Effect of the formation of inclusion complexes with β-cyclodextrin on the photoisomerization and fluorescence properties of aromatic norbornadiene derivatives

The valence photoisomerization of four aromatic norbornadiene (NBD) derivatives has been studied in ethanol and in 0.01 M beta-cyclodextrin (beta-CD) water-ethanol (v/v, 99/1) solution (WECD). Observed first-order rate constants are found to be of the same order of magnitude in ethanol and WECD, ranging between 0.1 and 0.28 s(-1), according to the compound. These photoisomerization kinetic properties are attributed to the formation of inclusion complexes between NBDs and beta-CD. The stoichiometry is 1 : 1, and association constants ranging between 310 and 390 M-1 have been determined fluorimetrically, using Benesi-Hildebrand plots and a nonlinear regression method. The structure of the inclusion complexes is discussed on the basis of AMI semiempirical dimension calculations and photophysical properties.