Voltammetric Determination of the Reversible Redox Potential for the Oxidation of the Highly Surface Active Polypyridyl Ruthenium Photovoltaic Sensitizer cis ‐ Ru ( II ) ( dcbpy ) 2 ( NCS ) 2

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Abstract
The electrochemical oxidation of the ruthenium photosensitizer (dcbpy = 2,2′‐bipyridine‐4,4′‐dicarboxylic acid) has been studied in a variety of solvents. Unlike the reversible diffusion‐controlled one‐electron oxidation of (bpy = 2,2′‐bipyridine) to the Ru(III) analogue, complex surface‐based reactions as well as chemical reactions are coupled to the charge‐transfer process under conditions of cyclic voltammetry at macrodisk electrodes. The extent of surface activity was found to be greater in acetone and acetonitrile than in dimethylformamide or tetrahydrofuran and on glassy carbon and gold than on platinum electrodes. An electrochemical quartz crystal microbalance study demonstrates that attachment of solid occurs under open‐circuit conditions, but that much of the material is lost from the surface at potentials prior to the reversible value. Detailed studies in acetone reveal that cyclic voltammograms obtained at macrodisk electrodes are heavily perturbed by surface‐based processes at high concentrations and low scan rates. In contrast, microdisk and rotated disk voltammograms enable an essentially mass transport controlled process to be observed with minimal influence from surface‐based reactions. The application of chemical modification of the electrode surface, steady state (microdisk electrode), fast scan voltammetric and hydrodynamic techniques (rotated disk electrode) to minimize the influence of the surface‐based processes and chemical reactions coupled to the charge‐transfer process are discussed and reversible potentials measured for the mass transport controlled, solution phase redox couple are reported in acetone, acetonitrile, tetrahydrofuran, and dimethylformamide. © 1999 The Electrochemical Society. All rights reserved.

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