Effect of cyclodextrin encapsulation on the photocyclization of diphenylamine: Cavity imposed restriction on the reaction rate

Abstract

ABSTRACT1he kinetics of the photocyclization of diphenylamine (DPA) to carbazole (CAZL) has been studied fluorometrically in air-equilibrated aqueous solution as well as in constrained microheterogeneous media provided by ct-, 13-, and ~,-cyclodextrins (CDs). It is observed that the fluorophore is embedded within the CD cavities without any alteration of the overall reaction quantum yield in the different environments. However, the rate of the photoreaction is modified remarkably within the CD environments. A restriction on the intramolecular rotation of the phenyl planes of DPA, imposed by the steric rigidity within the CD cavities, has been ascribed to be responsible for the suppression of the reaction rates within the CD environments. A semi-empirical (AMI) calculation gives the molecular dimension of the substrate and corroborates the proposition fi'om a consideration of the cavity size of the different cyclodextrins.

The Photoinduced Electrocyclization Reaction of Triphenylamine (TPA) in Sustainable and Confined Micellar Solutions: A Steady‐State and Laser Flash Photolysis Approach

“…Interestingly, while cyclization of the chalcone derivative occurs at the hydrophobic side of the AOT reverse micelle interface, the generated flavylium ion move to the water pool, where the retro-cyclization slowly occurs. [18] Studies on the 6π-electrocyclization reaction of diphenylamines in different micro-heterogeneous media, including human or bovine serum albumin [19] and cyclodextrin [20,21] have been previously reported in literature, [15][16][17][18] revealing that confined environments exert positive effects on the photocyclization process. In particular, significant micellar effects have been observed for the photoinduced conversion of Nmethyldiphenylamine to the corresponding N-methylcarbazole in SDS and CTAB micellar solutions.…”

“…Studies on the 6π‐electrocyclization reaction of diphenylamines in different micro‐heterogeneous media, including human or bovine serum albumin [19] and cyclodextrin [20,21] have been previously reported in literature, [15–18] revealing that confined environments exert positive effects on the photocyclization process. In particular, significant micellar effects have been observed for the photoinduced conversion of N ‐methyldiphenylamine to the corresponding N ‐methylcarbazole in SDS and CTAB micellar solutions [22] .…”

Enhanced Photochemical [6π] Electrocyclization within the Lipophilic Protein Binding Site

“…Upon encapsulation, the photobehavior of guest molecules is modulated not only as a result of conformational restrictions imposed by the rigidity of protein cavities, but also by the controlled diffusion of oxygen . These two aspects have been previously tackled by comparing the kinetic parameters of N -methyldiphenylamine photocyclization in micro-heterogeneous media with those obtained in water. , In the case of cyclodextrins, a lower rate of photocyclization has been determined and attributed to restricted rotation inside the rigid oligosaccharide structure . By contrast, no significant micellar effect has been found within SDS or CTAB vesicles …”