A blue-emitting porous MOF incorporated with red-emitting Eu(III) ions for nitro compounds fluorescence sensing: Improving ratiometric selectivity and sensitivity by synergistic effect of a dendritic auxiliary ligand

Due to the high nitrogen oxidation valence and electron-deficient structure, organic nitro compounds are generally known as potential explosive which are also considered as environmental threat. Optical sensing is an attractive quantification method with simple operation procedure and limited requirement for equipment, but traditional optical sensing platforms for nitro compounds suffered from limited sensitivity and poor selectivity. To solve this problem, this work designed applied a ratiometric sensing platform. Here red-emitting Eu(III) was incorporated into a blue-emitting host bio-MOF-1. A dendritic auxiliary ligand (denoted as BBB) was adopted to stabilize the adduct between Eu(III) and TPA (2,4,6-trinitrophenol). By so doing, the blue emission intensity from bio-MOF-1 was increased, while the Eu3+ emission intensity was minimized. The sensing behavior upon auxiliary ligand BBB was compared to that upon a reference ligand (1,10-phenanthroline). The sensing mechanism was proved as an irreversible Eu(III) leak and coordination with TPA/BBB guaranteed by BBB steric hindrance. Finally, a linear working equation with improved sensitivity (by sixfold) and unique selectivity was observed.