Isostructural Lanthanide Coordination Polymers with High Photoluminescent Quantum Yields by Effective Ligand Combination: Crystal Structures, Photophysical Characterizations, Biologically Relevant Molecular Sensing, and Anti-Counterfeiting Ink Application

Characteristically strong photoluminescence with high quantum yield and long emission lifetime plays vital roles for the sensing performance of functional lanthanide complexes. To enhance the energy transfer efficiency through the ligand-field effect, three lanthanide-based coordination polymers formulated as {[Ln(H2O)(TPA)(ox)]·0.5H2O}n (Ln-CPs, Ln = Eu, Tb, and Gd) were solvothermally synthesized via employing 6-(1H-1,2,4-triazol-1-yl)pyridine-2-carboxylate (TPA) and oxalate (ox) as antenna and bridging ligands. These obtained Ln-CPs were structurally and photophysically characterized, and the sensing capacity and feasible application of two luminescent Ln-CPs were further investigated. The three Ln-CPs are crystallographically isostructural, exhibiting (4 4) layers assembled from centrosymmetric {Ln2(TPA)2} dimers and pairs of ditopic ox2– linkages. Resulting from the conjugated TPA– chromophore and distorted LnIII coordination configuration, highly effective energy migration from the longer-lived triplet state of TPA– to LnIII is observed, endowing Eu-CP and Tb-CP to display bright red and green luminescence with an unexceptionable emission quantum yield up to 89% and 71%. Furthermore, the Tb-CP shows fast and effective responses toward the biomarkers of carcinoid cells with a strong Stern–Volmer quenching constant (KSV) and low detection limit (LOD) of 8.95 × 103 M–1 and 0.72 μM for 5-hydroxy tryptamine as well as 1.18 × 104 M–1 and 0.95 μM for 5-hydroxy-3-indoleacetic acid. Instead, the red-emitting Eu-CP can differentiate quercetin effectively with KSV = 1.82 × 104 M–1 and LOD = 0.58 μM. Furthermore, luminescent ink with strong anti-counterfeiting ability and long-term stability is developed, representing the promising practice of Ln-CPs as functional materials.