Quenching of a polypyridyl-ruthenium(II) chromophore by covalently attached {ML(NO)Cl} fragments (M=Mo, W; L=tris(3,5-dimethylpyrazolyl)hydroborate)

Abstract

The preparation of a series of binuclear complexes is described, in which 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)hydroborate) via the pendant phenolate. The electrochemical and UV-Vis spectroscopic properties of the binuclear complexes are approximately the sum of those of the component complexes, indicating a small or moderate ground-state interaction between the two fragments. The Mo and W fragments 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 might be feasible. Luminescence studies of the binuclear complexes at 77 and 298 K indicate that quenching of the ruthenium centre does take place and that the mechanism is likely to be energy transfer rather than electron transfer, resulting in a non-luminescent excited state of the Moor W fragment.