TRANSIENT INTERMEDIATES IN THE LASER FLASH-PHOTOLYSIS OF KETOPROFEN IN AQUEOUS-SOLUTIONS - UNUSUAL PHOTOCHEMISTRY FOR THE BENZOPHENONE CHROMOPHORE

The transient intermediates in the nanosecond laser flash photolysis o f ketoprofen, an aryl propionic acid, show the formation of a carbanio n in aqueous solutions at pH 7.1. This carbanion incorporates spectros copic properties from both a ketyl radical anion and a benzylic radica l. The ketoprofen carboxylate undergoes biphotonic photoionization, a process that contributes less than 10% to its photodecomposition and l eads to a benzylic-type radical after decarboxylation with a rate cons tant greater than or equal to 1 x 10(7) s(-1). On the other hand, the carbanion forms monophotonically and the unsuccessful attempts to sens itize the formation of the ketoprofen triplet excited state in aqueous solutions suggest that the carbanion precursor is either an excited s inglet state or an extremely short-lived triplet. In organic solvents of lower polarity, the excited triplet state is readily detectable.