Steady-state and time-resolved fluorescence techniques were used to study the behavior of 2(I),3(I)-O-(o-xylylene)-per-O-Me-alpha- and -beta-cyclodextrins in aqueous solution, based on the fluorescence of the bidentate xylylene moiety. Fluorescence decay profiles obtained upon excitation of the xylylene group were fitted to three-exponential decay functions. In addition to a fast component due to stray and/or scattered light, two other components ascribed to the monomer and dimer species, respectively, were identified. The dimer/monomer ratio increases with concentration and decreases with temperature, which is in agreement with an enthalpy-driven association process. The corresponding dimerization equilibrium constants (K-D) were obtained from nonlinear regression analysis of the plots of against [CD] in the 5-45 degrees C range. A linear van't Hoff analysis for K-D allows us to obtain the Delta H and Delta S associated to dimer formation. Molecular mechanics as well as molecular dynamics calculations in the presence of water were also employed to study the conformational behavior of such secondary-face-substituted cyclodextrins and rationalize the dimerization processes.