
Journal: Dalton Transactions
Print publication date: 07/09/2005
ISSN (print): 1477-9226
ISSN (electronic): 1477-9234
Publisher: Royal Society of Chemistry
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