Two heterometallic MOFs fluorescence probes: Their syntheses, structures, and sensing properties

Based on a 2-(2,6-bis(pyrazine-2-yl)pyridine-4-yl) benzene-1,3,5-tricarboxylic acid ligand (H₃pbta), two isomorphic d-f heterometallic organic frameworks with porous three-dimensional structures were successfully synthesized, namely, {[LnCd₂(pbta)₂Cl(H₂O)₄](H₂O)₄}_n(1, Ln = Eu; 2, Ln = Tb). The experimental results indicated that complex 1 and 2 exhibited stable luminescence in a wide range of in aqueous solution. Notably, complex 1 could recognize palmatine (PMT) in simulated human urine and complex 2 was able to distinguish tartrazine (TAR) in some food additives. It was worth pointing out that complex 1 and 2 displayed high selectivity, recoverability, anti-interference, and low detection limits for the identification of PMT and TAR in aqueous solution, respectively. In addition, the fluorescence mechanisms for the detection of PMT and TAR were elucidated in detail by the corresponding experiments and theoretical calculations. Also, the fluorescent sensing films based upon complex 1 and 2 were fabricated to visually discern PMT and TAR for their practical applications, respectively.