The synthesis, characterization, and photophysical properties of two novel ligands, 5LIN(Me)-1,2-HOPO (1) and H(2,2)-1,2-HOPO (2), which utilize the 1,2-HOPO chelate as a sensitizer for Eu(III) are reported. In addition, the former ligand was structurally characterized as the Eu(III) complex by X-ray crystallography. The [Eu(1)(2)](-) complex of the tetradentate ligand (1) is stable in aqueous solution, to a limiting concentration of ca. 7 x 10(-9) M, and retains the superior photophysical performance noted for the 1,2-HOPO sensitizer. By contrast, the octadentate ligand (2) has vastly improved stability as the [Eu(2)](-) complex upon further dilution, to a limiting concentration of ca. 5 x 10(-17) M, which is beyond the minimum detectable concentration of most fluorimeters. The presence of a single coordinated water molecule for the latter complex reduces the overall metal-centered luminescence.