Light-induced switchable adsorption in azobenzene- and stilbene-based porous materials

Porous materials for gas storage and separations have had limited success in reaching working capacity goals because of fundamental limitations in how the gas is adsorbed within the microporous structures. Light-induced photoirradiation has distinct advantages over many other stimulus approaches, including being non-destructive, having high spatial and periodic resolution, and generating a more accurate and predictable response over the desired pressure range. The main strategies for light-induced switchable adsorption (LISA) are through the incorporation of photoresponsive molecules as guests (type 1), pendant groups (type 2), and backbones (type 3). Despite the relative infancy of the application of LISA to targeted gas storage and separations, preliminary research has shown promising advances, and we expect a diverse array of discoveries to be forthcoming in the next few years. Despite the long history of porous materials as adsorbates, fundamental limitations remain regarding the efficient capture and release of the gas molecules, with the working capacity of the material often overlooked. In microporous materials, the uptake is dominated by low-pressure adsorption, with much of this being at pressures below the minimum working threshold for many gas utilization processes. Thus, research has focused on several advances in porous materials, including photoresponsive organic units for light-induced switchable adsorption. This process utilizes light to trigger structural or electronic changes, alter the gas uptake, and change the working capacity. While a relatively recent development, there is a significant body of research regarding the use of light to control gas storage performance. Despite the long history of porous materials as adsorbates, fundamental limitations remain regarding the efficient capture and release of the gas molecules, with the working capacity of the material often overlooked. In microporous materials, the uptake is dominated by low-pressure adsorption, with much of this being at pressures below the minimum working threshold for many gas utilization processes. Thus, research has focused on several advances in porous materials, including photoresponsive organic units for light-induced switchable adsorption. This process utilizes light to trigger structural or electronic changes, alter the gas uptake, and change the working capacity. While a relatively recent development, there is a significant body of research regarding the use of light to control gas storage performance. two phenyl rings joined by two nitrogen atoms in an N–N double bond. The phenyl rings can also be functionalized with other functional groups. crystalline porous materials synthesized through covalent bonding of organic monomers, sometimes referred to as crystalline PPNs. electronic energy transfer from a ligand to a metal. a light-induced response that can result in switchable gas adsorption properties of a material. The reaction is often immediately reversible with the presence or absence of a photo trigger. a light-induced switchable catalytic state. crystalline porous materials comprising organic and inorganic components synthesized from ionic or coordination bonds. electronic energy transfer from a metal center to a ligand. also called MOPs; highly ordered porous materials maintaining their pore structures in solution. They are made from metal clusters and organic linkers like MOFs but are typically single pore units in size. thin films of porous materials constructed from polymers. These can have multiple phases or layers and can be made into composite materials with PCCs/MOPs, MOFs, or PPNs. also called POPs; non-crystalline porous materials synthesized from organic building blocks into a polymer matrix. two phenyl rings joined by two carbon atoms in a bridging C–C double bond. Also called the carbon analog of azobenzene.