Conformation Regulation of Perylene Diimide Derivatives by Lanthanide Coordination for Turn-On Fluorescence Sensing of Sarin Simulants

Fluorescent metal-organic frameworks (MOFs) are promising sensing materials that have received much attention in recent years, in which the organic ligand conformation changes usually lead to variations of their sensing behavior. Based on this, in the present work, perylene diimide (PDI) derivatives with excellent photochemical properties closely related to their conformation and molecule packing fashion were selected as organic linkers to detect sarin simulant diethyl chlorophosphate (DCP). By the coordination interactions with large lanthanide cations through terminal carboxylate groups from the PDI derivative, a series of one-dimensional coordination polymers, named [Ln(PDICl₄-2COO)(μ₂-O)_0.5(DMF)_1.5] (SNNU-112, Ln = Yb/Tb/Sm/Nd/Pr/Gd/Eu/Er/Ce, PDICl₄-2COOH = N,N'-bis(4-benzoic acid)-1,2,6,7-tetrachlorohydrazone-3,4,9,10-tetracarboxylic acid diimide) were synthesized. Regulated by the coordination process, the ligand undergoes a certain degree of conformational turnover and thus leads to an electron distribution change compared to free PDICl₄-2COOH. Notably, the contact with the DCP molecule triggered a further ligand conformational conversion of PDI ligands in SNNU-112 and thus caused a fluorescence turn-on phenomenon realizing a well-defined fluorescence detection performance for DCP on the basis of a photoinduced electron transfer process. Among nine lanthanide MOFs, Yb-MOF sensor exhibited the lowest detection limit (4.36 ppb), fast response, high selectivity, and good recyclability. Such molecular conformation regulation of PDI derivatives by metal coordination may provide a new way for the exploration of fluorescent sensors.