Benzothiazole appended lower rim 1,3-di-amido-derivative of calix[4]arene: Synthesis, structure, receptor properties towards Cu2+, iodide recognition and computational modeling

A new molecular fluorescent sensor (L) for Cu2+ has been synthesized by derivatizing the lower rim of calix[4]arene with benzothiazole moiety, through amide linkage to result in 1,3-di-derivative. The receptor molecule, L exhibited fluorescence quenching towards Cu2+ among eleven divalent ions, viz., Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+, Ca2+, Mg2+ and Pb2+, studied. The 1:1 stoichiometry of the complex formed between L and Cu2+ has been demonstrated by electronic absorption and ESI-MS. The role of calix[4]arene for the selective sensing of Cu2+ has been established by comparing the data with that obtained for an appropriate control molecule. The minimum concentration at which L can detect Cu2+ has been found to be 403 ppb. The computations carried out at DFT level have provided the coordination and structural features of the Cu2+ complex of L as species of recognition. The Cu2+ complex thus formed recognizes iodide by bringing change in the color, among the 14 anions studied.