Laser flash photolysis study of the photochemistry of ninhydrin and its 5-methoxy derivative in benzene solution

Abstract

Laser flash photolysis of ninhydrin ( 1) and its 5-methoxy derivative 4, in benzene solution, yields readily detectable transients, which were assigned to their corresponding triplet excited states. By employing this time-resolved technique, rate constants for hydrogen abstraction, electron transfer and energy transfer processes were measured. The quenching rate constants obtained are independent of the ninhydrin structure, being only dependent on the quenching process. These values range from 1.3 × 10 6 M −1 s −1 (cyclohexa-1,4-diene) to 5.9 × 10 9 M −1 s −1 (DABCO) for ninhydrin ( 1) and from 1.8 × 10 6 M −1 s −1 (cyclohexa-1,4-diene) to 7.3 × 10 9 M −1 s −1 (DABCO) for 5-methoxyninhydrin ( 4). The quenching rate constants obtained, characteristic of an nπ * carbonyl triplet, indicate that the photochemistry of 1 and 4 is controlled by the 1,3-dicarbonyl chromophore, despite the presence of the 5-methoxy group in 4.