Satoshi Takamizawa

The precise, reversible, and diffusionless shape-switching ability of organic ferroelastic crystals, while maintaining their structural integrity, positions them as promising materials for next-generation hybrid photonic devices. Herein, we present versatile bi-directional ferroelasticity and optical waveguide properties of three isomorphous, halogen-based, Schiff base organic crystals. These crystals exhibit sharp bending at multiple interfaces driven by molecular movement around the CH = N bond and subsequent 180° rotational twinning, offering controlled light path manipulation. The ferroelastic nature of these crystals allowed the construction of robust hybrid photonic structures, including Z-shaped configurations, closed-loop networks, and staircase-like hybrid optical waveguides. This study highlights the potential of shape-switchable organoferroelastic crystals as waveguides for applications in programmable photonic devices.

Crystalline materials that exhibit reversible mechanical responses upon exposure to external stimuli have garnered significant attention owing to their potential applications in various fields. Herein, we report a crystal of (2Z,2′Z)-2,2′-(1,4-phenylene)bis(3-(4-bromophenyl)acrylonitrile) (DSBr), which displays simultaneous elasto-plastic behaviour and reversible thermosalient effects. While elasto-plastic behaviour is attributed to underlying packing features, reversible thermosalient expansion is attributed to uniaxial expansion mediated by heat. Exceptional length increase and contraction upon cooling is due to the restorative nature of weak interactions through a cooperative effect. The cooperative movement of molecules is reflected in the unidirectional expansion of the habit plane. Thermosalient reversible expansion–contraction in elasto-plastic crystals have not been discussed in the literature so far. Detailed analysis reported herein provides a comprehensive understanding of the underlying mechanism of flexibility and thermosalient responses. This crystal's unique blend of reversible thermal expansion with flexibility holds substantial promise for applications in flexible thermal actuators.

We report an unprecedented result of self‐aggregation of [Pt(L¹)Cl] (HL¹=1,3‐di(5‐carboxy‐2‐pyridyl)benzene) triggered by CO₂ in basic aqueous solution. The color of basic aqueous solution containing [Pt(L¹)Cl] changes from yellow to blue‐green during the aggregation resulted from a reaction with CO₂ in air. Upon CO₂ gas bubbling, strong and broad absorption bands of aggregate assigned to the metal‐metal‐to‐ligand charge‐transfer transition appeared at 701 and 1152 nm. Recrystallization of [Pt(L¹)Cl] from Na₂CO₃ aqueous solution afforded polymorphic crystals of red and blue‐green forms. A single X‐ray crystallography revealed that the red form of crystal consists of a Pt−Pt stacked dimer bridged by CO₃²⁻ ion and one of the carboxy groups of L¹ is deprotonated. An elemental analysis provided evidence that the blue‐green crystal is constructed by linear array consisting of the [Pt(L²)(CO₃)]³⁻ (HL²=1,3‐di(5‐carboxylate‐2‐pyridyl)benzene) units. The formation process of blue‐green aggregate in aqueous solution was monitored through a transient absorption spectrum, and the absorption of aggregates involved in the spectral change were examined by a global analysis. A singular value decomposition and kinetic analysis provide that there are four species resulted from the self‐assembling reaction in the solution and the maximal degree of aggregation is at least 32‐mer.

Anisotropic thermal diffusivity correlates with the intermolecular interactions in two cocrystals with varying halogen acceptor abilities, which also influenced the superelastic and ferroelastic behaviour.

A two-directional ferroelastic deformation in organic crystals is unprecedented owing to its anisotropic crystal packing, in contrast to isotropic symmetrical packing in inorganic compounds and polymers. Thereby, finding and constructing multidirectional ferroelastic deformations in organic compounds is undoubtedly complex and at once calls for deep comprehension. Herein, we demonstrate the first example of a two-directional ferroelastic deformation with a unique scissor-like movement in single crystals of trans-3-hexenedioic acid by the application of uniaxial compression stress. A detailed structural investigation of the mechanical deformation at the macroscopic and microscopic levels by three distinct force measurement techniques (including shear and three-point bending test), single crystal X-ray diffraction techniques, and polarized synchrotron-FTIR microspectroscopy highlighted that mechanical twinning promoted the deformation. The presence of two crystallographically equivalent faces and the herringbone arrangement promoted the two-directional ferroelastic deformation. In addition, anisotropic heat transfer properties in the parent and the deformed domains were investigated by thermal diffusivity measurement on all three axes using microscale temperature-wave analysis (μ-TWA). A correlation between the anisotropic structural arrangement and the difference in thermal diffusivity and mechanical behavior in the two-directional organoferroelastic deformation could be established. The structural and molecular level information from this two-directional ferroelastic deformation would lead to a more profound understanding of the structure-property relationship in multidirectional deformation in organic crystals.

