Effect of methylene spacers on the spectral, electrochemical, and structural properties of bis(4,4′-disubstituted-2,2′-bipyridyl) ruthenium(ii) dye analogues

Abstract

Two new ruthenium complexes, [Ru(L₁^OMe)₂(NCS)₂] and [Ru(L₂^OMe)₂(NCS)₂] (where L₁^OMe = 2,2′-bipyridine-4,4′-di(methyl ethanoate) and L₂^OMe = 2,2′-bipyridine-4,4′-di(methyl propionate)), have been synthesized and characterized using spectroscopic and electrochemical techniques. The [Ru(L₂^OMe)₂(NCS)₂] complex has also been characterized by X-ray diffraction studies and reveals a distorted octahedral coordination geometry about the ruthenium center. Cyclic voltammetry studies of both complexes exhibit quasi-reversible Ru(II/III) couples and a number of ligand reduction events. The complex with one methylene spacer between the bipyridyl ligand and the methyl ester functional group, [Ru(L₁^OMe)₂(NCS)₂], was particularly unstable under reducing conditions. The properties of these complexes are compared with the ethyl ester analogue of the N3 photosensitizer [Ru(L₀^OEt)₂(NCS)₂].