Electropolymerization of trans-[RuCl2(vpy)4] complex—EQCM and Raman studies

Abstract

The electropolymerization of trans-[RuCl2(vpy)4] (vpy=4-vinylpyridine) on Au or Pt electrodes was studied by cyclic voltammetry, electrochemical quartz crystal microbalance (EQCM) technique, and Raman spectroscopy. Cyclic voltammetry of the monomer at a microelectrode shows the typical Ru(III/II) and Ru(IV/III) waves, together with the vinyl reduction waves at −1.5 and −2.45 V and adsorption wave at −0.8 V. Electrodeposition on EQCM technique performed under potential cycling between −0.9 and −2.0 V revealed that the polymerization proceeded well in advance of the vinyl reduction waves. At potentials more positive than −0.9 V, soluble oligomers were deposited irreversibly on the electrode during the oxidative sweep. The film also showed reversible mass changes due to the oxidation and accompanying ingress of charge-balancing anions and solvent into the film. In contrast, potentiostatic growth of the polymer at −1.6 V was slower because the oligomeric material was lost completely from the electrode. Unreacted vinyl groups were detected by in situ Raman spectroscopy for films grown at −0.7, −0.9, and −1.6 V but were absent when the polymerization was carried out at −2.9 V vs Ag/Ag+.