Synthesis and fluorescent properties of europium(III) complexes based on novel coumarin derivatives

Four novel coumarin fluorescence small-molecules were successfully prepared and validated by proton nuclear magnetic resonance (1 H-NMR), carbon-13 (13 C)-NMR, and mass spectrometry (MS). Their corresponding europium(III) complexes were synthesized and characterized. The ligand can emit green fluorescence in solutions, and the best concentration was 40 μmol/L. The emission peak of ligand has a red-shift with the increase of concentration and solvent polarity. And the effect of various substituents in ligand was ordered using fluorescence intensity as standard: -NO2 > -Cl > -OCH3 > -OH. The order of fluorescence quantum yield is in line with the order of fluorescence intensity. The title europium complexes exhibit red fluorescence of europium ion (Eu3+ ) with good thermal stability. The effect of various substituents in ligand on the fluorescence intensity of title europium complexes was also consistent with the earlier results. This suggests that the prepared coumarins fluorescence small-molecules and their corresponding europium complexes have potential application prospects in the field of optical materials.