Influence of aggregation behavior of Eu (III) complexes with phosphine oxide auxiliary ligands on their photophysical properties

Abstract

Based on thenoyltrifluoroacetone (TTA) as the anionic ligand, three europium(III) complexes Eu(TTA)₃(L1)₂ (E1), Eu(TTA)₃(L2)₂ (E2) and Eu(TTA)₃(L3)₂ (E3) were successfully synthesized by using different phosphine oxide auxiliary ligands: trioctylphosphin oxide(L1), triphenylphosphine oxide (L2), and trimethylphosphine oxide (L3). The structures and optical properties of E1, E2, and E3 were systematically characterized by elemental analysis, infrared spectroscopy, single-crystal Xray diffraction and fluorescence spectroscopy. It was found that E1 and E2 exhibited superior luminescence properties in aggregated state within an ethanol/water binary mixture, attributed to the self-assembly behavior induced by the long alkyl chain of L1 and the greater steric bulk of L2. Simultaneously, as compared with the classical complex Eu(TTA)₃phen (E4, phen=1,10-phenanthroline), scanning electron microscopy confirmed the characteristic structures of the Eu complexes in the ethanol-water mixed system. Subsequently, the ethanol-water mixed system and 1% doped PMMA (polymethyl methacrylate) films were prepared using the complexes, followed by UV aging tests. The results show that compared to E3 and E4, the uniquely structured ligands E1 and E2 not only enhanced the luminescence performance of Eu^III complexes in the aggregated state but also significantly improved the photostability of Eu^III complex materials. This research provides a potential strategy for designing and preparing rareearth complex materials that combine excellent luminescence properties with high photostability.