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

Abstract

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 Ce3+* 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 Ce3+* 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 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 Ce+* were determined.