Introduction of continuous excited-state intermolecular proton transfer process into open yttrium-terephthalate framework for ratiometric fluorescent fluorion detection

Highlights: • Unique continuous ESIPT processes in the confined channels of MOF. • Distinctive ratiometric fluorescent characteristics for fluorion detection. • Fast detection speed and good recyclability. • Strong anti-interference ability and high quantum yield. Fluorion detection has drawn great attention due to fluorides are usually toxicity but widely involved in chemical, industrial and biological processes. Considering the porosity of porous metal-organic framework (MOF) materials and fluoride ions may strongly influence the excited state intramolecular proton transfer (ESIPT) process, we propose that the introduction of ESIPT into MOFs should be promising for high-efficient fluorescence sensing of fluorions. In this work, the utilization of 2,5-dihydroxy terephthalic acid (DHBDC) with a pair of intramolecular hydrogen bonds as organic ligands led to a novel open yttrium-terephthalate framework (SNNU-300) as ESIPT-MOF fluorescence probe. Notably, the unique continuous ESIPT processes in the confined channels of SNNU-300 contribute a distinctive binate ratiometric fluorescent characteristics for fluoride ion detection. Quantitative fluorescence fluorion sensing experiments indicate SNNU-300 probe has high selectivity and sensitivity (K_sv=2.3×10⁴M⁻¹) and extra-low LOD value (1.2×10⁻⁶M). Also, fast detection, strong anti-interference ability and good reusability make SNNU-300 MOF a promising fluorion sensor in practical applications.