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Two novel coumarin derivatives and the corresponding europium complexes were prepared using a simple procedure. The pH response of the ligand and the aggregation‐induced emission (AIE) properties of the target europium complex were studied. The ligand had an intramolecular charge transfer (ICT) effect and was linearly and sharply responsive under acidic conditions. The goal europium complexes exhibited excellent AIE performance when subjected to increasing concentrations of target europium complex or proportion of poor solvent. The effect of substituents on fluorescence strength or thermogravimetric and electrochemical properties was further investigated. The target complexes displayed the typical fluorescence of europium. The fluorescence amplitude of the target europium complexes was enhanced by the addition of electron‐donating groups to ligands. Thermogravimetric research findings indicated that the target complexes possessed extreme thermal stability. Electrochemistry discovery findings indicated that the highest occupied molecular orbit energy level of EuL1 was greater than EuL2, but the lowest unoccupied molecular orbit energy level was smaller than that of EuL2. These complexes could be applied in medicinal chemistry, substance chemistry, and fluorescence labelling areas.

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Four novel coumarin fluorescence small‐molecules were successfully prepared and validated by proton nuclear magnetic resonance (1H‐NMR), carbon‐13 (13C)‐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.