Photocatalytic decomposition of dispiro(diadamantane-1,2-dioxetane) initiated by Ce(CIO4)3 in the excited state

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 quenchingk _q were determined from the kinetics of quenching of Ce^3+* by dioxetane at different temperatures. The Arrhenius parameters of the quenching were calculated from the temperature dependence ofk _q:E _a=3.2±0.3 kcal mol⁻¹ and logA=11.6±6. The quantum yields of photolysis of 1 depending on its concentration and the rate constant of the chemical reaction of Ce^3+* with 1 were determined. The latter coincides withk _q:k _ch=(2.6±0.3)·10⁹ L mol⁻¹ s⁻¹ (T=298 K). The fact that the maximum quantum yield of decomposition of dioxetane is equal to 1 indicates the absence of physical quenching of Ce^3+* with 1. Nonradiative deactivation of Ce^3+* 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 Ce^+* were determined. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 724–729, April, 1997.