The Fluorescent Sensors Based On Lanthanide Eu(Ⅲ)

Luminescence from rare earth ions is a promising tool in optical imaging and sensing of biological systems. Due to their unique photophysical properties, such as the long-life excited states, the long wavelength emission (occurring in the NIR or in the visible), and sharp line-like emission bands. Long wavelength emission can overcome light scattering and autofluorescence from biological backgrounds. The traditional organic fluorophores have not these properties. Europium ion lain in an asymmetric coordinate site can emit strong red fluorescence in visible region at613nm, corresponding to5D0�'7F2transition. Simultaneously, this band belongs to ultrasensitive transition, which is sensitive to the surrounding. We can identify the target substrate based on the property of europium ion. Usually, the coordination number of europium ion is9-11. Phenanthroline and derivatives have stronger light absorption abilities, and have been proved that the energy level of the triplet state is matched to the energy level of the excited state of europium ion. So the fluorescence intensity of europium complex can be enhanced. Based on the carboxyl substituted phenanthroline derivatives as "antenna" and ligand molecules, the article synthesizes a series of coordinatively unsaturated europium complexes. The design is based on the luminescence quenching of the coordinated water moleculeses and the stronger coordination ability of Eu3+with oxygen atom than nitrogen atom. When a target substrate exists, the target substrate will replace water molecules or nitrogen-coordinated ligands and lead to the change of ultrasensitive transition intensity of europium ion.In this article, we synthesize three europium complexes based on phenanthroline and its derivatives, which can be used to identify Fe3+and phosphate anion, respectively. The contents are listed in detail as following:1. A novel Eu3+complex (EuL) based on1,10-phenanthroline-2-carboxylic was successfully synthesized, and gave a characteristic red emission. The complex was shown to act as a selective luminescence quencher for Fe3+, as shown by the "on/off" switch phenomenon. The quenching curve showed a double-exponential well decay with the increase of Fe3+ions. The stability constant of EuL/Fe3+was calculated as8.6*103=3.93). The response showed high selectivity for Fe3+compared with other metal ions; the complex therefore has the potential to be applied as a fluorescent sensor for Fe3+.2. A coordinatively unsaturated europium complex EuL1L2was synthetized and characterized based on1,10-phenanthroline, and8-hydroxyquinoline. The complex can detect phosphate. The complex emits weak fluorescence in DMSO-water (V:V,5:1). Maybe the vibration from the hydroxyl group of water coordinated with Eu3+quenches the luminescence. After addition of phosphate, the phosphate ion replaces the water molecule and prohibits the non-radiative quenching. The luminescence of the europium complex recovered. With the increase of phosphorate, the emission intensity of the system increased gradually. When the concentration of phosphorate is in5eq to EuL1L2, fluorescence intensity at520nm shows a linear correlation to the concentration of phosphate. With further increase of the concentration of phosphate, fluorescence intensity at520nm increased sharply. Maybe phosphate ion replaces8-hydroxyquinoline coordinated with europium ion, and8-hydroxyquinoline ligand is released. The solution emits a strong yellow fluorescence from8-hydroxyquinoline.3. A coordinatively unsaturated europium complex EuL3L4was synthetized and characterized based on one N-oxided2,9-dicarboxyl phenanthroline and two acetate ligands. The coordination reaches saturation by combining solvent molecules. The complex can detect phosphate ions in pure water. Fluorescence of the complex was quenched by O-H vibration. The addition of PO43-、HPO42-or H2PO4-can recover the red-color fluorescence. The detection was not interfered by other anion. The binding constants between the complex and phosphate is2×105M-1with the form of1:1adduct.