EFFECT OF CYCLODEXTRIN COMPLEXATION ON THE PHOTOCHEMISTRY OF XANTHONE - ABSOLUTE MEASUREMENT OF THE KINETICS FOR TRIPLET-STATE EXIT

The photochemistry of xanthone aqueous solutions has been examined in the presence of cyclodextrins (α-, β-, and Γ-CD). From spectrophotometric measurements it is concluded that xanthone forms 1:1 inclusion complexes with all cyclodextrins and that association is most favored in the case of β-cyclodextrin. Laser flash photolysis studies provide valuable information on the association/dissociation kinetics of the inclusion process. Following excitation, the xanthone triplet relocates from the cyclodextrin cavity into the aqueous phase with exit rate constants of the order of 107 s-1; we propose that this relocation is triggered by a change in dipole moment that leads to solubility changes between the ground and triplet states. The effect is most dramatic with β-cyclodextrin, reflecting the strong ground-state association between xanthone and this oligosaccharide. © 1990, American Chemical Society. All rights reserved.