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Abstract 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.
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Solid-state behaviors of imines: colossal biaxial positive thermal expansion, motion capability, and phase transitions
Pedal motion or static disorder in single-component solids containing imine groups is demonstrated. Unique solid-state behaviors including colossal biaxial positive thermal expansion in one solid and a temperature-dependent phase transition in another are discussed. Imines exhibit torsional flexibility, which differs from the isoelectronic azo and olefin groups and influences solid-state behaviors.
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- Award ID(s):
- 2045506
- PAR ID:
- 10316363
- Date Published:
- Journal Name:
- CrystEngComm
- Volume:
- 23
- Issue:
- 25
- ISSN:
- 1466-8033
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D1CE00706H
