A Cl- anion-responsive luminescent Eu3+ complex with a chiral tripod: Ligand substituent effects on ternary complex stoichiometry and anion sensing selectivity

A new series of N-3, O-mixed donor tripods was prepared for luminescent Eu3+ complexes, in which the soft quinoline nitrogen, tertiary amine nitrogen, and hard amide oxygen donors were cooperatively involved. The mixed donor tripods formed more stable 1 : 1 complexes with Eu( NO3)(3), La( NO3)(3) and Tb(NO3)(3) than the corresponding N-4 donor tripods, and their Eu3+ complexes particularly exhibited anion-responsive luminescence properties. NMR, UV, and luminescence spectroscopic characterizations revealed that -CH3 substitution on the tripod skeleton remarkably altered the preferred stoichiometry of the tripod -Eu3+ - anion ternary complex and gave anion-dependent europium luminescence. Although the disubstituted tripod preferred to form non-luminescent 2 : 1 ( tripod : Eu3+) complexes with Eu( NO3)(3) and other salts, it formed a luminescent 1 : 1 complex with EuCl3. Thus, this type of tripod offered Cl- anion- selective luminescence enhancement that was easily observed by the naked eye.