Amino-Induced Microenvironment Modulation in Eu-MOFs Enabling Ratiometric Fluorescence Sensing of Sarin and Mustard Gas Simulants

The development of promising technology capable of detecting chemical warfare agents (CWAs) in real time, rapidly, and with high sensitivity is of vital significance to global public security. This work systematically demonstrated how amino functionalization modulated the pore microenvironments of europium-based metal-organic frameworks (Eu-MOFs, SNNU-369/-370/-371) and further enabled simultaneous ratiometric fluorescence detection for sarin and mustard gas simulants (diethyl chlorophosphite (DCP) and 2-chloroethyl ethyl sulfide (CEES)). Keeping similar pore structures, SNNU-369 without amino groups showed no significant response to DCP and CEES. In contrast, SNNU-370 and SNNU-371 decorated with one or two amino groups on the pore surface showed highly selective ratiometric fluorescence detection ability for the sarin or mustard gas simulants via amino protonation (for DCP) and hydrogen-bonding interactions (for CEES). The limits of detection (LOD) of SNNU-370 for DCP and CEES were determined to be 1 ppb and 1.5 ppm, respectively, and those values of SNNU-371 were 0.3 ppm for DCP and 0.4 ppm for CEES. At the same time, both MOF probes exhibited fast response (≤120 s), good cycling stability, and excellent anti-interference capability. A further mechanism study indicated that the interactions between amino groups and analytes suppressed internal charge transfer (ICT), ligand-to-metal charge transfer (LMCT), and nonradiative transitions, leading to a significant enhancement of ligand-centered emission accompanied by distinct color changes (SNNU-370: red → blue; SNNU-371: light blue → yellowish-green) and thus activated the ratiometric fluorescence response. This work not only developed a unique bifunctional fluorescence sensing MOF platform for sarin and mustard gas simulants but also provided important insights for the rational design of high-performance detection materials at the molecular level.