Flexible ferroelectric organic crystals

Exceptionally Plastic/Elastic Organic Crystals of a Naphthalidenimine-Boron Complex Show Flexible Optical Waveguide Properties

The design of molecular compounds that exhibit flexibility is an emerging area of research. Although a fair amount of success has been achieved in the design of plastic or elastic crystals, realizing multidimensional plastic and elastic bending remains challenging. We report herein a naphthalidenimine-boron complex that showed size-dependent dual mechanical bending behavior whereas its parent Schiff base was brittle. Detailed crystallographic and spectroscopic analysis revealed the importance of boron in imparting the interesting mechanical properties. Furthermore, the luminescence of the molecule was turned-on subsequent to boron complexation, thereby allowing it to be explored for multimode optical waveguide applications. Our in-depth study of the size-dependent plastic and elastic bending of the crystals thus provides important insights in molecular engineering and could act as a platform for the development of future smart flexible materials for optoelectronic applications.

Recent Progress in the Nanoscale Evaluation of Piezoelectric and Ferroelectric Properties via Scanning Probe Microscopy

Piezoelectric and ferroelectric materials have garnered significant interest owing to their excellent physical properties and multiple potential applications. Accordingly, the need for evaluating piezoelectric and ferroelectric properties has also increased. The piezoelectric and ferroelectric properties are evaluated macroscopically using laser interferometers and polarization-electric field loop measurements. However, as the research focus is shifted from bulk to nanosized materials, scanning probe microscopy (SPM) techniques have been suggested as an alternative approach for evaluating piezoelectric and ferroelectric properties. In this Progress Report, the recent progress on the nanoscale evaluation of piezoelectric and ferroelectric properties of diverse materials using SPM-based methods is summarized. Among the SPM techniques, the focus is on recent studies that are related to piezoresponse force microscopy and conductive atomic force microscopy; further, the utilization of these two modes to understand piezoelectric and ferroelectric properties at the nanoscale level is discussed. This work can provide guidelines for evaluating the piezoelectric and ferroelectric properties of materials based on SPM techniques.

Mechanical-Bending-Induced Fluorescence Enhancement in Plastically Flexible Crystals of a GFP Chromophore Analogue

Single crystals of optoelectronic materials that respond to external stimuli, such as mechanical, light, or heat, are immensely attractive for next generation smart materials. Here we report single crystals of a green fluorescent protein (GFP) chromophore analogue with irreversible mechanical bending and associated unusual enhancement of the fluorescence, which is attributed to the strained molecular packing in the perturbed region. Soft crystalline materials with such fluorescence intensity modulations occurring in response to mechanical stimuli under ambient pressure conditions will have potential implications for the design of technologically relevant tunable fluorescent materials.

Engineering Mechanical Compliance of an Organic Compound toward Flexible Crystal Lasing Media

Recently, organic crystals with mechanical flexibility have been emerging as a hot research topic due to their great potentials in flexible optoelectronics. However, organic crystals exhibiting elastic bending or plastic bending are relatively rare. In this study, we proposed a strategy to improve the probability of crystal flexibility as well as to regulate the mechanical properties by controlling polymorphism. Three different emissive organic polymorphs Cry-G, Cry-Y, and Cry-O with elastic, plastic, and brittle natures, respectively, were obtained by fine-tuning crystallization conditions of a diaryl β-diketone compound. Cry-G was found to transduce light and amplify the self-waveguided emission efficiently along the crystal body in the elastically bent state, demonstrating its multifunctional applications in flexible optical devices. This study is of great scientific significance not only to engineer mechanical compliance of organic crystals but also to highlight the utility of "crystal flexibility".

