Introduction of Lewis acidic and redox-active sites into a porous framework for ammonia capture with visual color response

Based on the Lewis acidic site and redox ability of bipyridinium ligand, a porous framework with an adsorption advantage for ammonia over water and color response ability has been constructed. The compound is highly stable and flexible to external stimuli, exhibiting reversible single-crystal-to-single-crystal transformations, in response to temperature change and NH₃ capture. More attractively, the title compound shows obvious color change from yellow to dark blue when exposed to ammonia vapor within just a few seconds, indicating a strong ability to function as a visual colorimetric absorbent for ammonia.