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 [(CH 3 CN)(CO) 3 Re(4,4″-azobpy) Re(CO) 3 (CH 3 CN)](PF 6 ) 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 3 MLCT 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 CH 3 CN/H 2 O 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.