A new molecular switch based on a symmetrical dinuclear complex of two tricarbonylrhenium(I) moieties bridged by 4,4″-azobis-(2,2′-bipyridine)

Abstract

A new symmetrical dinuclear complex of two tricarbonylrhenium(I) moieties, of formula [(CH3CN)(CO)3Re(4,4″-azobpy) Re(CO)3(CH3CN)](PF6)2, with 4,4″-azobpy = 4,4″-azobis-(2,2′-bipyridine), has been synthesized and characterized by spectroscopic, electrochemical, spectroelectrochemical, photophysical and computational techniques. The bridging azo group in the bipyridyl ring decreases the emission quantum yield of the 3MLCT lowest-lying excited state respect to similar Re(I) complexes and introduces a new emissive excited state with a longer lifetime, due to increased electronic delocalization in the bridging ligand. When reducing the azo group in CH3CN/H2O mixtures with sodium dithionite, the emission is enhanced by an order of magnitude. Therefore, this complex can be used as a ?molecular switch? with electron and proton additions. Besides, changes in the absorption spectrum on addition of L-Cysteine can be applied for sensing aminoacids with reducing thiol groups. The electronic structures calculated by DFT methods agree reasonably well with experimental results.