Photochemistry of the Co(Sep)³⁺I^- system: evaluation of the quantum yield for the photochemical redox reaction of the ion pair

Spectrophotometric measurements in the region of the ion pair charge transfer band of the Co(Sepulchrate)³⁺I^- system were used to assess the role played by the adducts between the complex cation and iodide anion in the photochemical behaviour of the system. No clear evidence was obtained for the presence or absence of 1:2 or higher adducts and the association constant and molar absorptivity of the 1:1 adduct (ion pair) could not be determined with a satisfactory accuracy. Nevertheless, reliable values were evaluated for the fraction of the exciting light absorbed by the ion pair in the photochemical experiments, and these values were used to correct the previously reported quantum yields, which were based on the total amount of light absorbed by the solutions. The "true" quantum yields for the ion pair are discussed in relation to the proposed reaction mechanism.