Spectral study on the interaction of cryptophane-A and neutral molecules CHnCl4 − 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 CHnCl4 − 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.