The Chemiluminescence of Indole Derivatives. IV. Correlation between Chemiluminescence and Structure of 2,3-Dimethylindoles

Four 5-substituted and three 6-substituted 2,3-dimethylindoles and unsubstituted 2,3-dimethylindole were synthesized and their light emission was measured in the presence of atmospheric oxygen and potassium t-butoxide in dimethyl sulfoxide. It was found that the Hammett equation was applicable to their chemiluminescent reaction with ρ value of −1.24. For the 6-position of indole nucleus σp was used, and for the 5-position σm was used. Also, four hydroperoxides of 2,3-dimethylindole bearing substituents at the 5- or 6-position, which emitted light in the presence of potassium t-butoxide in dimethyl sulfoxide, gave linear Hammett plots with ρ value of −2.04. The relationship between the Hammett equation and the chemiluminescence of these inole derivatives has been discussed further.