Interlinker Hydrogen Bonds Govern CO2 Adsorption in a Series of Flexible 2D Diacylhydrazone/Isophthalate-Based MOFs: Influence of Metal Center, Linker Substituent, and Activation Temperature

Four new layered flexible metal–organic frameworks (MOFs) containing a diacylhydrazone moiety, namely, guest-filled [Zn₂(iso)₂(tdih)₂]_n (1), [Zn₂(NH₂iso)₂(tdih)₂]_n (2), [Cd₂(iso)₂(tdih)₂]_n (3) and [Cd₂(NH₂iso)₂(tdih)₂]_n (4) were synthesized using terephthalaldehyde di-isonicotinoylhydrazone (tdih) as a linear ditopic linker as well as isophtalate (iso) or 5-aminoisophthalate (NH₂iso) as angular colinkers. The MOFs with hexacoordinated cadmium centers feature two-dimensional pore systems as compared to the MOFs with pentacoordinated zinc centers showing either zero-dimensional or mixed zero-/one-dimensional voids, as evidenced by single-crystal X-ray diffraction. In contrast to the frameworks based on isophtalates which do not show any significant gas uptakes, introduction of amino-substituted linker enables CO₂ adsorption. Gently activated aminoisophthalate-based frameworks, that is, guest-exchanged in methanol and heated to 100 °C, show reversible gated CO₂ adsorptions at 195 K, whereas the increase of activation temperature to 150 °C or more leads to one-step isotherms and lower adsorption capacities. X-ray diffraction and IR spectroscopy reveal significant structural differences in interlayer hydrogen bonding upon activation of materials at higher temperatures. The work emphasizes the role of hydrogen bonds in crystal engineering of layered materials and the importance of activation conditions in such systems.

Interplay between a metal center and functionalization of isophthalate linker leads to remarkable diversity of structures and properties in the series of layered flexible metal−organic frameworks. Intriguing adsorption properties include stepwise gated CO₂ adsorptions and strong dependence on activation conditions. The role of hydrogen bonds in crystal engineering of layered materials is underscored by activation−structure−adsorption correlations.

Solvent-Dependent Bending Ability of Salen-Derived Organic Crystals

The formation of plastic or brittle organic crystals of salen derivatives that depend on the solvents employed for crystallization is demonstrated. Large yellow crystals (ranging from mm to cm size) of ten different salen derivatives were obtained and investigated. Among them, (bis(2-hydroxyacetophenone)ethylenediimine) 2, which was recrystallized from dichloromethane, tetrahydrofuran or chloroform, exhibited plastic deformation behaviour when mechanical force was applied to the (001) face. In contrast, when 2 was recrystallized from benzene, brittle crystals were obtained. Face indexing confirmed that different crystal faces were obtained by depending on the solvent employed for recrystallization, which leads to either flexible (plastic) or brittle crystals. Photoluminescence with a band maximum at 510 nm and thermochromism related to tautomerism between OH and NH forms were also investigated, and indicate that 2 is a flexible organic single-crystal material with multifunctional properties.

Interfacial Interaction of Absorbate Copper Phthalocyanine with PVDF Based Ferroelectric Polymer Substrates: A Spectroscopic Study

Studies of CuPc thin films on underlying ferroelectric copolymeric and terpolymeric substrates have been performed by ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Work function (WF) and highest occupied molecular orbital (HOMO) energy level shift observed from UPS spectroscopy for successive deposition of CuPc molecules on ferroelectric polymer surfaces confirm the formation of interface dipole at the CuPc-ferroelectric polymer interface owing to charge transfer from the tailing region of the CuPc HOMO density of states (DOS) to the ferroelectric polymer layer. According to our thickness dependent XPS data, CuPc molecules are coupled to the organic ferroelectric surfaces through the central metal atom of the CuPc molecules, i.e., copper atom, and the halogens of underlying ferroelectric polymer surfaces, and hence support the charge transfer phenomenon from CuPc molecules to the ferroelectric polymer substrate. Polarization dependent NEXAFS results reveal that CuPc molecules retain their tilted geometrical configuration even at submonolayer thickness of the molecular films on both ferroelectric surfaces and confirms the electronic structural disturbance associated with structural modification of CuPc molecules due to interfacial charge transfer. Therefore, the energy level alignment with increment in the thickness of CuPc films at both the organic semiconductor-ferroelectric polymer interface is controlled by the charge transfer phenomenon from deposited CuPc molecules to the organic ferroelectric substrates. Our results provide a clear understanding about chemical interactions, molecular configurations, energy level alignment, and their correlation at CuPc/polymeric ferroelectric interfaces that can be important for organic nonvolatile memory and synaptic based thin-film transistor devices.

