Stress‐Induced Inversion of Linear Dichroism by 4,4′‐Bipyridine Rotation in a Superelastic Organic Single Crystal

Abstract

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.

Smart molecular crystal switches

“…Very recently, the group of Yao demonstrated stress-induced twinning of hydrogen-bonding cocrystal of 4,4 0 -bipyridinium 3,5-dimethylbenzoate. [42] By applying force along the diagonal corners of this crystal mechanoswitch, the crystal can be completely transformed between two twinning variants (Figure 7d). The net result is the switching of crystallographic a and b axes of the mother and daughter phases by rotating half of the pyridinyl groups by 90°.…”

“…(c) Interference color and birefringence change upon the phase transition of a ferrocene salt [76]. (d) Switching of light polarized direction by stress-induced twinning of single crystal of 4,4 0 -bipyridinium 3,5-dimethylbenzoate [42]. Reprint (adapted) with permission from Horie et al[76] and Li et al,[42] copyright 2007, 2023 John Wiley and Sons.…”

Metal–organic frameworks for the photocatalytic oxygen reduction reaction to hydrogen peroxide

“…67–73 MOFs, as a sort of hybrid materials, have the intersexuality associated with the rigidity of the inorganic crystal materials and the flexibility of the organic polymer materials. 74,75 Additionally, the coordination configurations between transition metals and organic linkers create the porosity of MOFs, while the uniform pores at the nanoscale can facilitate the adsorption of gas and liquid molecules such as CO 2 , O 2 , N 2 , CH 4 , C 3 H 6 , and benzene. 21,30,76–78…”

“…[67][68][69][70][71][72][73] MOFs, as a sort of hybrid materials, have the intersexuality associated with the rigidity of the inorganic crystal materials and the flexibility of the organic polymer materials. 74,75 Additionally, the coordination configurations between transition metals and organic linkers create the porosity of MOFs, while the uniform pores at the nanoscale can facilitate the adsorption of gas and liquid molecules such as CO 2 , O 2 , N 2 , CH 4 , C 3 H 6 , and benzene. 21,30,[76][77][78] Kitagawa and co-workers introduced chemical modulators into the solvothermal reaction to adjust the nucleation and the growth process of MOF nanocrystals via the competitive coordination between chemical modulators and ligands to optimize the geometry of MOFs.…”

Structural and Thermal Diffusivity Analysis of an Organoferroelastic Crystal Showing Scissor-Like Two-Directional Deformation Induced by Uniaxial Compression

“…The preconceived notion of such mechanical behaviors, which are typically limited to inorganic materials and polymers, is now shattered, and organic molecular crystals are considered an alternative structural material with the added benefits of low cost, easy processing, biocompatibility, and environmental friendliness . Various mechanical deformations in organic crystals, such as elastic, − plastic, − superelastic, − ferroelastic, − shape memory effect, , and various others − have been explored. Among these deformations, ferroelasticity exhibits ferroic properties in response to mechanical stress, similar to ferroelectricity and ferromagnetism.…”