The Chemiluminescence of Indole Derivatives. III. On the Mechanism of the Chemiluminescence of 2,3-Dimethylindole and 5-Substituted- 2,3-dimethylindoles in the Dimethyl Sulfoxide - Alkali System

A bright green light is observed on the treatment of a solution of 2,3-dimethylindole (I) and its hydroperoxide (II) in dimethyl sulfoxide (DMSO) with alkali (potassium t-butoxide or granular potassium hydroxide) under streams of oxygen and hydrogen respectively. The change in their ultraviolet and fluorescent spectra with the time and the chemiluminescent spectra is measured. The compound II is concluded to be the reaction intermediate of I; it decomposes to yield an excited singlet state of an o-acetamidoacetophenone anion (III*), a light emitting species in this reaction. The investigation, then extended to four 5-substituted-2,3-dimethylindoles, revealed that three of them displayed chemiluminescence through the same mechanism as in the case of I.