Dual-response luminescent probe for Zn-based coordination polymers with sensitive detection of vitamin C and salicylic acid

Two Zn(II)-based coordination polymers (CPs), [Zn₃(L1)₂(Bpe)₂Cl₂]_n (1) and [Zn₂(L2)₂(Bpe)(H₂O)₂]_n (2) (Bpe = 1,2-bis(4-pyridyl)ethylene; H₂L1 = 4,4′-(1,2-phenylenebis(methyleneoxy))dibenzoic acid; H₂L2 = 3,5-bis(3′-carboxyphenyl)-1,2,4-triazole), were synthesized via solvothermal methods and subsequently characterized by FT-IR, powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and single-crystal X-ray diffraction. Crystallographic investigations reveal that the Zn(II) centres adopt distorted trigonal bipyramidal coordination environments. The resulting frameworks are constructed through the coordination of carboxylate groups in combination with N-donor Bpe linkers, leading to extended polymeric architectures. Both CPs display significant luminescence behavior and were further assessed as fluorescent probes for the detection of biomolecular species. Among the tested analytes, vitamin C (AA) induces significant fluorescence quenching with K_sv values of 4.80 × 10³ M⁻¹ for (1) and 1.73 × 10⁴ M⁻¹ for (2). The quenched systems further display turn-on fluorescence recovery toward salicylic acid, enabling a dual-response sensing system. Mechanistic investigations suggest that the fluorescence quenching predominantly arises from an inner filter effect (IFE)-dominated process.