Photo-oxidation of carboxylic acids via photochemical redox reactions of ion pairs: evaluation of the corrected quantum yields for multi-equilibria acid-base systems

Carboxylic acid anions which form ion pairs with transition metal cations can be oxidized by electron transfer mechanisms promoted by irradiation at the ion pair charge transfer (IPCT) band. The overall quantum yield of the photochemical redox reaction of the ion pair in the presence of various carboxylic acid anions must be corrected for each species present and for the fraction of light absorbed by each reactive ion pair. These calculations require the knowledge of the acid-base equilibria of the organic substrate and the characteristic constants of the ion pair (molar absorptivities and thermodynamic association constants which provide the variation in the concentration of each ion pair over the pH range). It is shown that the variation in the overall quantum yield of the photochemical redox reaction of the ion pair as a function of pH is due to the variation in the concentration of the reactive species present in solution.