Kinetic Studies of the Oxidationof Coumarin-540 Laser Dye

Summary.  3-(2-Benzothiazolyl)-7-diethylaminocoumarin (C-540) has been irradiated at 254 nm in halomethane solvents, and the first order rate constant of the photo-oxidation reaction was determined. The hydrogen bond donation of the solvents plays a substantial role in controlling the rate of formation of the photoproduct. The linearity of the isokinetic relationship supports the similarity of the mechanism in all solvents and emphasizes that the activation process is controlled by diffusion of dye into the solvent cage. Moreover, the chemical oxidation of C-540 with peroxodisulfate anion catalyzed by Ag⁺ ions has been studied. The reaction follows second-order kinetics, first order for each individual reactant. Received October 4, 1999. Accepted (revised) February 14, 2000