Anion-responsive luminescent Eu3+ complexes with ring-like rigid quinoline–amide ligands

Two novel ring-like rigid quinoline–amide ligands, 2-[2-(1,3-dioxolan-2-yl)quinolin-8-yloxy]-N-benzylacetamide (LI) and 3-[2-(1,3-dioxolan-2-yl)quinolin-8-yloxy]-1,1-diphenylpropan-2-one (LII), were designed to assemble the anion-responsive luminescent europium complexes. Crystallographic studies of the EuLI(NO3)3 and EuLII(NO3)3 revealed that the tetradentate ligands LI and LII cooperatively coordinated with Eu3+ ion and some available sites around central europium ions for guest anions were reserved in the complexes. The luminescent properties of the Eu(III) nitrate complexes in acetonitrile solutions were investigated. And the lowest triplet state energy levels of the ligands are well placed to allow energy transfer to the resonance level of Eu(III). At the same time, the luminescence titration experiments and the Jobʹs plot analysis demonstrated the formation of 1:1 complexes in the solutions. The luminescence intensities at 616 nm were enhanced by addition of NO3− or Cl− anion to the mixed acetonitrile solutions of Eu(CF3SO3)3 and the ligands.