Cooperative light-induced breathing of soft porous crystals via azobenzene buckling

Although light is a prominent stimulus for smart materials, the application of photoswitches as light-responsive triggers for phase transitions of porous materials remains poorly explored. Here we incorporate an azobenzene photoswitch in the backbone of a metal-organic framework producing light-induced structural contraction of the porous network in parallel to gas adsorption. Light-stimulation enables non-invasive spatiotemporal control over the mechanical properties of the framework, which ultimately leads to pore contraction and subsequent guest release via negative gas adsorption. The complex mechanism of light-gated breathing is established by a series of in situ diffraction and spectroscopic experiments, supported by quantum mechanical and molecular dynamic simulations. Unexpectedly, this study identifies a novel light-induced deformation mechanism of constrained azobenzene photoswitches relevant to the future design of light-responsive materials

Massive Pressure Amplification by Stimulated Contraction of Mesoporous Frameworks

Negative Gas Adsorption (NGA), discovered in a series of mesoporous switchable MOFs, was hitherto regarded as a curios phenomenon occurring only at pressures well below or close to atmospheric merit. Herein we demonstrate mesoporous frameworks interacting with carbon dioxide, to show stimulated breathing transitions well above 100 kPa. Reversible CO2 adsorption-induced switching was observed in DUT-46 (DUT = Dresden University of Technology), in contrast to irreversible transitions for DUT-49 and DUT-50, as demonstrated via synchrotron in situ PXRD/adsorption experiments. Systematic physisorption experiments reveal the best conditions for high pressure NGA transitions in the pressure range of 350 - 680 kPa. The stimulated framework contraction expells CO2 in the range of 1.1 to 2.4 mmol g-1 leading to autonomous pressure amplification in a closed system. In a pneumatic demonstrator system we achieved pressure amplification of 90 kPa at a high operating pressure of 340 kPa. According to system level estimations even higher theoretical pressure amplification may be achieved between 535 kPa and 1011 kPa for DUT-49 using CO2 as a non-toxic and non-flammable working gas. Operable pressure ranges exceeding 100 kPa render pressure amplifying framework materials as realistic candidates for the integration into energy autonomous responsive pneumatic systems

The Role of Temperature and Adsorbate on Negative Gas Adsorption in the Mesoporous Metal-Organic Framework DUT-49

In this contribution, we present an extensive investigation of adsorption of a range of different gases at various temperatures in DUT-49, a metal-organic framework which features a negative gas adsorption (NGA) transition. Adsorption experiments at temperatures ranging from 21 to 308 K, were used to identify, for each guest, a critical temperature range in which NGA occurs. The experimental results were complemented by molecular simulations that rationalize the absence of NGA at elevated temperatures and the non-monotonic behavior observed upon temperature decrease

Cooperative Light-Induced Breathing of Soft Porous Crystals via Azobenzene Buckling

Although light is a prominent stimulus for smart materials, the application of photoswitches as light-responsive triggers for phase transitions of porous materials remains poorly explored. Here we incorporate an azobenzene photoswitch in the backbone of a metal-organic framework producing light-induced structural contraction of the porous network in parallel to gas adsorption. Light-stimulation enables non-invasive spatiotemporal control over the mechanical properties of the framework, which ultimately leads to pore contraction and subsequent guest release via negative gas adsorption. The complex mechanism of light-gated breathing is established by a series of in situ diffraction and spectroscopic experiments, supported by quantum mechanical and molecular dynamic simulations. Unexpectedly, this study identifies a novel light-induced deformation mechanism of constrained azobenzene photoswitches relevant to the future design of light-responsive materials

Engineering Micromechanics of Soft Porous Crystals for Negative Gas Adsorption

Framework materials at the molecular level, such as metal-organic frameworks (MOF), were recently found to exhibit exotic and counterintuitive micromechanical properties. Stimulated by host-guest interactions, these so-called soft porous crystals can display counterintuitive adsorption phenomena such as negative gas adsorption (NGA). NGA materials are bistable frameworks where the occurrence of a metastable overloaded state leads to pressure amplification upon a sudden framework contraction. How can we control activation barriers and energetics via functionalization of the molecular building blocks that dictate the frameworks’ 30 mechanical response? In this work we tune the elastic and inelastic properties of building blocks at the 31 molecular level and analyze the mechanical response of the resulting frameworks. From a set of 11 frameworks, we demonstrate that widening of the backbone increases elasticity, while elongation of the building blocks results in a decrease in critical yield stress of buckling. We further functionalize the backbone by incorporation of sp3 hybridized carbon atoms to soften the molecular building blocks, or stiffen them with sp2 and sp carbons. Computational modeling shows how these modifications of the building blocks tune the 36 activation barriers within the energy landscape of the guest-free bistable frameworks. Only frameworks with free energy barriers in the range of 800 to 1100 kJ mol–1 37 per unit cell, and moderate yield stress of 0.6 to 38 1.2 nN for single ligand buckling, exhibit adsorption-induced contraction and negative gas adsorption. Advanced experimental in situ methodologies give detailed insights into the structural transitions and the adsorption behavior. The new framework DUT-160 shows the highest magnitude of NGA ever observed for nitrogen adsorption at 77 K. Our computational and experimental analysis of the energetics and mechanical response functions of porous frameworks is an important step towards tuning activation barriers in dynamic framework materials and provides critical design principles for molecular building blocks leading to pressure amplifying materials<br /

