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DOE OSTI · 1816426

Dynamics in Flexible Pillar[ n ]arenes Probed by Solid-State NMR

Hughes, Ashlea R.·Liu, Ming·Paul, Subhradip·Cooper, Andrew I.·Blanc, Frédéric
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Abstract

Pillar[n]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[n]arene (n = 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 13 C 1 H heteronuclear dipolar couplings and subsequently accessing order parameters or by determining 1 H and 13 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[n]arenes, the protruding flexible ethoxy groups, and the adsorbed xylene guest. Additionally, unexpected and sizable 13 C 1 H heteronuclear dipolar couplings for a quaternary carbon were observed for p-xylene adsorbed in pillar[6]arene only, indicating a strong host–guest interaction and establishing the p-xylene location inside the host, confirming structural refinements.

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRYcarboncoupling reactionsmagnetic propertiesmolecular propertiesnuclear magnetic resonance spectroscopy

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Hughes, Ashlea R., Liu, Ming, Paul, Subhradip, Cooper, Andrew I., Blanc, Frédéric. 2021-06-15. Dynamics in Flexible Pillar[ n ]arenes Probed by Solid-State NMR. https://doi.org/10.1021/acs.jpcc.1c02046

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