1,2-Dioxetanes phosphorescence

High yields of excitation without strong visible emission are possible if 0p is very low, as is the case for simple dioxetans. Phosphorescence is difficult to observe under the conditions of most of the reactions, but in principle 0phos can replace 0p. 

Phosphorescence emission from triplet states of carbonyl compounds formed through dioxetane decomposition can only be observed under specific conditions in the absence... 

Emission of phosphorescence by 1,2-dioxetanes and a-peroxylactones has also been observed, but is quite rare. Thus, in degassed acetonitrile the 430 nm emission exhibited by the tetramethyl-l,2-dioxetane (7) has been assigned to acetone phosphorescence. Similarly, this acetone phosphorescence has been detected for the dimethyl-a-peroxylactone. ° For the acetyl derivative (19), both the n,TT fluorescence and phosphorescence of 2,3-butanedione have been reported. Thus, if the photoexcited luminescence spectrum of the carbonyl product is known or can be readily measured, the chemiluminescence spectrum can be used as corroborative structure confirmation of the 1,2-dioxetane or a-peroxylactone. 

Dioxetanes such as tetramethyl-1,2-dioxetane (525) are known to undergo thermal decomposition to form two carbonyl compounds via a concerted or stepwise (radical) mechanism, accompanied by chemiluminescence (Section 5.6) (Scheme 6.254).135,511,1440 The degradation of 525 results principally in acetone phosphorescence (2max = 430 nm) and the reaction is very sensitive to quenching by oxygen. 

Phosphorescence from photo-Qxcitcd acetone (the triplet being formed from the singlet by intersystem crossing) is very much less [19]. Thus the triplet ketone appears to be formed directly in the decomposition of the dioxetan. The yield of excited singlet in the thermal decomposition is almost always about 100 times less than that of the triplet. 

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. 

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