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

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+.