Ferroelasticity has been reported for several types of molecular crystals, which show mechanical‐stress‐induced shape change under twinning and/or spontaneous formation of strain. Aiming to create materials that exhibit both ferroelasticity and light‐emission characteristics, we discovered the first examples of ferroelastic luminescent organometallic crystals. Crystals of arylgold(I)(N‐heterocyclic carbene)(NHC) complexes bend upon exposure to anisotropic mechanical stress. X‐ray diffraction analyses and stress‐strain measurements on these ferroelastic crystals confirmed typical ferroelastic behavior, mechanical twinning, and the spontaneous build‐up of strain. A comparison with single‐crystal structures of related gold‐NHC complexes that do not show ferroelasticity shed light on the structural origins of the ferroelastic behavior.

The mechanism of plastic deformation in crystals of a trifluoromethylated benzamide derivative has been determined with micro-focused X-ray diffraction. Fuorine–fluorine interactions are propose to mediated the observed mechanical behaviour.

Chromism-color changes by external stimuli-has been intensively studied to develop smart materials because of easily detectability of the stimuli by eye or common spectroscopy as color changes. Luminescent chromism has particularly attracted research interest because of its high sensitivity. The color changes typically proceed in a one-way, two-state cycle, i.e. a stimulus-induced state will restore the initial state by another stimuli. Chromic systems showing instant, biphasic color switching and spontaneous reversibility will have wider practical applicability. Here we report luminescent chromism having such characteristics shown by mechanically controllable phase transitions in a luminescent organosuperelastic crystal. In mechanochromic luminescence, superelasticity-diffusion-less plastic deformation with spontaneous shape recoverability-enables real-time, reversible, and stepless control of the abundance ratio of biphasic color emissions via a single-crystal-to-single-crystal transformation by controlling a single stimulus, force stress. The unique chromic system, referred to as superelastochromism, holds potential for realizing informative molecule-based mechanical sensing.

Reaction of copper(II) benzoate with pyrazine (pyz) gave a compound, [Cu2(bz)4(pyz)]n (1) which has a gas-occlusion property. The X-ray structure analysis of 1·2nCH3CN shows a microporous structure formed by chains where the carboxylate dimer units are linked by pyrazine molecules.

Superelastic materials (crystal-to-crystal transformation pseudo elasticity) that consist of organic components have not been observed since superelasticity was discovered in a Au-Cd alloy in 1932. Superelastic materials have been exclusively developed in metallic or inorganic covalent solids, as represented by Ti-Ni alloys. Organosuperelasticity is now revealed in a pure organic crystal of terephthalamide, which precisely produces a large motion with high repetition and high energy storage efficiency. This process is driven by a small shear stress owing to the low density of strain energy related to the low lattice energy.A phase transition has been observed that is maintained in a single solid state induced by heat and pressure [1,2] and by light. [3] In that transition, the solid is affected by the structural distortion that occurs during transition. In an ideal case with the conservation of one-to-one correspondence of the atoms, the solid transformation is regarded as martensitic. [4] In the special case of martensitic transformation, the material acquires superelastic characteristics (transformation pseudo elasticity), which is important from a practical viewpoint and, in fact, is expected for the wide applications to structural materials and devices. Superelastic materials are primarily developed from metallic solids such as Ti-Ni alloys, and recently from ceramics. [5,6] Superelastic material made of organic components, which satisfies the definition of superelasticity, [7] has not been obvious over eight decades since superelasticity was first discovered in a Au-Cd alloy in 1932. [8] Based on the objective state of the current research trends related to superelastic materials, it might have been considered that covalent solids, which have a high degree of interatomic interaction, only fulfill the two essential requirements when being loaded with stress on the body: 1) Conservation of the one-to-one correspondence among neighboring atoms; and 2) storage of the elastic strain, which drives the spontaneous restoring motion back to the original state. In a comparison with the covalently interatomic interaction in alloys and ceramics, the relatively weak intermolecular interaction between organic components can be unreliable for generating superelasticity in molecular solids in which, furthermore, the molecular components vary in geometry and size. In investigating an organic superelastic system, we thought that the science of superelasticity could markedly advance by material diversification and functionalization, as chemical design can be effectively applied to superelastic materials. Thus, we were looking for a pure organic superelastic body as strict and simple as possible, and found the terephthalamide crystal as the first candidate for such a superelastic material. Its superelasticity was characterized by microscopy, stress tests, and X-ray diffraction analysis.Well-formed single crystals of terephthalamide (1) were obtained by recrystallization of a reagent-grade terephthalamide from hot water and used...