Two novel europium (III) centered anion receptors and their naked eye detections

Two novel luminescent europium (III) tris(dibenzoylmethane) (Eu(dbm)3) with 2-indole-3-yl-imidazo [4,5-f]-1,10-phenanthroline (a) and 2-(2-nitrophenyl)-imidazo [4,5-f]-1,10-phenanthroline (b) complexes were prepared as anion receptors. It was found that Eu(dbm)3(a), which give rise to intense yellow emission, can selectively recognize F− and H2PO4− by changing its color from yellow to green. However, Eu(dbm)3(b) with red emission could generate luminescent quenching by F− and H2PO4−. These sensing materials were characterized by UV–vis, fluorescence and NMR, indicating that the recognition processes were attributed to the synergistic effects of hydrogen-bonding and competitive coordination interactions between the ligands and anions.