1,2-Dioxetanes, Formation, Mechanism of Thermolysis and Efficiency of Excited State Carbonyl Production.

Applications of chemical reactions to produce light (chemiluminescence, CL) has been used for marking and viewing, and for analytical purposes. 1,2-Dioxetanes have been one of the most important types of compounds in studies of CL processes. Research was directed to a study of the mechanism of dioxtane thermolysis. Since the Cl process will be intimately related to the mechanism of thermolysis, we have been interested to define the parameters that control the mechanism. Currently three mechanisms are considered: (1) stepwise biradical; (2) concerted; and (3) electron transfer (CIEEL). A key intermediate in the thermolysis of dioxetanes by the stepwise process is the 1,4-dioxy biradical. Attempts were made to estimate the lifetime of this biradical by competitive beta-scission and by trapping with hydrogen atom donors. The efficiency of producing an excited carbonyl product from a dioxetane varies widely. Both electronic and steric effects influence the efficiency. To study soley electronic effects, we prepared a series of para-and meta-substituted 3-aryl-3-methyl-2,2-dioxetanes, where steric effects are held constant. Both electron releasing and electron withdrawing groups decrease the triplet efficiency. We observed triplet, singlet energy transfer with (6,12-dibromotetracene) (DBT) and acetophenones, but not with DBT and alkanones.