New 2,5-di-4-pyridinylphenol appended Cd(II)-based coordination polymer: Photoluminescent sensing of isoliquiritigenin from dendrobium

A new luminescent cadmium(II)-based coordination polymer, [Cd(OAc)₂(DPP)] (1), was synthesized hydrothermally using 2,5-di(4-pyridyl)phenol (DPP) and Cd(CH₃COO)₂·2H₂O. The structure of 1 was elucidated through single-crystal X-ray diffraction and further supported by FT-IR, PXRD, TGA, SEM, and XPS analyses. It features a two-dimensional layered network with Cd(II) centers in a pentagonal bipyramidal geometry, stabilized by O–H···O hydrogen bonding and π–π stacking. The acetate ligands adopt μ₁-η¹:η¹ and μ₂-η¹:η¹ coordination modes. Owing to its strong luminescence, 1 was investigated as a fluorescence sensor for bioactive molecules derived from Dendrobium species. Among the tested analytes, isoliquiritigenin (Is) caused pronounced fluorescence quenching (“turn-off”), while salicylic acid (SA) induced enhancement (“turn-on”). The sensor exhibited high sensitivity with a detection limit of 1.853 × 10⁻⁴ mol/L for Is and excellent recovery (95.6–100.4 %) in real water samples. These results demonstrate that 1 is a promising, selective, and reusable luminescent sensor for environmental and bioanalytical applications.