科研之友
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摘要
The molecular crystals that manifest unusual mechanical properties have attracted growing attention. Herein, we prepared an organic single crystal that shows bidirectional superelastic transformation in response to shear stress. Single‐crystal X‐ray diffractions revealed this crystal‐twinning related shape change is owed to a stress‐controlled 90° rotation of 4,4′‐bipyridine around the hydrogen bonds of a chiral organic trimer. As a consequence of the 90° shift in the aromatic plane, an interconversion of crystallographic a‐, b‐axes (a→b′ and b→a′) was detected. The molecular rotations changed the anisotropic absorption of linearly polarized light. Therefore, a stress‐induced inversion of linear dichroism spectra was demonstrated for the first time. This study reveals the superior mechanical flexibilities of single crystals can be realized by harnessing the molecular rotations and this superelastic crystal may find applications in optical switching and communications.(#br)A 4,4′‐bipyridine molecule in a hydrogen‐bonded molecular trimer can be rotated 90° around the hydrogen bonds, leading to a single‐crystal superelastic deformation associated with a reversible inversion of linear dichroism spectra.
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