Molecular Rotors, especially when bearing dipoles, are an attractive research field entailing a number of useful phenomena, such as switchable ferroelectricity, and the fabrication of dynamic elements of molecular motors in solids. In turn, Porous Materials are an innovative playground for supporting switchable molecular rotors. We have recently discovered hybrid porous materials with intrinsic dynamics due to the presence of fast molecular rotors in their architectures (correlation times in the nanoseconds) [1,2]. Indeed, the precise engineering of highly-organized porous silica scaffolds supporting organic elements allowed the fabrication of fast (k>108 Hz) molecular rotors, such as p-phenylene units and dipolar rotors containing C-F dipoles. Such dipolar rotors face the pores and are entirely exposed to the guest molecules which acted as regulators. Powder X-ray diffraction and solid state NMR helped to disclose the relaxation and motional trajectories of chemical groups in the frameworks. In the case of dipolar molecular rotors also a dielectric response typical of a fast dipole reorientation under the stimuli of an applied electric field was detected. We achieved the systematic regulation of the rotor speed by the intervention of chemical species diffusing in such as I2, opening unconventional perspectives in responsive materials. The combination of porosity with rotor dynamics was also disclosed in porous organic frameworks PAFs [3]. The constructive elements contain rapid rotors, resulting in a dynamic material whose motion can be frozen or released at will. The rotational motion was actively regulated in response to guests such as n-alkanes and iodine. Thanks to the robustness of these materials it was possible to study the rotor dynamics at extremely high temperatures: as the temperature is increased, the rotors spin even faster, approaching free-rotational diffusion at 550 K. The remarkable porosity with fast dynamics is intriguing for engineering oscillating dipoles and producing responsive materials, for applications spanning from sensors to actuators, which capture and release chemicals on command. A first example of molecular rotors in porous molecular crystals is presented. Disulfonated rotor-containing molecular rods were self-assembled with alkylammonium salts to fabricate porous supramolecular architectures held together by charge-assisted hydrogen bonds[4]. The rotors, as fast as 108 Hz at 240 K, are exposed to the crystalline channels, which absorb CO2 and I2 vapors at low pressure. The rotor dynamics could be switched off and on by I2 absorption/desorption, showing remarkable change of material dynamics by the interaction with gaseous species and suggesting the use of molecular crystals in sensing and pollutant management. Moreover, the surfaces of inclusion crystals were decorated with regular arrays of dipolar molecular rotors by the insertion of dipolar rotators carrying alkyl chains which are included as guests into channels of a host, tris(o-phenylenedioxy)cyclotriphosphazene (TPP) [5]. The rotors stay at the surface due to a bulky molecular stopper which prevents the rotors from entering the channels while the alkyl chains are included in the crystals. The host-guest relationships were established by 2D solid-state NMR and low rotational barriers were found by dielectric spectroscopy. [1] S. Bracco, A. Comotti, M. Beretta, A. Cattaneo, A. Falqui, K. Zhao, C. Rogers, P. Sozzani Angew. Chemie Int. Ed. 2015, ASAP (VIP Article). [2] A. Comotti, S. Bracco, P. Valsesia, M. Beretta, P. Sozzani Angew. Chem. Int. Ed. 2010, 49, 1760. [3] Angiolina Comotti, Silvia Bracco, Teng Ben, Shilun Qiu, and Piero Sozzani Angew. Chem. Int. Ed. 2014, 53, 1043 –1047. [4] A. Comotti, S. Bracco, A. Yamamoto, M. Beretta, T. Hirukawa, N. Tohnai, M. Miyata, P. Sozzani J. Am. Chem. Soc. 2014, 136, 618. [5] L. Kobr, K. Zhao, Y. Shen, A. Comotti, S. Bracco, R. K. Shoemaker, P. Sozzani, N. A. Clark, J. C. Price, C. T. Rogers, J. Michl J. Am. Chem. Soc. 2012, 134, 10122.
Comotti, A. (2015). Porosity and Molecular Rotor Dynamics in Covalent Frameworks and Supramolecular Architectures [Altro].
