The enormous interest manifested in recent years for porous materials has generated efficient systems for adsorbing gases of great interest for energy and the environment, such as CO2, CH4 and H2. Our approach was to design porosity in combination with switchable dynamics and flexibility for gaining control over gas capture and selectivity. This approach was made possible by fabricating rotor-on-axel molecular struts and tetrahedral building blocks. Rotor-on-axel molecular struts. Ultra-fast molecular rotors were realized in porous solids by engineering crystalline frameworks (molecular crystals, MOFs and mesoporous organosilicas) containing rod-like linkers as amphidynamic elements.1-5 The porous frameworks promise access to the control of rotary motion by chemical and physical stimuli. We prepared rotors as fast as 1011 Hz (in the regime of conventional liquids) in properly designed porous crystals. Rotor dynamics was successfully hampered by the diffusion of gases or vapors. In turn, the on/off switching of dynamics produces modulated physical responses when C-F dipoles were mounted on the rotors.6 Direct evidence of host-guest relationships and interactions at the molecular level were established by 2D solid-state NMR and modelled by ab initio calculations. Tetrahedral building-blocks. In the search for flexible molecular crystals endowed with porosity, we achieved the fabrication of expandable crystalline prototypal structures, which allow for the absorption of gases, without modifying the crystal architecture.7 The design brings together highly symmetrical tetrahedral elements to construct swellable porous adamantoid frameworks. The flexibility of the porous crystals manifests itself in response to stimuli of selected gases: the contact with CO2, Xe and hexane triggers the enlargement of channel cross-section and capacity. The accomodation of CO2 and Xe in the channel chambers was revealed by synchrotron-light XRD, combined with Molecular Dynamics and DFT calculations. Xenon dynamics, exploring various cavity orientations in the crystal, were gathered by 129Xe NMR chemical shift anisotropy profiles, which encode the shape and orientation of each visited cavity. Jump rate and activation energy experienced by exploring Xe atoms were uniquely established. Moreover, photo-responsive molecular crystals were fabricated by a series of tetrahedral azobenzene tetramers that form porous molecular crystals in their trans configuration.8 The efficient trans-to-cis photoisomerization of the azobenzene units converts the crystals into a non-porous phase but crystallinity and porosity are restored upon cis-to-trans reverse isomerization promoted by visible light or heat. We demonstrated that the photo-isomerization enables reversible on/off switching of optical properties as well as CO2 capture from the gas phase. Acknowldegements to PRIN 2016 2016-NAZ-0104 (1) A. Comotti, A. et al. Acc. Chem. Res. 49 (2016) 1701-1710. (2) S. Bracco, et al. Chem. Eur. J. 23 (2017) 11210. (3) A. Comotti, et al. J. Am. Chem. Soc. 136 (2014) 618. (4) A. Comotti, et al. Angew. Chem. Int. Ed. 53 (2014) 1043. (5) S. Bracco, et al. Chem. Comm. 53 (2017) 7776. (6) S. Bracco, et al. Angew. Chem. Int Ed. 54 (2015) 4773. (7) I. Bassanetti, et al. J. Mater. Chem. A 6 (2018) 14231. (8) M. Baroncini, et al. Nature Chem. 7 (2015) 634.

Comotti, A., Bracco, S., Castiglioni, F., Pedrini, A., Sozzani, P. (2018). Dynamics and Flexibility in Gas-absorptive Porous Materials. In Book of Abstracts.

Dynamics and Flexibility in Gas-absorptive Porous Materials

Comotti, A;Bracco, S
Membro del Collaboration Group
;
Castiglioni, F
Membro del Collaboration Group
;
Pedrini, A;Sozzani, P
Membro del Collaboration Group
2018

Abstract

The enormous interest manifested in recent years for porous materials has generated efficient systems for adsorbing gases of great interest for energy and the environment, such as CO2, CH4 and H2. Our approach was to design porosity in combination with switchable dynamics and flexibility for gaining control over gas capture and selectivity. This approach was made possible by fabricating rotor-on-axel molecular struts and tetrahedral building blocks. Rotor-on-axel molecular struts. Ultra-fast molecular rotors were realized in porous solids by engineering crystalline frameworks (molecular crystals, MOFs and mesoporous organosilicas) containing rod-like linkers as amphidynamic elements.1-5 The porous frameworks promise access to the control of rotary motion by chemical and physical stimuli. We prepared rotors as fast as 1011 Hz (in the regime of conventional liquids) in properly designed porous crystals. Rotor dynamics was successfully hampered by the diffusion of gases or vapors. In turn, the on/off switching of dynamics produces modulated physical responses when C-F dipoles were mounted on the rotors.6 Direct evidence of host-guest relationships and interactions at the molecular level were established by 2D solid-state NMR and modelled by ab initio calculations. Tetrahedral building-blocks. In the search for flexible molecular crystals endowed with porosity, we achieved the fabrication of expandable crystalline prototypal structures, which allow for the absorption of gases, without modifying the crystal architecture.7 The design brings together highly symmetrical tetrahedral elements to construct swellable porous adamantoid frameworks. The flexibility of the porous crystals manifests itself in response to stimuli of selected gases: the contact with CO2, Xe and hexane triggers the enlargement of channel cross-section and capacity. The accomodation of CO2 and Xe in the channel chambers was revealed by synchrotron-light XRD, combined with Molecular Dynamics and DFT calculations. Xenon dynamics, exploring various cavity orientations in the crystal, were gathered by 129Xe NMR chemical shift anisotropy profiles, which encode the shape and orientation of each visited cavity. Jump rate and activation energy experienced by exploring Xe atoms were uniquely established. Moreover, photo-responsive molecular crystals were fabricated by a series of tetrahedral azobenzene tetramers that form porous molecular crystals in their trans configuration.8 The efficient trans-to-cis photoisomerization of the azobenzene units converts the crystals into a non-porous phase but crystallinity and porosity are restored upon cis-to-trans reverse isomerization promoted by visible light or heat. We demonstrated that the photo-isomerization enables reversible on/off switching of optical properties as well as CO2 capture from the gas phase. Acknowldegements to PRIN 2016 2016-NAZ-0104 (1) A. Comotti, A. et al. Acc. Chem. Res. 49 (2016) 1701-1710. (2) S. Bracco, et al. Chem. Eur. J. 23 (2017) 11210. (3) A. Comotti, et al. J. Am. Chem. Soc. 136 (2014) 618. (4) A. Comotti, et al. Angew. Chem. Int. Ed. 53 (2014) 1043. (5) S. Bracco, et al. Chem. Comm. 53 (2017) 7776. (6) S. Bracco, et al. Angew. Chem. Int Ed. 54 (2015) 4773. (7) I. Bassanetti, et al. J. Mater. Chem. A 6 (2018) 14231. (8) M. Baroncini, et al. Nature Chem. 7 (2015) 634.
paper
porosity, gas adsorption, CO2, CH4, solid state NMR, molecular rotors, 129Xe NMR
English
ISMS III - International Symposium for Materials Scientists III (Osaka, Japan, 3-4 dicembre 2018)
2018
Book of Abstracts
2018
none
Comotti, A., Bracco, S., Castiglioni, F., Pedrini, A., Sozzani, P. (2018). Dynamics and Flexibility in Gas-absorptive Porous Materials. In Book of Abstracts.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/219169
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