Ab initio molecular orbital studies on the chemiluminescence of 1,2-dioxetanes

The mechanism of chemiluminescence of 1,2-dioxetane (DO) and 3,3,3,4-tetram ethyl-1,2-dioxetane (TMDO) are investigated by the ab initio molecular orbi tal calculation. The rate-determining step of the chemiluminescent reaction is the O-O bond breaking to form the biradicals. The potential energies al ong the reaction path are calculated by uB3LYP and uB3P86 methods with 6-31 +G(d); the calculated potential barriers are in reasonable agreement with e xperimental activation energies. An overview of the potential surfaces for overall reaction is obtained. The intersystem crossing mechanism from the s inglet biradical to the triplet state is investigated, and the reaction pat h is followed to the (3)(n pi*) and the reaction path is followed to the (3 )(n pi*) excited states of the carbonyl group of respective fragment molecu les. The mechanism of promotion to the (1)(n pi*) excited state of formalde hyde is investigated by the MCSCF method on DO. The reaction rates and the yield of chemiluminescence are discussed by the RRKM theory of unimolecular reaction.