A Mechanistic Perspective on Plastically Flexible Coordination Polymers

Mechanical flexibility in single crystals of covalently bound materials is a fascinating and poorly understood phenomenon. We present here the first example of a plastically flexible one-dimensional (1D) coordination polymer. The compound [Zn(μ-Cl)2 (3,5-dichloropyridine)2 ]n is flexible over two crystallographic faces. Remarkably, the single crystal remains intact when bent to 180°. A combination of microscopy, diffraction, and spectroscopic studies have been used to probe the structural response of the crystal lattice to mechanical bending. Deformation of the covalent polymer chains does not appear to be responsible for the observed macroscopic bending. Instead, our results suggest that mechanical bending occurs by displacement of the coordination polymer chains. Based on experimental and theoretical evidence, we propose a new model for mechanical flexibility in 1D coordination polymers. Moreover, our calculations propose a cause of the different mechanical properties of this compound and a structurally similar elastic material.

Room temperature magnetoelectric coupling in a molecular ferroelectric ytterbium(III) complex

Magnetoelectric (ME) materials combine magnetic and electric polarizabilities in the same phase, offering a basis for developing high-density data storage and spintronic or low-consumption devices owing to the possibility of triggering one property with the other. Such applications require strong interaction between the constitutive properties, a criterion that is rarely met in classical inorganic ME materials at room temperature. We provide evidence of a strong ME coupling in a paramagnetic ferroelectric lanthanide coordination complex with magnetostrictive phenomenon. The properties of this molecular material suggest that it may be competitive with inorganic magnetoelectrics.

Tuning the photomechanical behavior and excellent elasticity of azobenzene via cocrystal engineering

Obtaining crystals with different photomechanical responses and excellent mechanical properties simultaneously through cocrystal engineering based on the same photoactive molecule.

13C NMR of DIPAC and DIPAB organic ferroelectrics

The diisopropylammonium chloride (C₆H₁₆ClN, DIPAC) and diisopropylammonium bromide (C₆H₁₆BrN, DIPAB) molecular crystals are recently discovered ferroelectrics with sufficiently high spontaneous polarization and Curie temperature. We performed first studies of these crystals by ¹³C NMR. CP MAS spectra were collected within large temperature ranges covering the Curie points. The reconstructive phase transition from the initial orthorhombic P2₁2₁2₁ structure of DIPAB to the monoclinic ferroelectric P2₁ structure leads to an abrupt alteration in the ¹³C spectrum. The ¹³C spectra for DIPAC and DIPAB in the ferroelectric P2₁ phase are quite similar with four lines at lower frequencies, which correspond to the CH₃ groups, and two lines with close chemical shifts, which correspond to two CH groups. The transition into the paraphase leads to gradual reduction of the interline distances in the low-frequency quadruplet and in the doublet. The step-like changes in the interline frequency shifts at this transition indicating its first order. The analysis of the spectrum evolution in the paraphase shows that only a CH group lays in the reflection plane above the P2₁  →  P2₁/m transition, while the second CH group only moves closer to the reflection plane upon further heating.

