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Colossal Anisotropic Thermal Expansion in a Diazo‐Functionalized Compound with Switchable Solid‐State Behavior

Achieving substantial anisotropic thermal expansion (TE) in solid‐state materials is challenging as most materials undergo volumetric expansion upon heating. Here, we describe colossal, anisotropic TE in crystals of an organic compound functionalized with two azo groups. Interestingly, the material...

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Bibliographic Details
Published in:Angewandte Chemie International Edition 2023-08, Vol.62 (33), p.e202306198-n/a
Main Authors: Ding, Xiaodan, Unruh, Daniel K., Ma, Liulei, Aalst, Evan J., Reinheimer, Eric W., Wylie, Benjamin J., Hutchins, Kristin M.
Format: Article
Language:English
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Summary:Achieving substantial anisotropic thermal expansion (TE) in solid‐state materials is challenging as most materials undergo volumetric expansion upon heating. Here, we describe colossal, anisotropic TE in crystals of an organic compound functionalized with two azo groups. Interestingly, the material exhibits distinct and switchable TE behaviors within different temperature regions. At high temperature, two‐dimensional, area zero TE and colossal, positive linear TE (α=211 MK−1) are attained due to dynamic motion, while at low temperature, moderate positive TE occurs in all directions. Investigation of the solid‐state motion showed the change in enthalpy and entropy are quite different in the two temperature regions and solid‐state NMR experiments support motion in the solid. Cycling experiments demonstrate that the solid‐state motions and TE behaviors are completely reversible. These results reveal strategies for designing significant anisotropic and switchable behaviors in solid‐state materials. The switchable solid‐state behavior of diazo‐I is described. Dramatically different and fully reversible thermal expansion (TE) behaviors are obtained on either side of a phase transition. Moderate, positive TE along all axes occurs at low temperature and two‐dimensional, area zero TE coupled with colossal, positive TE occurs at high temperature.
ISSN:1433-7851
1521-3773
DOI:10.1002/anie.202306198