One of the most efficient sensitizers presently available for photoelectrochemical solar cell applications is a ruthenium dye based on a terpyridine ligand. The voltammetric oxidation of the N,N,N-bonded thiocyanate isomer of [(H-3-tctpy)Ru-II(NCS)(3)](-)(H-3-tctpy = 2,2':6',2 " -terpyridine-4,4',4 " -tricarboxylic acid), which is relevant to the use of the dye in photovoltaic cells, has been studied at platinum, gold, and glassy carbon electrodes. In acetonitrile, the metal-based one-electron oxidation process for the N,N,N-bonded isomer exhibits close to chemically reversible behavior under a wide range of voltammetric conditions, although the presence of surface-based reactions coupled to the charge transfer process are evident. The electrochemical quartz crystal microbalance technique revealed that dye material is adsorbed onto the electrode surface under open circuit conditions and that additional surface-based oxidation processes occur at potentials more positive than the initial metal-based oxidation process. Oxidative voltammetry in acetone is similar to that in acetonitrile. However, studies on mixtures containing S-bonded linkage isomers in this solvent show a shift in reversible potential to less positive values and a decrease in the contribution of the surface-based processes. In dimethylformamide, low temperatures (T = -55 degreesC) are necessary to observe a reversible one-electron oxidation process. Data are compared to those reported with the more commonly used [(2,2'-bipyridine-4,4'-dicarboxylicacid)(2)Ru(NCS)(2)] sensitizer. (C) 2001 The Electrochemical Society. All rights reserved.