Triple-Emission Lanthanide Metal−Organic Framework for Crosstalk-Free and Dual-Ratiometric Simultaneous Sensing of Copper(II) and Nitrite

Abstract Copper ions (Cu2+) and nitrite (NO2−) are two prevalent pollutants in aquatic environments that frequently coexist and potentially exert synergistic toxic effects. However, the simultaneous and precise quantification of these two species remains a formidable challenge due to signal interference. In this study, a triple-emission lanthanide metal−organic framework (Ln-MOF) ratiometric fluorescent probe, Eu/Tb-BDC/BDC-NH2, was engineered via a dual-ligand and dual-lanthanide strategy. Under a single excitation wavelength (260 nm), the probe exhibits three independent and orthogonal emission signals at 433, 544, and 695 nm, originating from the BDC-NH2-related emission, Tb3+, and Eu3+, respectively. Unlike conventional sensors, Cu2+ and NO2− selectively quench the fluorescence at 433 and 544 nm (F433 and F544), respectively, while the 695 nm emission (F695) remains essentially stable as a reliable internal reference. By integrating two ratiometric sensing channels (F433/F695 and F544/F695), this platform enables the simultaneous detection of Cu2+ and NO2− within a single sensing system. The system demonstrates a rapid response (30 s), low detection limits, and reliable performance in practical water analysis. This work not only provides a novel paradigm for designing multi-emission Ln-MOFs but also offers new insights into the simultaneous analysis of multiple pollutants in complex environmental samples.