An Organic Crystal with High Elasticity at an Ultra-Low Temperature (77 K) and Shapeability at High Temperatures

Organic single crystals with elastic bending capability and potential applications in flexible devices and sensors have been elucidated. Exploring the temperature compatibility of elasticity is essential for defining application boundaries of elastic materials. However, related studies have rarely been reported for elastic organic crystals. Now, an organic crystal displays elasticity even in liquid nitrogen (77 K). The elasticity can be maintained below ca. 150 °C. At higher temperatures, the heat setting property enables us to make various shapes of crystalline fibers based on this single kind of crystal. Through detailed crystallographic analyses and contrast experiments, the mechanisms behind the unusual low-temperature elasticity and high-temperature heat setting are disclosed.

Intermolecular Interactions in Functional Crystalline Materials: From Data to Knowledge

Intermolecular interactions of organic, inorganic, and organometallic compounds are the key to many composition–structure and structure–property networks. In this review, some of these relations and the tools developed by the Cambridge Crystallographic Data Center (CCDC) to analyze them and design solid forms with desired properties are described. The potential of studies supported by the Cambridge Structural Database (CSD)-Materials tools for investigation of dynamic processes in crystals, for analysis of biologically active, high energy, optical, (electro)conductive, and other functional crystalline materials, and for the prediction of novel solid forms (polymorphs, co-crystals, solvates) are discussed. Besides, some unusual applications, the potential for further development and limitations of the CCDC software are reported.

Record-high thermal stability achieved in a novel single-component all-organic ferroelectric crystal exhibiting polymorphism

Traditionally, lead and heavy metal containing inorganic oxides dominate the area of ferroelectricity. Although, recently, lightweight non-toxic organic ferroelectrics have emerged as excellent alternatives, achieving higher temperature up to which the ferroelectric phase can persist has remained a challenge. Moreover, only a few of those are single-component molecular ferroelectrics and were discovered upon revisiting their crystal structures. Here we report a novel phenanthroimidazole derivative, which not only displays notable spontaneous and highly stable remnant polarizations with a low coercive field but also retains its ferroelectric phase up to a record-high temperature of ∼521 K. Subsequently, the crystal undergoes phase transition to form non-polar and centrosymmetric polymorphs, the first study of its kind in a single-component ferroelectric crystal. Moreover, the compound exhibits a significantly high thermal stability. Given the excellent figures-of-merit for ferroelectricity, this material is likely to find potential applications in microelectronic devices pertaining to non-volatile memory.

Shape-memory effects in molecular crystals

Molecular crystals can be bent elastically by expansion or plastically by delamination into slabs that glide along slip planes. Here we report that upon bending, terephthalic acid crystals can undergo a mechanically induced phase transition without delamination and their overall crystal integrity is retained. Such plastically bent crystals act as bimorphs and their phase uniformity can be recovered thermally by taking the crystal over the phase transition temperature. This recovers the original straight shape and the crystal can be bent by a reverse thermal treatment, resulting in shape memory effects akin of those observed with some metal alloys and polymers. We anticipate that similar memory and restorative effects are common for other molecular crystals having metastable polymorphs. The results demonstrate the advantage of using intermolecular interactions to accomplish mechanically adaptive properties with organic solids that bridge the gap between mesophasic and inorganic materials in the materials property space.

Molecular crystals can be bent elastically by expansion or contraction on opposite faces, or plastically by delamination into slabs that glide along slip planes. Here the authors report crystals that can be bent plastically while undergoing a mechanically induced phase transition without delamination.

Mechanically interlocked architecture aids an ultra-stiff and ultra-hard elastically bendable cocrystal

Molecular crystals are not known to be as stiff as metals, composites and ceramics. Here we report an exceptional mechanical stiffness and high hardness in a known elastically bendable organic cocrystal [caffeine (CAF), 4-chloro-3-nitrobenzoic acid (CNB) and methanol (1:1:1)] which is comparable to certain low-density metals. Spatially resolved atomic level studies reveal that the mechanically interlocked weak hydrogen bond networks which are separated by dispersive interactions give rise to these mechanical properties. Upon bending, the crystals significantly conserve the overall energy by efficient redistribution of stress while perturbations in hydrogen bonds are compensated by strengthened π-stacking. Furthermore we report a remarkable stiffening and hardening in the elastically bent crystal. Hence, mechanically interlocked architectures provide an unexplored route to reach new mechanical limits and adaptability in organic crystals. This proof of concept inspires the design of light-weight, stiff crystalline organics with potential to rival certain inorganics, which currently seem inconceivable.

