QUENCHING OF A POLYPYRIDYL-RUTHENIUM(II) CHROMOPHORE BY COVALENTLY ATTACHED (ML(NO)CL) FRAGMENTS (M=MO, W, L=TRIS(3,5-DIMETHYLPYRAZOLYL)HYDROBORATE)

The preparation of a series of binuclear complexes is described, in wh ich derivatives of [Ru(bipy)(3)](2+) bearing a peripheral phenol group attached to the 4-position of one of the bipyridyl ligands are linked to {ML(NO)Cl} fragments (M=Mo, W; L=tris(3,5-dimethylpyrazolyl)hydrob orate) via the pendant phenol ate. The electrochemical and UV-Vis spec troscopic properties of the binuclear complexes are approximately the sum of those of the component complexes, indicating a small or moderat e ground-state interaction between the two fragments. The Mo and W fra gments undergo quasi-reversible one-electron reductions at potentials less negative than the first ligand based reduction of the Ru fragment , suggesting that oxidative quenching of the excited Ru chromophore mi ght be feasible. Luminescence studies of the binuclear complexes at 77 and 298 K indicate that quenching of the ruthenium centre does take p lace and that the mechanism is likely to be energy transfer rather tha n electron transfer, resulting in a non-luminescent excited state of t he Mo or W fragment.