Photocatalytic decomposition of dispiro(diadamantane-1,2-dioxetane) initiated by Ce(ClO4)3 in the excited state

Article abstract of DOI:10.1007/BF02495196

Photocatalytic decomposition of dispiro(diadamantane-1,2-dioxetane) (1) to adamantanone (2) initiated by Ce(ClO₄)₃ in the excited state in the MeCN-CHCl₃ (2 : 1) mixture was studied. The bimolecular rate constants of quenching k_q were determined from the kinetics of quenching of Ce³⁺* by dioxetane at different temperatures. The Arrhenius parameters of the quenching were calculated from the temperature dependence of k_q: E_a = 3.2±0.3 kcal mol^-1 and logA = 11.6±0.6. The quantum yields of photolysis of 1 depending on its concentration and the rate constant of the chemical reaction of Ce³⁺* with 1 were determined. The latter coincides with k_q: k_ch = (2.6±0.3) · 10⁹ L mol^-1 s^-1 (T = 298 K). The fact that the maximum quantum yield or decomposition of dioxetane is equal to 1 indicates the absence of physical quenching of Ce³⁺* by dioxetane. It is believed that the electron transfer occurs in the reaction of Ce³⁺* with 1. Nonradiative deactivation of Ce³⁺* in solutions of MeCN and in MeCN-CHCl₃ mixtures was studied. It is caused by the replacement of H₂O molecules in the nearest coordination surroundings of Ce³⁺ by solvent molecules and reversible transfer of an electron to the ligand. The activation parameters of the nonradiative deactivation of Ce³⁺* were determined.