Quantitative Electromechanical Atomic Force Microscopy

The ability to probe a material's electromechanical functionality on the nanoscale is critical to applications from energy storage and computing to biology and medicine. Voltage-modulated atomic force microscopy (VM-AFM) has become a mainstay characterization tool for investigating these materials due to its ability to locally probe electromechanically responsive materials with spatial resolution from micrometers to nanometers. However, with the wide popularity of VM-AFM techniques such as piezoresponse force microscopy and electrochemical strain microscopy there has been a rise in reports of nanoscale electromechanical functionality, including hysteresis, in materials that should be incapable of exhibiting piezo- or ferroelectricity. Explanations for the origins of unexpected nanoscale phenomena have included new material properties, surface-mediated polarization changes, and/or spatially resolved behavior that is not present in bulk measurements. At the same time, it is well known that VM-AFM measurements are susceptible to numerous forms of crosstalk, and, despite efforts within the AFM community, a global approach for eliminating this has remained elusive. In this work, we develop a method for easily demonstrating the presence of hysteretic (i.e., "false ferroelectric") long-range interactions between the sample and cantilever body. This method should be easy to implement in any VM-AFM measurement. We then go on to demonstrate fully quantitative and repeatable nanoelectromechanical characterization using an interferometer. These quantitative measurements are critical for a wide range of devices including MEMS actuators and sensors, memristor, energy storage, and memory.

A Million Crystal Structures: The Whole Is Greater than the Sum of Its Parts

The founding in 1965 of what is now called the Cambridge Structural Database (CSD) has reaped dividends in numerous and diverse areas of chemical research. Each of the million or so crystal structures in the database was solved for its own particular reason, but collected together, the structures can be reused to address a multitude of new problems. In this Review, which is focused mainly on the last 10 years, we chronicle the contribution of the CSD to research into molecular geometries, molecular interactions, and molecular assemblies and demonstrate its value in the design of biologically active molecules and the solid forms in which they are delivered. Its potential in other commercially relevant areas is described, including gas storage and delivery, thin films, and (opto)electronics. The CSD also aids the solution of new crystal structures. Because no scientific instrument is without shortcomings, the limitations of CSD research are assessed. We emphasize the importance of maintaining database quality: notwithstanding the arrival of big data and machine learning, it remains perilous to ignore the principle of garbage in, garbage out. Finally, we explain why the CSD must evolve with the world around it to ensure it remains fit for purpose in the years ahead.

Is a Bent Crystal Still a Single Crystal?

The mention of the word "crystal" invokes images of minerals, gems, and rocks, all of which are inevitably solid, hard, and durable entities with well-defined smooth faces and straight edges. With the discovery in the first half of the 20th century that many molecular crystals are soft and can be deformed in a similar way as rubber or plastic, this perception is changing, and both the concept and formal definition of what a crystal is may require reinterpretation. The seemingly naïve question posed in the title of this Minireview does not have a simple answer. Here, we discuss how the effects of the elastic and plastic deformation of molecular crystals on the diffraction signature give primary evidence of their degree of crystallinity. In most cases, the definition of a crystal holds for both elastically and plastically deformed crystals and, unless there is significant or complete physical separation of the crystal during the deformation, they can safely be considered (deformed) single crystals with a high concentration of defects.

