Self-assembly aggregation-induced emission from Eu (III) complexes with o-hydroxy-benzophenone ligands

In this work, europium (III) complexes were synthesized by using different o-hydroxy-benzophenone ligands, namely 2-hydroxy-4-octyloxybenzophenone (HL ₁), 4-allyloxy-2-hydroxybenzophenone (HL ₂) and 2-hydroxy-4-methoxybenzophenone (HL ₃). The structures and optical properties of the Eu ^III complexes E1, E2 and E3 were characterized by elemental analysis, infrared/fluorescence spectroscopy and mass spectrometry. The aggregation-induced emission properties from E1, E2 and E3 were systematically investigated in the acetone/water binary mixtures. At the same time, the corresponding agglomeration behavior and self-assembly structures in the Eu ^III complex system was confirmed through scanning electron microscopy. Excellent luminescent performance was illustrated in sample of E1 (the luminescence quantum yield of 21.36 % in solid state) which should be attributed to the aggregation-induced emission from better self-assembly behavior with longer carbon chain in ligand. The results of ultraviolet aging resistance from E1 reveal that the self-assembly behavior could not only improve the aggregation-induced emission performance, but also enhance the photostability of Eu ^III complex compared with the traditional β-diketone Eu ^III complex. This discovery may provide a facile strategy to design and prepare more promising rare earth complexes with good luminescence properties and strong photostability for application in solid state.