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, DBF<sub>2</sub> : γ-CD<sub>2</sub>. The binding constants have been determined from the fluorescence intensities through the analysis of the <i>F</i><sub>0</sub>/<i>F</i> 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.
Pablo Rodríguez, Miguel Sánchez, José Ramón Isasi, and Gustavo González-Gaitano, "Fluorescence Quenching Investigation of the Complexes of Dibenzofuran with Natural Cyclodextrins," Appl. Spectrosc. 56, 1490-1497 (2002)