Red-Emissive Organic Crystals of a Single-Benzene Molecule: Elastically Bendable and Flexible Optical Waveguide

Organic crystals are easily cracked into pieces or powders under applied stress because of their intrinsic brittle nature. This undesired mechanical property directly limits their application in flexible optical and optoelectronic devices. Herein, we developed a compact single-benzene molecule dimethyl 2,5-bis((2-hydroxyethyl)amino)terephthalate, which was easily crystallized to form two polymorphs, A and B. Featuring a single-benzene π-system, both polymorphs A and B display red fluorescence in crystals. More importantly, crystals of polymorph A are flexible and can be elastically bent under mechanical force. Given these advantages, a flexible optical waveguide has been realized in the crystal of polymorph A with a bent shape, highlighting its potential application in flexible devices. In addition, the thermal transformation of crystals from polymorph A to polymorph B, which was accompanied by the change of optical property as well as mechanical elasticity, has been observed.

Flexible, Temperature-Resistant, and Fatigue-Free Ferroelectric Memory Based on Bi(Fe0.93Mn0.05Ti0.02)O3 Thin Film

A recent hot-spot topic for flexible and wearable devices involves high-performance nonvolatile ferroelectric memories operating under compressive or tensile mechanical deformations. This work presents the direct fabrication of a flexible (Mn,Ti)-codoped multiferroic BiFeO₃ film capacitor with Pt bottom and Au top electrodes on mica substrate. The fabricated polycrystalline Bi(Fe_0.93Mn_0.05Ti_0.02)O₃ film on mica exhibits superior ferroelectric switching behavior with robust saturated polarization ( P_s ∼ 93 μC/cm²) and remanent polarization ( P_r ∼ 66 μC/cm²) and excellent frequency stability (1-50 kHz) and temperature resistance (25-200 °C), as well as reliable long-lifetime operation. More saliently, it can be safely bent to a small radius of curvature, as low as 2 mm, or go through repeated compressive/tensile mechanical flexing for 10³ bending times at 4 mm radius without any obvious deterioration in polarization, retention time at 10⁵ s, or fatigue resistance after 10⁹ switching cycles. These findings demonstrate a novel route to designing flexible BiFeO₃-based ferroelectric memories for information storage and data processing, with promising applications in next-generation smart electronics.

Bloch Oscillations in Fibonacci lattices: polaron formation

We investigated the dynamics of an electron subjected to a uniform electric field in the scope of a tight-binding electron-phonon interacting approach. We aimed at describing the transport in a one-dimensional lattice in which the on-site energies are distributed according to a Fibonacci sequence. Within this physical picture, we obtained a novel dynamical process with no counterpart in ordered lattices. Our findings showed that in low-disorder limit, the electron performs spatial Bloch oscillations, generating, in the turning points of its trajectory, composite quasi-particles-namely, polarons. When it comes to highly disordered systems, two strongly localized polarons are formed in the region where the oscillating charge is confined, thus propagating excitations that are present in the lattice.

Ultralarge Dielectric Relaxation and Self-Recovery Triggered by Hydrogen-Bonded Polar Components

Subtle integration of rotatable polar components into dielectric crystals can contribute significantly to adjustable switching temperatures ( T_s) and dielectric relaxation behaviors. Currently, one of the biggest challenges lies in the design of optimal polar components with moderate motion resistance in a crystalline system. In this work, we demonstrate that under refrigerator conditions, rotatable hydrogen-bonded one-dimensional (1D) cationic chains, {[C₂H₆N₅]⁺} _n (C₂H₆N₅ = 3,5-diamino-1,2,4-triazolinium), and two-dimensional (2D) anionic layers, {[(H₂O)₂·SO₄]^2-} _n, can be generated in an organic salt, 3 ([C₂H₆N₅]₂·[(H₂O)₂·SO₄]). Compared with the nonhydrated precursor, 2 ([C₂H₇N₅]·[SO₄]), the rotation of these 1D and 2D ionic species triggers a reversible phase transition and dielectric switching in 3. In addition, the significantly sluggish rotation of the 1D cationic chains from parallel to unparallel stacking and the counter-clockwise rotation of the 2D anionic layers, compared with their reverse processes, induce a frequency-dependent dielectric response with a more highly adjustable heating T_s↑ than the cooling T_s↓. More importantly, 3 possesses excellent self-recovery ability attributed to the highly dynamic character of the hydrogen-bonded ionic species. The strategy here can provide a fairly good model for designing dielectric crystals with desired rotatable polar components.

