Chemically Initiated Electron Exchange 1,2-dioxetanes

Chemically Initiated Electron Exchange Luminescence (CIEEL) acridinium salts, 1256 alkaline phosphatase, 1193-8 1,2-dioxetanes, 1182-200 firefly bioluminescence, 1191-3 intermolecular, 1213-15, 1231-6 intramolecular, 1214-15, 1236-8 luminol, 1247-8... 

In recent years several new dioxetanes substituted with easily oxidized groups, notably various aminoaryl groups, have been prepared and studied. Also in recent years, the chemically initiated electron-exchange luminescence... 

Chemically initiated electron-exchange luminescence (CIEEL) constitutes a general phenomenon, the important example of which is the firefly bioluminescence. A longstanding mechanistic dichotomy on the CIEEL process concerns concerted versus stepwise cleavage of the dioxetane ring. As it is shown in Scheme 1 (on the left), the... 

Adam W, Bronstein I, Trofimov AV, VasiTev RE. Solvent-cage effect (viscosity dependence) as a diagnostic probe for the mechanism of the intramolecular chemically initiated electron-exchange luminescence (CIEEL) triggered from a spiroadamantyl-substituted dioxetane. J Am Chem Soc 1999 121 958-61. 

The 1,2-dioxetanes are another important group of chemiluminescent compounds. These compounds are oxidatively cleaved thermally in a concerted fashion to yield two carbonyl moieties, one of which is excited. The mechanism of this cleavage has been described as a chemically initiated electron-exchange... 

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 E-diethylstilbestrol-4 ,4 -semiquinone oxygen-centred radical is converted to a carbon centred radical which reacts with Oj forming a di-oxetane. Unless the dioxetane is rapidly protonated, it will almost instantly cleave into excited carbonyl products because of the intramolecular chemically initiated electron exchange luminescence. In the latter, electron transfer from the phenoxide moiety to the peroxide ring promotes the fluorescence observed from the singlet-excited 4-hydroxy propio-... 

The mechanisms fall into two broad classes. In the first there are structural features which predispose the reaction towards the formation of excited states. Two important divisions of this class are represented by peroxides undergoing reaction by chemically initiated electron exchange luminescence (CIEEL) (p. 34) and the dioxetans. However, many of the luminescent reactions of peroxides are not dependent on a unique structure for the peroxide and the exact mechanism of excitation can be as difficult to elucidate as in the cases where the peroxides are not isolated. Dioxetans are a special case and are dealt with in detail in Chap. V. 

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