Two Novel Viologen-Based Metal–Organic Frameworks: Syntheses, Structures and Properties in Inkless Printing and Antibiotics Detection

Two novel viologen-based yttrium metal–organic frameworks, Y4(H2bcbp)(bcbp)(μ2-C2O4)6(H2O)2Cl2·4H2O (1) and Y2(bcbp)(μ2-C2O4)2(NO3)2·H2O (2), were solvothermally synthesized and characterized. Compound 1 displays a three-dimensional (3D) structure with a dia (sqc-6) topology based on (6,3)-hcb yttrium-oxalate layers. Compound 2 displays a 3D structure with a 2-fold interpenetrating mog topology based on yttrium-oxalate chains. Both compounds possess photochromic behaviors induced by photoinduced electron transfer (PET) generating viologen radicals, as confirmed by UV–vis and EPR spectroscopy. Based on these properties, compound 1 is utilized in inkless and erasable printing. Furthermore, compound 1 can serve as a highly sensitive and selective fluorescence sensor for nitrofuran antibiotics (NFZ and NFT) in aqueous systems, with low detection limits LODs (2.11 × 10–7 M for NFZ and 1.56 × 10–7 M for NFT), high quenching coefficients KSV (5.43 × 104 M–1 for NFZ and 3.82 × 104 M–1 for NFT), and excellent selectivity and recyclability. The quenching mechanism is attributed to a synergistic effect of the inner filter effect (IFE), fluorescence resonance energy transfer (FRET), and PET. This work highlights the potential of viologen-based MOFs in smart materials and environmental monitoring.