Exactly Restricting the Phenyl Ring Rotation in Metal-Organic Framework for Ultra-Sensitive and Specific Ratiometric Fluorescent Sensing of Sarin

Abstract

To realize highly sensitive and specific sensing toward sarin, an Eu(III) based metal-organic framework (Eu-CTTB-MOF), encompassing a π-conjugated organic ligand H₄CTTB (4,4′,4″,4‴-(9H-carbazole-1,3,6,8-tetrayl)tetrabenzoic acid) was explored for ratiometric fluorescent sensing. An unprecedented specific recognition of nerve-agent sarin mimic diethyl chlorophosphate (DCP) in the presence of HCl interferent and a low limit of detection (LOD, 20.97 nM) were achieved. This excellent detection performance is driven by the dual hydrogen bonding and hydrophobic interaction between the CTTB organic ligand and DCP, which would cause a dramatic change in the molecular configuration of the CTTB ligand. Density functional theory (DFT) calculations further verify the recognition of DCP by Eu-CTTB-MOF could suppress the rotations of the aromatic rings in CTTB ligand, significantly reducing the nonradiative decay pathways and subsequently enhancing the fluorescent intensity of the CTTB ligand. Especially, the Eu-CTTB-MOF enables the immediate response to DCP vapor and excellent specificity towards DCP even in the presence of 18 types of interferents, including HCl vapor, structural analogs, and volatile organic solvent, and a gas detector with accurate detection of DCP in simulated scenarios, positioning the designed MOF as a promising sensing material for practical scenarios. We expect that the present sensing strategy will shine a light on the development of brand-new sensing materials for on-site detection applications.