Smart Fluorescent Sensor: Gadolinium MOF for Highly Selective Detection of Explosives

Abstract

The development of highly sensitive and selective sensors for detecting high-energy materials (HEMs) is critical for national security and environmental monitoring. In this study, a fluorescent trivalent lanthanide metal–organic framework (MOF), Gd(DAB), was synthesized and systematically characterized for its ability to function as a turn-off photoluminescent sensor for nitro-based explosives. The structural and electronic properties of the MOF were investigated using spectroscopic and microscopic techniques, confirming its high stability, tunable luminescence, and strong metal–ligand interactions. Fluorescence quenching studies demonstrated that Gd(DAB) exhibits exceptional sensitivity toward electron-deficient explosives, particularly trinitrophenol (TNP) and trinitrotoluene (TNT), and other heterocyclic nitro-based explosives with Stern–Volmer (SV) analysis, indicating the highest quenching efficiency for nitroaromatics. Benesi–Hildebrand (BH) analysis further confirmed the formation of a ground-state charge-transfer complex with TNP, suggesting a static quenching mechanism at low quencher concentrations. At higher concentrations, a combination of static and dynamic quenching pathways was observed, as evidenced by fluorescence lifetime measurements. The mechanism of quenching was primarily attributed to electron transfer interactions between the electron-rich MOF and electron-deficient nitroaromatic compounds, effectively disrupting the ligand-to-metal charge transfer (LMCT) process and leading to fluorescence suppression. The findings establish Gd(DAB) as a highly efficient and selective luminescent sensor for HEM detection, offering a rapid, cost-effective, and sensitive approach for real-world applications in explosive sensing.