Intramolecular decomposition chemiluminescence

Intramolecular electron transfer initiated peroxide decomposition. . 1236 HIGH-EFFICIENCY ORGANIC CHEMILUMINESCENT REACTIONS INVOLVING PEROXIDE INTERMEDIATES. 1238... 

Several other examples of 1,2-dioxetane derivatives containing easily oxidizable groups have been reported and the high singlet quantum yield observed in their decomposition was attributed to the occurrence of the intramolecular CIEEL sequence Based on this concept, Schaap and coworkers have introduced the concept of induced chemiluminescence, which is very relevant for investigations into firefly luciferin bioluminescence and has led to the development of chemiluminescent probes widely used in immunoassays (Section N. 

Matsumoto M, Watanabe N. Structural aspects of 1,2-dioxetanes active toward intramolecular charge-transfer-induced chemiluminescent decomposition. Bull Chem Soc Jpn 2005 78 1899-1920. 

This was further elaborated upon by Schuster and co-workers (K21, S23, S24) and by Schaap s group at Wayne State University (S6, S8, SIO, Sll, Z2, Z3). Thus, the observation that some hydroxy-substituted aromatic dioxetanes show high chemiluminescent efficiencies at alkaline pH (phenolic anionic form) led to the formulation of a third mechanism for chemiluminescent decomposition of dioxetanes. This mechanism, known initially as intramolecular electron transfer (Ml9, Z2) and subsequently as chemically initiated electron exchange luminescence, or CIEEL (FI, K20), can be best illustrated by reference to the dioxetane shown in Fig. 37, where the chemiluminescence is triggered by the addition of fluoride ions. 

The electrogenerated chemiluminescence (ECl) of five l-amino-3-anthryl-9-propane derivatives has been studied in tetrahydrofuran. Emission from intramolecular exciplexes in ECl spectra and weak emission from the locally excited anthracene moiety were observed. The influence of triplet state interaction in ECl emission is discussed. The chemiluminescent decomposition of three a-peroxy-lactones gives CO2 and the corresponding ketone in high yield. The chemiluminescent species produced has been investigated in some detail by measurements of lifetime, energy-transfer activation parameters, and photochemical reactions. 

Intramolecular anhydride/peranhydride exchange through in situ formation of a peroxy p-nitrophenyl anhydride intermediate has been inferred to form diphenoyl peroxide, as evidenced by its chemiluminescent decomposition (Scheme 21) <86JOC2050>. 

Structural aspects of 1,2-dioxetanes active toward intramolecular charge-transfer-induced chemiluminescent decomposition 05BCJ1899. 

H02 " as nucleophile [73]. The intramolecular electron transfer is in fact a combination of the hypothesis for the firefly dioxetanone decomposition (p. 152) and the (intramolecular) chemiluminescent activation of secondary peresters (p. 35). However it is only one hypothesis among many which lack confirmatory evidence in this exceedingly complicated reaction. 

The decomposition of the endoperoxide via the o-xylene derivative (48) in an intramolecular electron transfer mechanism would also give the substituents a decisive role in the excitation step itself - not only affecting the fluorescence efficiency of the phthalate dianion. A high fluorescence efficiency is of course a necessary, but not sufficient, requirement in luminol type chemiluminescence [9, 16],... 

Nonetheless, a dioxetan decomposition mechanism for lucigenin chemiluminescence, based on the exergonic processes described in Chap. V, seems well established [3]. A direct demonstration of the intermediacy of this dioxetane was first made [4] in 1969 by treating 10,10 -dimethyl-9,9 -biacrylidene (4) with singlet oxygen from several sources. Emission from N-methyl acridone was unequivocally shown. The lifetime of the intermediate was characteristic of the supposed dioxetane. Intramolecular electron transfer has been suggested as the excitation mechanism in the decomposition of this and other electron-rich dioxetans. 

Although there are many components in a mechanistic description of a chemiluminescent reaction, the heart of the matter is the actual excitation step. Several such steps have been identified. Some are molecular in character e. g. the decomposition of dioxetans and some are intermolecular electron transfer steps. There is an intermediate class in which the step can be formulated as an /n ramolecular electron transfer. Many luminescent reactions have been ascribed to this category with varying degrees of confidence. Cyclic hydrazides such as luminol belong rather uncertainly here. Electron rich dioxetans and dioxetanones and the luciferins with such intermediates on the pathway are a little more reasonably assigned to an intramolecular electron transfer mechanism. Even here however caution is required in that direct evidence for discrete electron transfer will by its very nature be almost impossible to obtain and will probably remain circumstantial. 

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