Binding of 2-Acetylnaphthalene to γ-Cyclodextrin: Stoichiometry of the Dimer Complex

Naphthalene derivatives have the capability of forming higher order complexes than the typical 1:1 stoichiometry with all three of the common cyclodextrins (α, β, and γ). The 2-acetylnaphthalene (2-AN)/γ-cyclodextrin (γ-CD) system exhibits a long wavelength fluorescence emission at higher γ-CD concentrations, which has been assigned to an excimer band from bound 2-AN dimer. On the basis of the fact that only free 2-AN and the bound dimer fluoresce in this system, we have proposed mathematical models to decide whether the dimer formula is (2-AN) 2 /γ-CD or (2-AN) 2 /(γ-CD) 2 . Our analysis indicates that the latter formula is the correct one. This result is unanticipated, given the fact that a single γ-CD cavity could accommodate two naphthalene rings.