Coptisine (COP) emits weak fluorescence in acidic (pH 2) aqueous solution. However, a remarkable increase in fluorescence intensity is observed when p-sulfonated calix[4]arene (SC4A) is added to the aqueous solution. With the addition of ionic liquid, the aqueous solution of COP-SC4A complexes considerably quenches fluorescence intensity. The supramolecular interactions of SC4A with three types of 1-butyl-3-methylimidazolium ionic liquids (C4MIm+) were examined based on this fluorescent probe system. The 1-butyl-imidazolium moiety of ionic liquid was embedded in the SC4A cavity, and the counter anion slightly affected the binding capacity of the ionic liquid. 1H-NMR studies and molecular modeling theoretical calculations confirmed the formation of inclusion complexes.

Hai Long Liu, Yan Zhao, Qian Du, Li Ming Du, Tao Tao Pang and Yun Long Fu