Luminescent metal–organic frameworks (LMOFs) as sensors showing highly efficient detection toward toxic heavy-metal ions are in high demand for human health and environmental protection. A novel nanocage-based N-rich LMOF (LCU-103) has been constructed and characterized. It is a 2-fold interpenetrating structure built from N-rich {Zn6(dttz)4} nanocages extended by N-donor ligand Hdpa [H3dttz = 4,5-di­(1H-tetrazol-5-yl)-2H-1,2,3-triazole; Hdpa = 4,4′-dipyridylamine]. Notably, LCU-103 contains abundant N functional sites anchoring on both the windows of nanocages and the inner channels of the framework that can interact with metal ions and then recognize them. As a result, it can serve as a luminescent sensing material for detecting trace amounts of Fe3+ and Cu2+ ions with low limits of detection (LODs) of 1.45 and 1.66 μM, respectively, through a luminescent quenching mechanism. Meanwhile, LCU-103 as a LMOF sensor exhibits several advantages such as high sensitivity, appropriate selectivity (for Fe3+ in H2O), recycling stability, and fast response times in N,N-dimethylformamide. Moreover, LCU-103 also displays good luminescent quenching activity toward Fe3+ in H2O and a simulated 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid biological system with low LODs of 1.51 and 1.52 μM, respectively. LCU-103 test papers were further prepared to offer easy and real-time detection of Fe3+ and Cu2+ ions. Importantly, when density functional theory calculations and multiple experimental evidence, including X-ray photoelectron spectroscopy, UV–vis absorption, luminescence decay lifetimes, and quantum efficiencies, are combined, a preferred N-donor site and possible weak interaction sensing mechanism is also proposed to elucidate the quenching effect.

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Two Zn-MOFs, namely, {[Zn(L) 0.5 (bpea)]•0.5H 2 O• 0.5DMF} n [LCU-113 (for Liaocheng University)] and {[Zn-(L) 0.5 (ibpt)]•H 2 O•DMF} n (LCU-114), were synthesized based on flexible tetracarboxylic acid 1,3-bis(3,5-dicarboxyphenoxy)benzene (H 4 L) and different N-ligands [bpea = 1,2-dipyridyl ethane; ibpt = 3-(4′imidazolobenzene)-5-(pyridine-4′-yl)-1,2,4-triazole].LCU-113 and LCU-114 possess twofold interpenetrating three-dimensional pillared layer structures, in which a two-dimensional layer formed by carboxylic acid and Zn 2+ ions was pillared by bpea and ibpt, respectively. The two complexes show high water stability and high luminescence sensing performance toward organic solvents, ions, and antibiotics, as well as chemicals, in simulated urine. The investigation showed that (1) LCU-113 and LCU-114 could detect uric acid (UA, 2,6,8-trihydroxypurine, metabolite of purine) and p-aminophenol (PAP, biomarker of phenamine) in simulated urine by luminescence quenching, respectively, and (2) luminescence quenching of LCU-113 and LCU-114 occurred in aqueous solutions of nitrofurazone (NZF), Fe 3+ , and CrO 4 2− /Cr 2 O 7 2− . All the above detections have excellent anti-interference ability and recyclability. The luminescence mechanism analysis indicates that weak interactions between the framework structures and the target analytes as well as the energy competition (inner filter effect) play an important role in sensing the above analytes. The practical application for monitoring NZF/Fe 3+ in water samples was also tested.