Quenching Reactions of Dioxetans

All of the above brightly luminescent, relatively unstable dioxetans have been considered to decompose by an intramolecular electron transfer mechanism. 

However there are problems associated with this extension from electrochemiluminescence and the m rmolecular CIEEL cases. 

It has already been mentioned that alkyl substituted dioxetans do not normally show exhanced rates of decomposition on intermolecular collision with low ionisation potential fluorescers. The geometric arrangement (particularly orbital overlap) of dioxetan and would-be electron donor in the compounds just discussed is less than ideal. They are in fact simple dioxetans with an ill-disposed electron donor. It is not clear then why they should show electron transfer from these donors (which are sometimes, e.g. in (12), considered unlikely activators in CIEEL) when they would certainly not react that way m ermolecularly. 

Since dioxetans are the only ultimate precursors of the excitation step in chemiluminescence so far isolated, they provide a unique opportunity for the study of dark reactions. 

Oxygen would normally be considered an effective quencher of ketone phosphorescence, yet degassing solutions of dioxetans in the presence of DBA as acceptor [26] brought an increase in rate and a decrease in quantum yield. The explanation appears to be that DB A sensitises the decomposition of the dioxetan and DBA survives longer in oxygen-free solution. 

---