Synthesis, fluorescence properties and F− detection performance of Eu(III) complexes based on the novel coumarin Schiff base derivatives

Three novel coumarin Schiff base derivatives and corresponding Eu(III) complexes were designed and synthesized. The aggregation-induced emission (AIE) property of ligands was studied. The fluorescence properties and electrochemical properties of Eu(III) complexes were investigated by comparing different substituent groups. The ion selectivity and ion detection limits of the [EuL2(NO3)3] •H2O were also studied. The result indicates that all ligands exhibit the AIE property in CH3CN/H2O solution and emit green fluorescence with the maximum emission wavelength of 552 nm. All complexes show characteristic red fluorescence of Eu(III) and the influence of different substituents on the fluorescence intensity of Eu(III) complexes is ordered: -OCH3 > -H > -NO2, and [EuL2(NO3)3] •H2O exhibits the strongest fluorescence intensity. The density functional theory (DFT) calculations of the ligands indicate that the introduction of electron-donating groups increases the HOMO energy level and the electron cloud density, which enhance the ability to coordinate with Eu(III) and the fluorescence intensity of the corresponding complex. Besides, the electrochemical properties of Eu(III) complexes indicate that the introduction of electron-donating groups increases the energy gaps (Eg) and the conjugation of the complex, which enhances the fluorescence intensity of the complexes. Ion selectivity experiments show that [EuL2(NO3)3] •H2O has a specific recognition function for F−, and its response limit is between 1.0 × 10−5 mol·L−1 and 2.2 × 10−5 mol·L−1. Based on the above results, all the ligands and Eu(III) complexes have a promising application in optical materials due to the excellent fluorescence properties. In addition, All Eu(III) complexes also have a potential application prospects in the field of fluoride ion detection.