This study provides the first evidence that a Li ion can form ionic plastic crystals using crown ether with a bis-(trifluoromethanesulphonyl) amide (TFSA) anion. ¹H, ⁷Li, and ¹³C nuclear-magnetic-resonance (NMR) measurements of the 15-crown-5–Li-TFSA complex revealed that the constituents underwent isotropic reorientation in the plastic crystalline phase. The NMR data of the 12-crown-4–Li-TFSA salt showed that the complex is a rotator crystal (the complexes are denoted as [Li 15C5] and [Li 12C4] in this paper). The X-ray diffraction (XRD) reflection patterns of the [Li 15C5] crystal recorded in the highest-temperature solid phase (plastic phase) could be indexed to a cubic structure. Conversely, [Li 12C4] could be fitted to a trigonal structure. In this study, [M (3n)Cn] (M = Li, Na, K; n = 4–6) complexes were also prepared, and NMR, DSC, XRD, and electrical conductivity measurements were performed. Based on these results, we additionally revealed that the [Na 15C5] and [K (15C5)₂] complexes are also new rotator crystals. Single-crystal XRD measurements also revealed that the [Na 15C5] compound has two stable sites in the crystal. Activation energies of molecular motions in the [M (3n)Cn] crystals were estimated using ¹H NMR relaxation time (T₁ and T₂) measurements. The electrical conductivity measurements of [Li 12C4], [Li 15C5], and [Na 15C5] showed high ionic conductivities (∼10⁻² S cm⁻¹).

Superelasticity is the ability of a plastically deformed solid to spontaneously recover its shape upon unloading due to stress loading. From its discovery in Au–Cd alloys in 1932, superelasticity had been believed to be limited to certain alloys until the discovery of “organic superelasticity” in 2014, which revealed it to be a general phenomenon observed in organic crystals along with ferroelasticity—reversible plastic deformability that is not accompanied by spontaneous shape recovery. In this chapter, we will introduce the discovery of organic superelasticity and the shape-memory effect, discuss superelasticity and ferroelasticity, and explain the properties and characteristics of various molecular crystals, including metal complexes. Furthermore, “organic superplasticity”—irreversible plastic deformation of several hundred percent or more, accompanied by the retention of crystallinity—has also been described.

Molecular crystals of Pt(II) complexes with metallophilic interactions can provide bright assembly-induced luminescence with colour tunability. However, the brittleness of many of these crystals makes their application in flexible optical materials difficult. Herein, we have achieved the elastic deformation of crystals of polyhalogenated Pt(II) complexes exhibiting bright assembly-induced luminescence. A crystal of [Pt(bpic)(dFppy)] (Hbpic = 5-bromopicolinic acid, HdFppy = 2-(2,4-difluorophenyl)pyridine) and a co-crystal of [Pt(bpic)(dFppy)] and [Pt(bpic)(ppy)] (Hppy = 2-phenylpyridine) were found to exhibit significant elastic deformation due to their highly anisotropic interaction topologies. While the crystal of [Pt(bpic)(dFppy)] exhibited monomer-based ligand-centred ³ππ* emission with an emission quantum yield of 0.40, the co-crystal exhibited bright, triplet metal–metal-to-ligand charge transfer (³MMLCT) emission owing to Pt⋯Pt interactions, thereby achieving a significantly higher emission quantum yield of 0.94.

Herein, we report our results on the synthetic studies of the originally proposed structure of protoaculeine B, isolated from a marine sponge. Starting from tryptophan, two candidates of the suitably protected heterotricyclic subunits were stereoselectively synthesized over 8 and 16 steps, respectively. Furthermore, two diastereomeric heterotricyclic amino acids, finally synthesized, were found to be neuroactive: the (9S*,11S*)‐isomer with natural‐type configuration was hyperactive, whereas diastereomeric (9S*,11R*)‐isomer was hypoactive upon mice intracerebroventricular injection.