Preparation of Eu(III) Complexes Containing Maleopimaric Acid Anhydride with Ultra-narrow and Efficient Fluorescence Emission for High Determination on Gallic Acid in Acetonitrile Solution.

Two novel Eu(III) complexes constructed by maleopimaric acid anhydride (MPA) and 2,2'-bipyridyl (Bpy) / 1, 10-phenanthroline (Phen), named as MPA-Bpy-Eu / MPA-Phen-Eu, have been synthesized by a one-step precipitation method. FTIR, UV, TG, elemental analysis, XPS, and ESI-MS revealed the successful coordination of Eu(III) ions with MPA and Bpy / Phen through Eu-O and Eu-N bonds, respectively. Introducing MPA into coordinate structure increased the electron cloud density in 3d5/2 orbit of Eu(III) ions, enhanced the absolute quantum yields of MPA-Bpy-Eu (89.27%) and MPA-Phen-Eu (94.41%), and decreased the full width at half maxima of 5D0 → 7F2 transitions of MPA-Bpy-Eu (2.23 nm) and MPA-Phen-Eu (2.93 nm), respectively. The fluorescence quenching experiments showed that there was a good linear relationship between the relative fluorescence intensity of MPA-Bpy-Eu and gallic acid (GA) concentration in acetonitrile solution in the range of 0 to 8.41 × 10-2 mM. The results of UV-vis spectra, the fluorescence lifetimes, and the quantum yields demonstrated that the dynamic quenching model played a major role in the quenching process of GA on MPA-Bpy-Eu. The quenching process of GA on MPA-Phen-Eu involved dual fluorescence quenching mechanistic pathways, including static and dynamic models.