Structural Effects in Visible-Light-Responsive Metal-Organic Frameworks Incorporating ortho-Fluoroazobenzenes

• Published in: Chemistry : a European journal 2016-01, Vol.22 (2), p.746-752
• Main Authors: Castellanos, Sonia, Goulet-Hanssens, Alexis, Zhao, Fangli, Dikhtiarenko, Alla, Pustovarenko, Alexey, Hecht, Stefan, Gascon, Jorge, Kapteijn, Freek, Bléger, David
• Format: Article
• Language: English
• Subjects: Adsorption; Adsorptivity; Aluminum; azo compounds; Bearing; Carbon dioxide; carboxylate ligands; Catalysis; Channels; Chemistry; Construction materials; Conversion; Heat; Irradiation; Isomerization; Jewelry; Low energy; Materials selection; Metal-organic frameworks; Metalorganic compounds; Metals; Nodes; Penetration depth; photochromism; Photons; photoswitches; Radiation damage; Reflectance; Separation; Spectroscopic analysis; Spectroscopy; Stability; Ultraviolet radiation; Voids
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201503503

The ability to control the interplay of materials with low‐energy photons is important as visible light offers several appealing features compared to ultraviolet radiation (less damaging, more selective, predominant in the solar spectrum, possibility to increase the penetration depth). Two different metal–organic frameworks (MOFs) were synthesized from the same linker bearing all‐visible ortho‐fluoroazobenzene photoswitches as pendant groups. The MOFs exhibit different architectures that strongly influence the ability of the azobenzenes to isomerize inside the voids. The framework built with Al‐based nodes has congested 1D channels that preclude efficient isomerization. As a result, local light–heat conversion can be used to alter the CO2 adsorption capacity of the material on exposure to green light. The second framework, built with Zr nodes, provides enough room for the photoswitches to isomerize, which leads to a unique bistable photochromic MOF that readily responds to blue and green light. The superiority of green over UV irradiation was additionally demonstrated by reflectance spectroscopy and analysis of digested samples. This material offers promising perspectives for liquid‐phase applications such as light‐controlled catalysis and adsorptive separation. Photo‐MOFs respond to green and blue: Incorporating all‐visible azobenzene photoswitches into microporous metal–organic frameworks (MOFs) confer good photochromic properties and the ability to photomodulate CO2 uptake on irradiation with visible light. The influence of the structures of the MOFs on the photoswitching ability of confined fluoroazobenzene moieties was investigated (see figure).