Six novel europium complexes with phenanthroline derivatives as fluorescence sensor have been prepared, and their structures were characterized by FT-IR, UV–vis, 1 H NMR, 13 C NMR, ESI-MS, and element analysis. All complexes exhibited long luminescent lifetime and high luminescent quantum efficiency (η). Among these complexes, the complex (a) exhibited the lowest luminescent quantum efficiency and shortest lifetime, which was attributed to the presence of OH oscillators in the corresponding ligand HPIP. Spectroscopic studies, including UV–vis, PL and 1 H NMR spectra, showed that these sensors exhibited striking spectra changes in response to CH 3 COO − due to hydrogen bonding interaction of imidazolyl NH groups, aromatic and phenanthroline ring's protons with CH 3 COO − . Particularly, europium complexes (e) and (f) have a remarkable color changes (from transparent to light-yellow), and hence they were convenient to detect the CH 3 COO − with them by naked eye in DMSO solution.