Metal-Organic Frameworks with Target-Specific Active Sites Switched by Photoresponsive Motifs: Efficient Adsorbents for Tailorable CO Capture.

Photoresponsive metal-organic frameworks (PMOFs) are of interest for tailorable CO adsorption. However, modulation of CO adsorption on PMOFs is based on steric hindrance or structural change owing to weak interactions between CO and active sites. It is challenging to fabricate PMOFs with strong but tailorable sites for CO adsorption. Now, the construction of PMOFs with target-specific (strong) active sites is achieved by introducing tetraethylenepentamine into azobenzene-functionalized MOFs for tailorable CO adsorption. Amines are specific active sites for CO , contributing to capture CO selectively. Cis/trans isomerization of azobenzene motifs trigged by UV/Vis light adjusts the electrostatic potential of amines significantly, leading to exposure/shelter of amines and modulation of CO adsorption on strong active sites. This system enables us to design adsorption processes for CO capture from mixtures, which is impossible to realize by traditional PMOFs.