Alkaline-earth phosphonate MOFs with reversible hydration-dependent fluorescence

Area of Science:

• Materials Science
• Inorganic Chemistry
• Supramolecular Chemistry

Background:

• Metal-organic frameworks (MOFs) offer tunable properties for various applications.
• Phosphonate ligands are versatile building blocks for MOF synthesis.
• Luminescent MOFs are of interest for sensing and optical devices.

Purpose of the Study:

• To synthesize a novel tritopic phosphonic ligand.
• To construct isostructural barium and strontium phosphonate MOFs.
• To investigate the water-dependent fluorescence properties of the resulting MOFs.

Main Methods:

• Synthesis of 2,4,6-tris(4-phosphonophenyl)pyridine (H6L) ligand.
• Hydrothermal assembly of barium (1) and strontium (2) MOFs.
• Room temperature fluorescence spectroscopy to study water-induced changes.

Main Results:

• Successful synthesis of the rigid tritopic phosphonic ligand H6L.
• Formation of isostructural barium and strontium phosphonate MOFs.
• Observation of fully reversible and selective fluorescence red-shift upon water adsorption/desorption at room temperature.

Conclusions:

• The new ligand H6L enables the construction of functional phosphonate MOFs.
• The MOFs exhibit unique water-responsive luminescence, suggesting potential for humidity sensing.
• The structural and luminescent properties are tunable by metal ion choice (Ba vs. Sr).