Dynamics in Flexible Pillar[<i>n</i>]arenes Probed by Solid-State NMR



Hughes, Ashlea R, Liu, Ming, Paul, Subhradip, Cooper, Andrew I and Blanc, Frederic
(2021) Dynamics in Flexible Pillar[<i>n</i>]arenes Probed by Solid-State NMR. JOURNAL OF PHYSICAL CHEMISTRY C, 125 (24). pp. 13370-13381.

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Abstract

Pillar[<i>n</i>]arenes are supramolecular assemblies that can perform a range of technologically important molecular separations which are enabled by their molecular flexibility. Here, we probe dynamical behavior by performing a range of variable-temperature solid-state NMR experiments on microcrystalline perethylated pillar[<i>n</i>]arene (<i>n</i> = 5, 6) and the corresponding three pillar[6]arene xylene adducts in the 100-350 K range. This was achieved either by measuring site-selective motional averaged <sup>13</sup>C <sup>1</sup>H heteronuclear dipolar couplings and subsequently accessing order parameters or by determining <sup>1</sup>H and <sup>13</sup>C spin-lattice relaxation times and extracting correlation times based on dipolar and/or chemical shift anisotropy relaxation mechanisms. We demonstrate fast motional regimes at room temperature and highlight a significant difference in dynamics between the core of the pillar[<i>n</i>]arenes, the protruding flexible ethoxy groups, and the adsorbed xylene guest. Additionally, unexpected and sizable <sup>13</sup>C <sup>1</sup>H heteronuclear dipolar couplings for a quaternary carbon were observed for <i>p</i>-xylene adsorbed in pillar[6]arene only, indicating a strong host-guest interaction and establishing the <i>p</i>-xylene location inside the host, confirming structural refinements.

Item Type: Article
Uncontrolled Keywords: 3403 Macromolecular and Materials Chemistry, 3405 Organic Chemistry, 34 Chemical Sciences
Divisions: Faculty of Science and Engineering > School of Physical Sciences
Depositing User: Symplectic Admin
Date Deposited: 16 Jun 2021 08:52
Last Modified: 20 Jun 2024 21:17
DOI: 10.1021/acs.jpcc.1c02046
Open Access URL: https://pubs.acs.org/doi/10.1021/acs.jpcc.1c02046
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URI: https://livrepository.liverpool.ac.uk/id/eprint/3126531