Benzothiazole appended lower rim 1,3-di-amido-derivative of calix[4]arene: synthesis, structure, receptor properties towards Cu<SUP>2+</SUP>, iodide recognition and computational modeling

A new molecular fluorescent sensor (L) for Cu<SUP>2+</SUP> 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 Cu<SUP>2+</SUP> among eleven divalent ions, viz., Mn<SUP>2+</SUP>, Fe<SUP>2+</SUP>, Co<SUP>2+</SUP>, Ni<SUP>2+</SUP>, Cu<SUP>2+</SUP>, Zn<SUP>2+</SUP>, Cd<SUP>2+</SUP>, Hg<SUP>2+</SUP>, Ca<SUP>2+</SUP>, Mg<SUP>2+</SUP> and Pb<SUP>2+</SUP>, studied. The 1:1 stoichiometry of the complex formed between L and Cu<SUP>2+</SUP> has been demonstrated by electronic absorption and ESI-MS. The role of calix[4]arene for the selective sensing of Cu<SUP>2+</SUP> has been established by comparing the data with that obtained for an appropriate control molecule. The minimum concentration at which L can detect Cu<SUP>2+</SUP> has been found to be 403 ppb. The computations carried out at DFT level have provided the coordination and structural features of the Cu<SUP>2+</SUP> complex of L as species of recognition. The Cu<SUP>2+</SUP> complex thus formed recognizes iodide by bringing change in the color, among the 14 anions studied