Four Novel Lanthanide(III) Metal–Organic Frameworks: Tunable Light Emission and Multiresponsive Luminescence Sensors for Vitamin B6 and Pesticides

Four novel lanthanide(III)-based metal–organic frameworks (MOFs), formulated as [Ln 3 (HDDB)(DDB)(H 2 O) 6 ]·NMP·3H 2 O (Ln = Eu ( 1 ), Tb ( 2 ), Dy ( 3 ), Gd ( 4 )), were successfully constructed with a rigid pentacarboxylate ligand 3,5-di(2′,4′-dicarboxylphenyl) benzoic acid (H 5 DDB). Complexes 1 – 4 are isostructural and exhibit a new 3,4,4,6-connected network. 1 – 2 exhibit excellent fluorescence properties and good water stability. The emissions of the doped bimetallic Eu x Tb 1– x -MOFs can be adjusted by varying the Eu(III)/Tb(III) ratios used in the reaction. Furthermore, 2 presents excellent sensitivity and selectivity to sense vitamin B 6 (VB 6 ) and the pesticide 2,6-dichloro-4-nitroaniline (DCN) as a multiresponsive luminescent sensor. Compound 2 is the first MOF-based luminescent sensor for detecting VB 6 with a low detection limit (LOD) of 9.5 × 10 –8 M (∼58.4 ppb) in phosphate buffer solution (pH = 6.86), which also displays a high-sensitivity sensing activity for VB 6 in human serum. Moreover, 2 exhibits high-sensitivity sensing for the pesticide DCN with an LOD value of 1.4 × 10 –7 M (∼86.1 ppb) in aqueous solution, and it also can be successfully used for detecting DCN in the extracts of carrots, grapes, and nectarines.