Fluorescence Quenching Investigation of the Complexes of Dibenzofuran with Natural Cyclodextrins

Abstract

The steady-state fluorescence of dibenzofuran (DBF) in aqueous solution is quenched in the presence of natural cyclodextrins (CDs), α, β, and γ-CD. The decrease in the fluorescence is static in nature for all the macrocycles and follows as a result of the formation of inclusion complexes of dominant 1:1 stoichiometry. With γ-CD, excimer emission is detected at high CD concentrations due to the formation of a complex of 2:2 stoichiometry, DBF₂:γ-CD₂. The binding constants have been determined from the fluorescence intensities through the analysis of the F₀/F vs. [CD] plots, resulting in a stronger association for β-CD. The thermodynamic parameters of the binding, enthalpy and entropy, have been calculated from the temperature dependence of the formation constants. The different trend displayed by α-CD, in both the absorption and fluorescence spectra, seems to be related to a shallow inclusion of DBF, stabilized by hydrogen bonding between the oxygen atom of the furan ring and the hydroxyl groups of CD.