Studies on Aminodioxetanes as a Model of Bioluminescence Intermediates. 1‐(1‐methyl‐3‐indolyl)‐6‐phenyl‐2,5,7,8‐tetraoxabicyclo[4,2,0]octane, an Aminodioxetane Resulting in Efficient Ultraviolet and Exciplex Chemiluminescence*

The title aminodioxetane prepared by photooxygenation of 2–(l‐methyl‐3‐indolyl‐3‐phenyl‐1,4‐dioxene is fairly stable at −46°C and gives on warming to room temperature an ultraviolet light at Λmax 320 nm, which corresponds to 377kJ/mol; the highest energy ever observed among the efficient chemiluminescent compounds. The efficiency of chemiluminescence and excited singlet molecule formation in n‐hexane were 3.6% and at least 50%, respectively. Substitution and solvent effects suggest polar nature of the transition state as expected from the ‘CIEEL’ mechanism. In polar solvents, the dioxetane gives visible light (Λmax 400 nm in dichloromethane) as well as the UV light; the former being quenched by methanol. This is interpreted in terms of an intramolecular exciplex formation between the indole and phenyl groups. This is the first example of an intramolecular exciplex produced by the dioxetane decomposition.