Ratiometric Fluorescent Recognition of Sarin Simulant Enabled by a [Eu4(OH)4] Cluster-Based Metal–Organic Framework

Abstract

The rapid and sensitive detection of nerve agent simulants, such as diethyl chlorophosphate (DCP), is critical for public security and environmental monitoring. In this work, we report a novel europium metal–organic framework (SNNU-372) constructed from a cubane-type [Eu4(OH)4] cluster and a 2,5-diaminoterephthalate (2,5-(NH2)2-BDC). SNNU-372 exhibits a three-dimensional ecu topology with regular cages and uncoordinated amino groups lining the pore surfaces. The material serves as a ratiometric fluorescence sensor for DCP, showing a 65-fold emission enhancement at 492 nm upon addition of 20 ppm DCP, with a remarkable increase in the I492/I420 ratio from 0.5 to 7.0. The limit of detection (LOD) is as low as 0.01 ppm (49.9 nM), with fast response (100 s), excellent recyclability (≥5 cycles), and high selectivity against common interferents including HCl. Mechanistic studies reveal that DCP protonates the pendant −NH2 groups, suppressing ligand-to-metal charge transfer (LMCT) and intramolecular charge transfer (ICT), thereby turning on the ligand-centered fluorescence with a visible color change from nearly colorless to green under UV light.