Spectral study on the interaction of cryptophane-A and neutral molecules CH_nCl_{4 - n} (n = 0, 1, 2)

Cryptophane-A was synthesized from vanillin by a three-step method and its spectroscopic properties in different organic solvents were determined. Two absorption bands at about 240-250 and 280-290 nm were observed for cryptophane-A. A fluorescence emission peak was obtained at 320-330 nm using a solution of ∼10^-5 M cryptophane-A. The interaction of cryptophane-A with chlorinated compounds CH_nCl_{4 - n} (n = 0, 1, 2) in dioxane and ethyl acetate solvents were studied in detail by fluorescence spectroscopy, respectively. The results show that cryptophane-A is well suited for inclusion of CH₂Cl₂ to form a stable 1:1 complex and the binding constant was estimated to be 19 ± 2 M^-1. These results were also confirmed by ¹H NMR and CPK models. Larger similar molecules such as CHCl₃ and CCl₄ are unable to enter the cavity of cryptophane-A because of their bigger sizes. However, the fluorescence emission of cryptophane-A can be efficiently quenched by CHCl₃ and CCl₄, following the Stern-Volmer relationship.