The electronic structures and relative stabilities of homopolar biradicals (BR) and CTBR with significant one-electron transfer (ET) BR characters were investigated by ab initio MO calculations. The previously presented inter- and intramolecular CT models were extended in order to elucidate possible mechanisms for decomposition reactions of dioxetane, dioxetanone, and related species. The computational results indicate that endothermic O-O cleavages, followed by charge-transfers, are operative for the chemiluminescence reactions of these peroxides with several anionic species, in contradiction to the chemically initiated electron-exchange luminescence (CIEEL) mechanism, where complete one-electron transfer (ET) is required for the formation 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 antibonding orbital. The CT excitation energies are used to distinguish between the CT induced luminescence (CTIL) mechanism and the CIEEL mechanism for chemiluminescence reactions. Orbital-interaction models are also presented to explain of the so-called odd/even selection rule for the efficiency of chemiluminescence reactions. The implications of these results are discussed in relation to recent experimental results, together with biological chemiluminescence reactions of luciferins and related species.
ASJC Scopus subject areas