Towards General Network Architecture Design Criteria for Negative Gas Adsorption Transitions in Ultraporous Frameworks

Critical design criteria for negative gas adsorption (NGA), a counterintuitive feature of pressure amplifying materials, hitherto uniquely observed in a highly porous framework compound (DUT-49), are derived by analysing the physical effects of micromechanics, pore size, interpenetration, adsorption enthalpies, and the pore filling mechanism using advanced in situ X-ray and neutron diffraction, NMR spectroscopy, and calorimetric techniques parallelized to adsorption for a series of six isoreticular networks. Aided by computational modelling, we identify DUT-50 as a new pressure amplifying material featuring distinct NGA transitions upon methane and argon adsorption. In situ neutron diffraction analysis of the methane (CD4) adsorption sites at 111 K supported by grand canonical Monte Carlo simulations reveals a sudden population of the largest mesopore to be the critical filling step initiating structural contraction and NGA. In contrast, interpenetration leads to framework stiffening and specific pore volume reduction, both factors effectively suppressing NGA transitions.</p

CCDC 2003154: Experimental Crystal Structure Determination

Related Article: Simon Krause, Jack D. Evans, Volodymyr Bon, Irena Senkovska, Sebastian Ehrling, Paul Iacomi, Daniel D. Többens, Dirk Wallacher, Manfred S. Weiss, Bin Zheng, Pascal G. Yot, Guillaume Maurin, Philip L. Llewellyn, François-Xavier Coudert, Stefan Kaskel|2020|ChemRxiv|||doi:10.26434/chemrxiv.12619064,Related Article: Simon Krause, Jack D. Evans, Volodymyr Bon, Irena Senkovska, Sebastian Ehrling, Paul Iacomi, Daniel M. Többens, Dirk Wallacher, Manfred S. Weiss, Bin Zheng, Pascal G. Yot, Guillaume Maurin, Philip L. Llewellyn, François-Xavier Coudert, Stefan Kaskel|2020|Chemical Science|11|9468|doi:10.1039/D0SC03727C

CCDC 2003153: Experimental Crystal Structure Determination

Related Article: Simon Krause, Jack D. Evans, Volodymyr Bon, Irena Senkovska, Sebastian Ehrling, Paul Iacomi, Daniel D. Többens, Dirk Wallacher, Manfred S. Weiss, Bin Zheng, Pascal G. Yot, Guillaume Maurin, Philip L. Llewellyn, François-Xavier Coudert, Stefan Kaskel|2020|ChemRxiv|||doi:10.26434/chemrxiv.12619064,Related Article: Simon Krause, Jack D. Evans, Volodymyr Bon, Irena Senkovska, Sebastian Ehrling, Paul Iacomi, Daniel M. Többens, Dirk Wallacher, Manfred S. Weiss, Bin Zheng, Pascal G. Yot, Guillaume Maurin, Philip L. Llewellyn, François-Xavier Coudert, Stefan Kaskel|2020|Chemical Science|11|9468|doi:10.1039/D0SC03727C

CCDC 2003152: Experimental Crystal Structure Determination

Related Article: Simon Krause, Jack D. Evans, Volodymyr Bon, Irena Senkovska, Sebastian Ehrling, Paul Iacomi, Daniel D. Többens, Dirk Wallacher, Manfred S. Weiss, Bin Zheng, Pascal G. Yot, Guillaume Maurin, Philip L. Llewellyn, François-Xavier Coudert, Stefan Kaskel|2020|ChemRxiv|||doi:10.26434/chemrxiv.12619064,Related Article: Simon Krause, Jack D. Evans, Volodymyr Bon, Irena Senkovska, Sebastian Ehrling, Paul Iacomi, Daniel M. Többens, Dirk Wallacher, Manfred S. Weiss, Bin Zheng, Pascal G. Yot, Guillaume Maurin, Philip L. Llewellyn, François-Xavier Coudert, Stefan Kaskel|2020|Chemical Science|11|9468|doi:10.1039/D0SC03727C

CCDC 2003150: Experimental Crystal Structure Determination

Related Article: Simon Krause, Jack D. Evans, Volodymyr Bon, Irena Senkovska, Sebastian Ehrling, Paul Iacomi, Daniel D. Többens, Dirk Wallacher, Manfred S. Weiss, Bin Zheng, Pascal G. Yot, Guillaume Maurin, Philip L. Llewellyn, François-Xavier Coudert, Stefan Kaskel|2020|ChemRxiv|||doi:10.26434/chemrxiv.12619064,Related Article: Simon Krause, Jack D. Evans, Volodymyr Bon, Irena Senkovska, Sebastian Ehrling, Paul Iacomi, Daniel M. Többens, Dirk Wallacher, Manfred S. Weiss, Bin Zheng, Pascal G. Yot, Guillaume Maurin, Philip L. Llewellyn, François-Xavier Coudert, Stefan Kaskel|2020|Chemical Science|11|9468|doi:10.1039/D0SC03727C