Viologen-Based Photochromic Metal–Organic Framework for Antibiotics Detection in Water

A viologen-functionalized europium-based metal–organic framework, denoted as compound 1, has been synthesized solvothermally by employing 1,1′-bis(3,5-dicarboxyphenyl)-4,4′-bipyridinium dichloride (abbreviated as H4bdcbpCl2). Compound 1 possesses a 2-fold parallel self-interpenetrating structure composed of two sets of identical three-dimensional (3D) cationic frameworks with {4·84·12}2{42·82·102}{8}2 topology. The introduction of tetracarboxylic group-decorated viologen derivative not only facilitates the formation of a helix-based structure with high dimensionality and positively charged framework but also promotes the photoinduced electron transfer (PET)-caused photochromic property. Significantly, compound 1 demonstrates a rapid detection process for nitrofurantoin (NFT) and nitrofurazone (NFZ) in aqueous environments, exhibiting good recycling stability, large quenching coefficient (Ksv), low limit of detection (LOD), and high anti-interference ability through a fluorescence turn-off mechanism. This phenomenon was further investigated through spectroscopic analyses and density functional theory (DFT) calculations. Moreover, compound 1 also exhibits sensing capabilities for various ions in aqueous system, including Fe3+, Cr2O72–, and MnO4–, which further verify that compound 1 could serve as a multifunctional fluorescence sensor for molecular and ionic pollutants.