Kinetics of the photoconversion of diphenylamine in β-cyclodextrin environments

Abstract

Photochemical conversion of diphenylamine (DPA) to carbazole (CAZL) has been studied fluorometrically in aerated aqueous and aqueous β-cyclodextrin (β-CD) environments. The fluorophore forms a 1:1 inclusion complex with β-CD. The quantum yield of the photoreaction is found to remain unaltered in both the environments. However, estimation of the rate constants for the photochemical conversion of DPA to CAZL in the two environments reveals that within the CD environment, rate of the photoreaction is affected remarkably. This has been rationalized from the restriction in the intramolecular rotation for accessing the reaction centres responsible for the photocyclization process. This has also been corroborated from a comparison of the cavity diameter of the β-CD and the optimized geometry of DPA obtained from the semiempirical (AM1-SCI) calculation.