TY - JOUR A1 - Mutruc, D. A1 - Goulet-Hanssens, A. A1 - Fairmann, S. A1 - Wahl, S. A1 - Zimathies, Annett A1 - Knie, C. A1 - Hecht, S. T1 - Modulating Guest Uptake in Core-Shell MOFs with Visible Light JF - Angewandte Chemie N2 - A two-component core-shell UiO-68 type metal-organic framework (MOF) with a nonfunctionalized interior for efficient guest uptake and storage and a thin light-responsive outer shell was prepared by initial solvothermal MOF synthesis followed by solvent-assisted linker exchange. The bulky shell linker features two tetra-ortho-fluorinated azobenzene moieties to exploit their advantageous photoisomerization properties. The obtained perfect octahedral MOF single crystals can be switched repeatedly and with an unprecedented efficiency between E- and Z-rich states using visible light only. Due to the high photoswitch density per pore of the shell layer, its steric demand and thus molecular uptake (and release) can be conveniently modulated upon green and blue light irradiation. Therefore, the "smart" shell acts as a light-controlled kinetic barrier or "gate" for the diffusion of cargo molecules in and out of the MOF crystals. KW - Visible light KW - Azobenzene KW - Guest uptake/release KW - Metal– organic frameworks KW - Photochromism PY - 2019 DO - https://doi.org/10.1002/anie.201906606 VL - 58 SP - 12862 EP - 12867 PB - WILEY-VCH Verlag GmbH & Co. KGaA CY - Weinheim AN - OPUS4-48941 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kowarik, Stefan A1 - Weber, C. A1 - Pithan, L. A1 - Zykov, A. A1 - Bommel, S. A1 - Carla, F. A1 - Felici, R. A1 - Knie, C. A1 - Bléger, D. T1 - Multiple timescales in the photoswitching kinetics of crystalline thin films of azobenzene-trimers JF - Journal of Physics: Condensed Matter N2 - Functional materials that exhibit photoinduced structural phase transitions are highly interesting for applications in optomechanics and mechanochemistry. It is, however, still not fully understood how photochemical reactions, which are often accompanied by molecular motion, proceed in confined and crystalline environments. Here we show that thin films of azobenzene trimers exhibit high structural order and determine the crystallographic unit cell. We demonstrate that thin film can be switched partially reversibly between a crystalline and an amorphous phase. The time constant of the photoinduced amorphisation as measured with real-time x-ray diffraction ($\approx $ 220 s) lies between the two time constants (120 s and 2870 s) of the ensemble photoisomerisation processes that are measured via optical spectroscopy. Our observation of a photoinduced shrinking of the crystalline domains indicates a cascading process, in which photoisomerisation starts at the surface of the thin film and propagates deeper into the crystalline layer by introducing disorder and generating free volume. This finding is important for the rapidly evolving research field of photoresponsive thin films and smart crystalline materials in general. KW - Azobenzene PY - 2017 DO - https://doi.org/10.1088/1361-648X/aa8654 SN - 0953-8984 SN - 1361-648X VL - 29 IS - 43 SP - Article 434001, 1 EP - 8 AN - OPUS4-42501 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -