A novel fluorescent sensor for Al~(3+) and Zn~(2+) based on a new europium complex with a 1,10-phenanthroline ligand

A new europium complex Eu(tta)₃L₁ (1a) based on 1,10-phenanthroline derivative (L₁ = (2-(3,5-dimethoxyphenyl)-1H-imidazo[4,5-f][1,10]phenanthroline), tta = 2-thenoyltrifluoroacetone) was designed and synthesized. Its structure was characterized by ¹H and ¹³C NMR, elemental analysis, UV-vis, fluorescence spectra and single crystal X-ray diffraction. The crystal of the complex 1a belongs to monoclinic system with the space group P2₁/n. The europium complex 1a in the solid and in the solution displays the typical emission of Eu(III) ion centered at 612 nm as a result of the electric dipole transition (⁵D₀ → ⁷F₂). It exhibits high quantum yield (20.42%), long lifetime (0.29 ms) and good CIE color coordinate (0.67, 0.33) in solid. In addition, the complex shows high sensitivity and selectivity towards Al³⁺ and Zn²⁺ in methanol solution which can be attributed to the Al³⁺/Zn²⁺ cation instead of Eu³⁺ in the complex 1a. The LODs for Al³⁺ and Zn²⁺ were calculated to be 5.880 × 10^?7 and 7.678 × 10^?8 mol/L, respectively. Besides, the additions of Al³⁺ and Zn²⁺ express remarkable color changes from red to bright blue and ivory that can be clearly observed by the naked eye respectively.