Metal–Organic Frameworks (MOFs) as Potential Hybrid Ferroelectric Materials

This chapter presents new findings of intrinsic and induced ferroelectricity in Metal–Organic Frameworks (MOFs) with a polar system, capable of forming an electronic structure in an asymmetric lattice. Multiple experimental techniques and simulation methods are reviewed in detail. The characteristics of ferroelectrics such as discontinuity in temperature-dependent dielectric constant, polarization hysteresis loops, etc. have been observed from several MOF large crystals and crystalline powders. A relationship between polarization and bond polarity for MOFs has been established. In addition, we emphasize the significance of mechanical strength of MOFs in real applications. This chapter reviews MOF materials for energy storage and utilization, aiming to provide an insight into the design of novel MOF-based ferroelectrics.

Bromine–bromine interactions enhanced plasticity for the bending of a single crystal without affecting fluorescent properties

The crystal plasticity, due to bromine–bromine interactions, plays a crucial role in generating a slip plane and thus, under mechanical force, crystals undergo bending without affecting their fluorescent properties.

Hierarchical Frameworks of Metal-Organic Cages with Axial Ferroelectric Anisotropy

Designing molecular crystals with switchable dipoles for ferroelectric applications is challenging and often serendipitous. Herein, we show a systematic approach toward hierarchical 1D, 2D and 3D frameworks that are assembled through successive linkage of metal-organic cages [Cu₆ (H₂ O)₁₂ (TPTA)₈ ]¹²⁺ with chloride ions. Their ferroelectric properties are due to the displacement of channel-bound nitrate counterions and solvated water molecules relative to the framework of cages. Ferroelectric measurements of crystals of discrete and 1D-framework assemblies showed axial ferroelectric anisotropy with high remnant polarisation. Both, the reversible formation of cage-connected networks and the observation of ferroelectric anisotropic behaviour are rare among metal-ligand cage assemblies.

Dislocations in molecular crystals

Dislocations in molecular crystals remain terra incognita. Owing to the complexity of molecular structure, dislocations in molecular crystals can be difficult to understand using only the foundational concepts devised over decades for hard materials. Herein, we review the generation, structure, and physicochemical consequences of dislocations in molecular crystals. Unlike metals, ceramics, and semiconductors, molecular crystals are often characterized by flexible building units of low symmetry, thereby limiting analysis, complicating modeling, and prompting new approaches to elucidate their role in crystallography from growth to mechanics. Such considerations affect applications ranging from plastic electronics and mechanical actuators to the tableting of pharmaceuticals.

Field-Induced Antipolar-Polar Structural Transformation and Giant Electrostriction in Organic Crystal

The field-induced antipolar-polar structural transition in an organic antiferroelectric 2-trifluoromethylnaphthimidazole crystal is investigated by performing synchrotron X-ray diffraction. The polarities of all of the hydrogen-bonded chains become parallel with each other in the presence of an external electric field. The switching is accompanied by a giant electrostriction, which provides 1 order of magnitude larger strain than the piezoelectric strain of the organic ferroelectrics: croconic acid and poly(vinylidene fluoride); however, it is comparable to those of typical commercial piezoelectric ceramics. The crystal structure analysis with electric field shows that the origin of the observed giant electrostriction can be attributed to the shear strain that emerges from the polarity switching of the hydrogen-bonded chains. The antipolar-polar structural transition in antiferroelectrics could be employed for the development of high-performance electrostrictive organic materials.

