Metal-Organic Frameworks as Hosts for Fluorinated Azobenzenes: A Path towards Quantitative Photoswitching with Visible Light |
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Authors: | Dr. Daniela Hermann Dr. Heidi A. Schwartz Melanie Werker Prof. Dr. Dominik Schaniel Prof. Dr. Uwe Ruschewitz |
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Affiliation: | 1. Department of Chemistry, University of Cologne, Greinstraße 6, 50939 Köln, Germany;2. CRM2, Université de Lorraine & CNRS, 54506 Nancy, France |
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Abstract: | Fifteen new photochromic hybrid materials were synthesized by gas phase loading of fluorinated azobenzenes, namely ortho-tetrafluoroazobenzene (tF-AZB), 4H,4H′-octafluoroazobenzene (oF-AZB), and perfluoroazobenzene (pF-AZB), into the pores of the well-known metal-organic frameworks MOF-5, MIL-53(Al), MIL-53(Ga), MIL-68(Ga), and MIL-68(In). Their composition was analysed by elemental (CHNS) and DSC/TGA. For pF-AZB0.34@MIL-53(Al), a structural model based on high-resolution synchrotron powder diffraction data was developed and the host-guest and guest-guest interactions were elucidated from this model. These interactions of O−H⋅⋅⋅F and π⋅⋅⋅π type were confirmed by significant shifts of the O−H frequencies in loaded and unloaded MOFs of the MIL-53 and MIL-68 series. Most remarkably, all of the synthesized F-AZB@MOF systems can be switched with visible light, and some of them show almost quantitative (>95 %) photo-isomerization between its E and Z forms with no significant fatigue after repeated switching cycles. |
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Keywords: | azobenzene fluorinated derivatives metal-organic frameworks photochromism solid state switching |
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