Porosity and Molecular Rotor Dynamics in Covalent Frameworks and Supramolecular Architectures
COMOTTI, ANGIOLINA
2015
Abstract
Molecular Rotors, especially when bearing dipoles, are an attractive research field entailing a number of useful phenomena, such as switchable ferroelectricity, and the fabrication of dynamic elements of molecular motors in solids. In turn, Porous Materials are an innovative playground for supporting switchable molecular rotors. We have recently discovered hybrid porous materials with intrinsic dynamics due to the presence of fast molecular rotors in their architectures (correlation times in the nanoseconds) [1,2]. Indeed, the precise engineering of highly-organized porous silica scaffolds supporting organic elements allowed the fabrication of fast (k>108 Hz) molecular rotors, such as p-phenylene units and dipolar rotors containing C-F dipoles. Such dipolar rotors face the pores and are entirely exposed to the guest molecules which acted as regulators. Powder X-ray diffraction and solid state NMR helped to disclose the relaxation and motional trajectories of chemical groups in the frameworks. In the case of dipolar molecular rotors also a dielectric response typical of a fast dipole reorientation under the stimuli of an applied electric field was detected. We achieved the systematic regulation of the rotor speed by the intervention of chemical species diffusing in such as I2, opening unconventional perspectives in responsive materials. The combination of porosity with rotor dynamics was also disclosed in porous organic frameworks PAFs [3]. The constructive elements contain rapid rotors, resulting in a dynamic material whose motion can be frozen or released at will. The rotational motion was actively regulated in response to guests such as n-alkanes and iodine. Thanks to the robustness of these materials it was possible to study the rotor dynamics at extremely high temperatures: as the temperature is increased, the rotors spin even faster, approaching free-rotational diffusion at 550 K. The remarkable porosity with fast dynamics is intriguing for engineering oscillating dipoles and producing responsive materials, for applications spanning from sensors to actuators, which capture and release chemicals on command. A first example of molecular rotors in porous molecular crystals is presented. Disulfonated rotor-containing molecular rods were self-assembled with alkylammonium salts to fabricate porous supramolecular architectures held together by charge-assisted hydrogen bonds[4]. The rotors, as fast as 108 Hz at 240 K, are exposed to the crystalline channels, which absorb CO2 and I2 vapors at low pressure. The rotor dynamics could be switched off and on by I2 absorption/desorption, showing remarkable change of material dynamics by the interaction with gaseous species and suggesting the use of molecular crystals in sensing and pollutant management. Moreover, the surfaces of inclusion crystals were decorated with regular arrays of dipolar molecular rotors by the insertion of dipolar rotators carrying alkyl chains which are included as guests into channels of a host, tris(o-phenylenedioxy)cyclotriphosphazene (TPP) [5]. The rotors stay at the surface due to a bulky molecular stopper which prevents the rotors from entering the channels while the alkyl chains are included in the crystals. The host-guest relationships were established by 2D solid-state NMR and low rotational barriers were found by dielectric spectroscopy. [1] S. Bracco, A. Comotti, M. Beretta, A. Cattaneo, A. Falqui, K. Zhao, C. Rogers, P. Sozzani Angew. Chemie Int. Ed. 2015, ASAP (VIP Article). [2] A. Comotti, S. Bracco, P. Valsesia, M. Beretta, P. Sozzani Angew. Chem. Int. Ed. 2010, 49, 1760. [3] Angiolina Comotti, Silvia Bracco, Teng Ben, Shilun Qiu, and Piero Sozzani Angew. Chem. Int. Ed. 2014, 53, 1043 –1047. [4] A. Comotti, S. Bracco, A. Yamamoto, M. Beretta, T. Hirukawa, N. Tohnai, M. Miyata, P. Sozzani J. Am. Chem. Soc. 2014, 136, 618. [5] L. Kobr, K. Zhao, Y. Shen, A. Comotti, S. Bracco, R. K. Shoemaker, P. Sozzani, N. A. Clark, J. C. Price, C. T. Rogers, J. Michl J. Am. Chem. Soc. 2012, 134, 10122.
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