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Recebido em 19/5/00; aceito em 12/3/01 CHEMILUMINESCENCE OF CYCLIC ORGANIC PEROXIDES: GENERATION OF ELECTRONICALLY EXCITED STATES IN 1,2-DIOXETANE DECOMPOSITION. In this review article, we give a general introduction on the mechanisms involved in organic chemiluminescence, where three basic models for excited state formation are presented. The chemiluminescence properties of 1,2-dioxetanes-four membered ring peroxides-are briefly outlined in the second part. In the main part, the mechanisms involved in the decomposition of 1,2-dioxetanes and analogous peroxides are discussed: (i) the unimolecular decomposition of 1,2-dioxetanes; (ii) the electron transfer catalyzed decomposition of peroxides by an intermolecular CIEEL (Chemically Initiated Electron Exchange Luminescence) mechanism; (iii) 1,2-dioxetane decomposition catalyzed by an intramolecular electron transfer mechanism (intramolecular CIEEL). Special emphasis is given to the latter subject, where recent examples with potential analytical applications are presented.

beta- and gamma-lumicolchicines are photoproducts formed by the cycloisomerization of the tropolone ring of colchicine (COL) alkaloids. The mechanism of the photoconversion, suggested to involve the triplet state, is examined here by studying the effect of the solvent polarity on the lumicolchicine photoisomer ratio. Triplet COL, detected by laser flash photolysis, is quenched by oxygen, but not by transtilbene or 1-methylnaphtalene. Neither the quantum yield of conversion of COL nor the photoproduct ratio was altered by the presence of oxygen. Likewise, energy transfer to COL from triplet acetone produced by either isobutanal/horseradish peroxidase system or tetramethyldioxetane thermolysis failed to provoke photoreaction of COL. Our data argue against the intermediacy of a COL triplet state in the photoisomerization and stress on the role of specific solvent-solute interactions in determining the partitioning of excited singlet state into the beta- and gamma-isomer formation.

β‐ and γ‐lumicolchicines are photoproducts formed by the cycloisomerization of the tropolone ring of colchicine (COL) alkaloids. The mechanism of the photoconversion, suggested to involve the triplet state, is examined here by studying the effect of the solvent polarity on the lumicolchicine photoisomer ratio. Triplet COL, detected by laser flash photolysis, is quenched by oxygen, but not by trans‐stilbene or 1‐methylnaphtalene. Neither the quantum yield of conversion of COL nor the photoproduct ratio was altered by the presence of oxygen. Likewise, energy transfer to COL from triplet acetone produced by either isobutanal/horseradish peroxidase system or tetramethyldioxetane thermolysis failed to provoke photoreaction of COL. Our data argue against the intermediacy of a COL triplet state in the photoisomerization and stress on the role of specific solvent–solute interactions in determining the partitioning of excited singlet state into the β‐ and γ‐isomer formation.