Recent Advances of Flexible Data Storage Devices Based on Organic Nanoscaled Materials

Following the trend of miniaturization as per Moore's law, and facing the strong demand of next-generation electronic devices that should be highly portable, wearable, transplantable, and lightweight, growing endeavors have been made to develop novel flexible data storage devices possessing nonvolatile ability, high-density storage, high-switching speed, and reliable endurance properties. Nonvolatile organic data storage devices including memory devices on the basis of floating-gate, charge-trapping, and ferroelectric architectures, as well as organic resistive memory are believed to be favorable candidates for future data storage applications. In this Review, typical information on device structure, memory characteristics, device operation mechanisms, mechanical properties, challenges, and recent progress of the above categories of flexible data storage devices based on organic nanoscaled materials is summarized.

Bioinspired Flexible and Tough Layered Peptide Crystals

One major challenge of functional material fabrication is combining flexibility, strength, and toughness. In several biological and artificial systems, these desired mechanical properties are achieved by hierarchical architectures and various forms of anisotropy, as found in bones and nacre. Here, it is reported that crystals of N-capped diphenylalanine, one of the most studied self-assembling systems in nanotechnology, exhibit well-ordered packing and diffraction of sub-Å resolution, yet display an exceptionally flexible nature. To explore this flexibility, the mechanical properties of individual crystals are evaluated, assisted by density functional theory calculations. High-resolution scanning electron microscopy reveals that the crystals are composed of layered self-assembled structures. The observed combination of strength, toughness, and flexibility can therefore be explained in terms of weak interactions between rigid layers. These crystals represent a novel class of self-assembled layered materials, which can be utilized for various technological applications, where a combination of usually contradictory mechanical properties is desired.

Morpholinium chloroindate(iii) complex: a rare acentric structural arrangement leading to piezoelectric properties

In(iii)-Based morpholinium complex, [C4H10NO]+[InCl5(C4H10NO)]−: crystal structure, origin of the structure polarity, and evidence of piezoelectric properties.

Ferroelectricity and Piezoelectricity in Free-Standing Polycrystalline Films of Plastic Crystals

Plastic crystals represent a unique compound class that is often encountered in molecules with globular structures. The highly symmetric cubic crystal structure of plastic crystals endows these materials with multiaxial ferroelectricity that allows a three-dimensional realignment of the polarization axes of the crystals, which cannot be achieved using conventional molecular ferroelectric crystals with low crystal symmetry. In this work, we focused our attention on malleability as another characteristic feature of plastic crystals. We have synthesized the new plastic/ferroelectric ionic crystals tetramethylammonium tetrachloroferrate(III) and tetramethylammonium bromotrichloroferrate(III), and discovered that free-standing translucent films can be easily prepared by pressing powdered samples of these compounds. The thus obtained polycrystalline films exhibit ferroelectric polarization switching and a relatively large piezoelectric response at room temperature. The ready availability of functional films demonstrates the practical utility of such plastic/ferroelectric crystals, and considering the vast variety of possible constituent cations and anions, a wide range of applications should be expected for these unique and attractive functional materials.

Synergistic Configuration of Diols as Brønsted Bases

As viscous hydroxylic organic compounds, diols are of interest for their functional molecular conformation, which is based on inter- and intramolecular hydrogen (H)-bonds. By utilising steady-state electronic and vibrational spectroscopy, time-resolved fluorescence spectroscopy, and computational analyses, we report the association of the hydroxyl groups of diols via intra- or intermolecular H-bonds to enhance their reactivity as a base. Whereas the formation of an intermolecularly H-bonded dimer is requisite for diols of weak intramolecular H-bond to extract a proton from a model strong photoacid, a well-configured single diol molecule with an optimised intramolecular H-bond is revealed to serve as an effective Brønsted base with increased basicity. This observation highlights the collective role of H-bonding in acid-base reactions, and provides mechanistic backgrounds to understand the reactivity of polyols in the acid-catalysed dehydration for the synthesis of cyclic ethers at the molecular level.