Synthesis and electrochemical properties of poly[3-{omega-[4-(2,2'-bipyridyl)]alkyl}thiophenes], P{B(n)T}, and of poly[Ru(II){B(n)T}(3)(2+)]

The electropolymerization of a series of ligands 3-{omega-[4-(2,2'-bipyridyl)]alkyl)thiophene (B(n)T; n = 2, 5, 7, 9, 11) and their tris(ligand)ruthenium(II) complexes, [Ru{B(n)T}(3)](2+), is reported. The electrochemical properties of the polymers were investigated using cyclic voltammetry, chronoamperometry and a.c. impedance spectroscopy. These studies reveal the dependence of the electrochemical behavior of the poly[Ru{B(n)T}(2+)(3)] films upon the length of alkyl chains between the thiophene and the bipyridyl groups, and on the supporting electrolytes; longer alkyl chains induce more irreversible voltammetric behavior and larger charge transfer resistances in the cathodic processes of the polymers. On the basis of these investigations, the mechanism of charge transfer in the polymer-modified electrodes has been evaluated, and interpreted. This shows that electrochemical processes of the polymers in the anodic region are controlled both by kinetic and diffusion factors, whereas the primary influences in the cathodic region are associated with kinetic factors arising from the alkyl chains.