Amino-functionalized europium-doped Zr-MOF as a ratiometric fluorescent probe for ultra-sensitive visual detection of trace water in organic solvents.

BACKGROUND: Trace water contamination in organic solvents severely hampers chemical synthesis, pharmaceutical manufacturing, and electronic device fabrication; however, existing detection methods lack portability, adequate sensitivity, or stability. While MOF-based fluorescent sensors show promise, most are limited by single-signal outputs, weak anti-interference capability, and poor solvent tolerance.

RESULTS: To address these challenges, we report an amino-functionalized europium-doped zirconium MOF (Eu@MOF-NH2), synthesized via a one-step solvothermal method, serving as a robust ratiometric fluorescent probe for trace water detection. The material exhibits dual emissions: ligand-based (435 nm) and Eu3+-centered (614 nm). Upon water exposure, strong hydrogen bonds with the ligand activate intramolecular charge transfer (ICT) to intensify the blue emission. Concurrently, high-frequency O-H vibrational coupling quenches the red emission by blocking ligand-to-metal energy transfer, causing a rapid (<30 s) pink-to-blue visual transition. The fluorescence intensity ratio (I435/I614) demonstrates excellent linearity with water content (0-10% v/v) and achieves ultralow limits of detection in ethanol (0.1643%), THF (0.0311%), methanol (0.3355%), and acetonitrile (0.0148%). Furthermore, this probe maintains consistent sensing performance across 11 diverse organic solvents with highly varying polarities. Integrated with a smartphone-assisted RGB colorimetric platform based on the blue-to-red intensity ratio, Eu@MOF-NH2 enables portable, on-site, and quantitative visual detection.

SIGNIFICANCE: This work overcomes the traditional limitations of sensitivity and stability, providing reliable material design and sensing strategies for industrial trace water monitoring and quality control.