EFFECT OF THE FORMATION OF INCLUSION COMPLEXES WITH BETA-CYCLODEXTRINON THE PHOTOISOMERIZATION AND FLUORESCENCE PROPERTIES OF AROMATIC NORBORNADIENE DERIVATIVES

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