Studies on the Intramolecular Electron Transfer Catalyzed Thermolysis of 1,2-Dioxetanes

This work reports the synthesis and the chemiluminescence properties of the dioxetanes: 4-ethyl-4-methyl-3-(3-methoxyphenyl)-1,2-dioxetane (I), 4-ethyl-4-methyl-3-(3-tert-butyldimethylsilyloxyphenyl)-1,2-dioxetane (II), 4,4-dimethyl-3-(3-methoxybenzyl)-1,2-dioxetane (III) and 4,4-dimethyl-3-(3-tert-butyldimethylsilyloxybenzyl)-1,2-dioxetane (IV). While in the thermal decomposition of I–IV preferential formation of triplet excited states is observed, in the presence of fluoride ions the decomposition rate constants of II and IV increase drastically and singlet excited states are formed with high quantum yields. These results are discussed based on the CIEEL (‘Chemically Initiated Electron Exchange Luminescence’) mechanism where the decomposition of the dioxetanes should be initiated by an intramolecular electron transfer from the phenolate ion (generated by fluoride catalyzed deprotection of the silyloxy group), either directly bound to the peroxidic ring (II) or separated from it by a methylene bridge (IV).