Three robust Cd(ii) coordination polymers as bifunctional luminescent probes for efficient detection of pefloxacin and Cr₂O₇^2- in water

The accurate and rapid detection of antibiotics and heavy-metal-based toxic oxo-anions in water media employing coordination polymers (CPs) as luminescent probes has attracted a lot of attention. Three new Cd(II)-based ternary CPs derived from first-presented L ligands, including [Cd(DCTP)(L)(OH)](n) (1), [Cd(TBTA)(L)(OH)](n) (2), and [Cd(NPHT)(L)(H2O)](n) (3) (L = 2-((1H-imidazol-1-yl)methyl)-5,6-dimethyl-1H-benzo[d]imidazole, H2DCTP = 2,5-dichloroterephthalic acid, H(2)TBTA = tetrabromoterephthalic acid and H2NPHT = 3-nitrophthalic acid), were successfully assembled and characterized. 1 and 2 show 2D hcb layers, which can be further extended into a 3D supramolecular framework via classic hydrogen bonding interactions. 3 features a 1D double chain that ultimately spreads into a 2D network through weak hydrogen bonding interactions. With the advantages of high stability and excellent luminescent properties, the three CPs display high sensitivity, selectivity, and good anti-interference for the sensing of pefloxacin (PEF) and Cr2O72- ions (LOD values toward PEF: 3.82 x 10(-7) mol L-1 for 1, 4.06 x 10(-7) mol L-1 for 2, and 1.36 x 10(-8) mol L-1 for 3, and toward Cr2O72- ions: 5.97 x 10(-7) mol L-1 for 1, 5.87 x 10(-7) mol L-1 for 2, and 8.21 x 10(-8) mol L-1 for 3). These CPs are the first examples of bifunctional luminescent sensors to detect PEF and Cr2O72- in aqueous solutions. The luminescence quenching mechanisms are explored in detail.