Photoresponsive Supramolecular Framework with Permanent Porosity for Controllable CO₂ Capture and Liberation

Supramolecular frameworks obtained via self-assembly of proper elementary building units have received great attention, as they can express advanced functions uneasily expressed by the elementary building units. Until now, the construction of supramolecular frameworks has remained a challenging task, not to mention photoresponsive supramolecular frameworks. Here, we report the first photoresponsive supramolecular framework (NUT-103) via hierarchical self-assembly of zirconium metal-organic cages containing trinuclear zirconium clusters and azobenzene-functionalized ligands. NUT-103 displays permanent porosity and reversible photoresponsive properties. Photoregulating adsorption of CO₂ was realized for NUT-103 and the regulation efficiency can reach 55%, while that of CH₄ and N₂ is only 7% and 3%, respectively. Grand Canonical Monte Carlo simulations demonstrate that the photoregulation property of NUT-103 is attributed to the variation of adsorption capacity in the interstitial region of adjacent cages. Moreover, NUT-103 can be dissolved to form discrete metal-organic cages and can be recovered by simple recrystallization. The recovered NUT-103 displays similar adsorption and photoresponsive behavior as the fresh sample.