Dual-Function Fluorescence Sensors Based on Interpenetrated Isomeric Cd-MOFs: Selective Detection of 2,4,6-Trinitrophenol and Nitrofurazone

This work addresses the detection of nitroaromatic compounds (NACs) and antibiotics in water by developing two isomeric fluorescent metal-organic framework (MOFs) Cd-1 and Cd-2, with the formula [Cd2(Tipe)(ABD)2]·solvent (Tipe = 1,1,2,2-tetrakis(4-(1-imidazolyl)phenyl)ethylene, H2ABD = 4,4'-azodibenzoic acid). By modulating the reaction solvent, two interpenetrated isomeric MOFs with distinct space groups and fluorescence properties were obtained. Interestingly, Cd-1 and Cd-2 exhibit high selectivity and rapid response (<10 s) toward 2,4,6-trinitrophenol (TNP) and nitrofurazone (NFZ) with distinct response behaviors. Namely, Cd-1 shows fluorescence quenching at both 423 and 485 nm, whereas Cd-2 exhibits quenching only at 423 nm but remains unchanged at 485 nm, implying a ratiometric fluorescence sensor (I423/I485). Both Cd-1 and Cd-2 possess low detection limits (0.32 and 0.24 μM for TNP and 0.34 and 0.15 μM for NFZ), strong anti-interference ability, good reusability, and structural stability. Spectroscopic overlapping and fluorescence lifetime shortening imply a dynamic quenching mechanism. X-ray photoelectron spectroscopy (XPS) analysis further suggests electron transfer from the MOF skeleton to analytes of TNP/NFZ. This study provides an example of solvent-regulated interpenetration isomerism in MOFs, reveals its modulatory role in fluorescence response behaviors, and offers new insights for designing ratiometric fluorescence sensors.