Theoretical studies of decomposition reactions of dioxetane, dioxetanone, and related species. CT induced luminescence mechanism revisited

The electronic structures and relative stabilities of homopolar biradicals (BR) and CT BR with significant one-electron transfer (ET) BR characters we re investigated by ab initio MO calculations. The previously presented inte r- and intramolecular CT models were extended in order to elucidate possibl e mechanisms for decomposition reactions of dioxetane, dioxetanone, and rel ated species. The computational results indicate that endothermic O-O cleav ages, followed by charge transfers, are operative for the chemiluminescence reactions of these peroxides with several anionic species, in contradictio n to the chemically initiated electron-exchange luminescence (CIEEL) mechan ism, where complete one-electron transfer (ET) is required for the formatio n of excited carbonyl fragments. The ionization potentials of monoanions of phenol, indole and luciferins were calculated semiempirically in order to estimate the CT excitation energies from these species to the O-O antibondi ng orbital. The CT excitation energies are used to distinguish between the CT induced luminescence (CTIL) mechanism and the CIEEL mechanism for chemil uminescence reactions. Orbital-interaction models are also presented to exp lain of the so-called odd/even selection rule for the efficiency of chemilu minescence reactions. The implications of these results are discussed in re lation to recent experimental results, together with biological chemilumine scence reactions of luciferins and related species.