As altering permanent shapes without loss of material function is of practical importance for material molding, especially for elastic materials,s hape-rememorization ability would enhance the utility of elastic crystalline materials.Since diffusionless plastic deformability can preserve the crystallinity of materials,t he interconversion of diffusionless mechanical deformability between superelasticity and ferroelasticity could enable shape rememorization of superelastic single crystals.T his study demonstrates the shape rememorization of an organosuperelastic single crystal of 1,4-dicyanobenzene through time-reversible interconversion of superelasticity-ferroelasticity relaxation by holding the mechanically twinned crystal without heating. The shaperememorization ability of the organosuperelastic crystal indicates the compatibility of superelasticity (antiferroelasticity) and ferroelasticity as well as the intrinsic workability of organic crystalline materials capable of recovering their crystal functions under mild conditions. Practical applications of solid materials demand not only appropriate functions but also appropriate shapes.S ome polycrystalline and amorphous materials,s uch as alloys and polymers,are available in various shapes through molding in ad iffusion manner by thermal processes,i nw hich thermal stability is essential. On the other hand, reshaping singlecrystalline materials,i nw hich at hree-dimensional order is kept, is achieved by ac ombination of cutting,f iling, [1] and etching [2,3] according to their physical and chemical characteristics and intended use.R ecently,t he mechanical deformability of organic crystals has attracted great attention. Among their properties,s uperelasticity (SE) [18,[28][29][30][31] and ferroelasticity (FE) [19][20][21][22][23][24][25][26] give crystallographically well-regulated deformability while retaining single crystallinity. SE and FE have been developed in the fields of the materials science of metal alloys and the physics of ferroics, [32] respectively.M echanical deformations through both SE and FE are realized by diffusionless plastic deformability, whereby SE spontaneously recovers from strain and FE leaves permanent strain. In so-called shape-memory alloys (SMAs), [33][34][35] the shape is recovered because of the thermal generation of SE by as olid-state phase transition based on Gibbs free energy gaps,t hat is,m artensitic SE (mSE). Therefore,twinning deformation irrelevant to phase changes basically leads to twinning FE (tFE). Although tFE was claimed in an organic crystal of squaric acid in 1979, [19] tFE has now been identified in an increasing number of organic crystals and become commonplace in organic crystals composed of structurally flexible molecules. [19][20][21][22][23][24][25][26] Furthermore, multiple tFE effects with versatile deformability have been found in a1 ,4-diethoxybenzene crystal. [26] Tw inning deformability is apotential effective reshaping procedure for organic single crystals.Some organic crystals exhibit SE, so-called...

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.

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.

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Superelasticity is characterized by unique mechanical behavior, i.e., spontaneous shape recoverability by diffusionless plastic deformation and has been considered to be a property of specific alloys, so-called shape memory alloys, from its discovery in 1932. The discovery of superelasticity in an organic crystal in 2014, so-called organosuperelasticity, paved the way for functionalization of superelastic materials based on molecular design. In this context, achieving superelasiticity using various kinds of organic compounds and elucidation of its mechanism are inevitable. Here we show superelasticity in a single crystal of a derivative of sterically bulky cyclophanes: 4,5,7,8,12,13,15,16-octafluoro[2.2]paracyclophane. Crystallographic studies indicated interconversion of two centrosymmetric crystallographically independent molecules by changing molecular orientations in the crystalline state in twinning superelasticity. Our findings will contribute to propose one of the useful approaches for designing organosuperelastic materials.

Under the concept of supramolecular chemistry and crystal engineering, cocrystallization is one of the most widely used approaches for developing physical and other properties of crystals. Herein we report the first organoferroelastic cocrystal comprising oxalic acid and 4-chlorobenzamide showing a ferroelastic hysteresis loop, while single crystals of both of the components are non-ferroelastic.

The formation of two-component supramolecular polymers can lead to high supramolecular designability by a combination of different kinds of components in addition to the development of thermal and physical properties. These features are suitable for screening mechanical properties of low molecular crystals. Herein, we demonstrate ferroelasticity in a co-crystal of pimelic acid and 1,2-di­(4-pyridyl)­ethane, which form a one-dimensional supramolecular polymer by hydrogen bonds in the single crystalline state. The crystal showed a permanent biased ferroelastic hysteresis loop as a mixture of ferroelasticity and superelasticity, which is attributable to multiple crystallographically independent molecules.

Superelasticitydiffusion-less plastic deformation with spontaneous shape recoverabilityhas been applied to practical uses due to its unique mechanical characteristics, e.g., reversible deformability over elastic limit, and thermally induced shape recovery, the so-called shape-memory effect. For shaping shape-memory alloys showing superelasticity, they are aged under severe conditions unsuitable for organic materials, e.g., heating over several hundred degrees Celsius for several minutes to hours. Here we demonstrate shaping of a chiral organosuperelastic single crystal by quick shape-memorization processing at a temperature between 20 and 170 °C. Different from conventional shape-memory alloys, superelasticity of the crystal shows a small negative temperature dependence. Inversion of a polar direction and helical axis, induced by superelastic deformation in a crystal structure with a polar point group symmetry of 2, is also noteworthy from the viewpoint of polarity-based functions. The unveiled deformability will pave the way for development of organic crystalline materials, e.g., damping materials and structural materials, in soft robots.