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Shape memory alloys have been used extensively in actuators, couplings, medical guide wires, and smart devices, because of their unique shape memory effect and superelasticity triggered by the reversible martensitic phase transformations. For ferroic materials, however, almost no memory effects have been found for their ferroic domains after reversible phase transformations. Here, we present a pair of single-component organic enantiomorphic ferroelectric/ferroelastic crystals, (R)- and (S)-N-3,5-di-tert-butylsalicylidene-1-(1-naphthyl)ethylamine SA-NPh-(R) and SA-NPh-(S). It is notable that not only can their ferroic domain patterns disappear and reappear during reversible thermodynamic phase transformations, but they can also disappear and reappear during reversible light-driven phase transformations induced by enol-keto photoisomerization, both of which are from P1 to P2 1 polar space groups. Most importantly, the domain patterns are exactly the same in the initial and final states, demonstrating the existence of a memory effect for the ferroic domains in SA-NPh-(R) and SA-NPh-(S). As far as we are aware, the domain memory effect triggered by both thermodynamic and light-driven ferroelectric/ferroelastic phase transformations remains unexplored in ferroic materials. Thermal and optical control of domain memory effect would open up a fresh research field for smart ferroic materials., (© 2022. The Author(s).)

Organic single-component ferroelectrics, as an important class of metal-free ferroelectrics, are highly desirable because of their easy processing, mechanical flexibility, and biocompatibility. However, although nearly 50 years have passed since the discovery of photochromism in azobenzene-doped cholesteric liquid crystals, ferroelectricity has never been found in azobenzene-based crystals. Here, we use an amino group to substitute a fluorine atom of 2,2',4,4',6,6'-hexafluoroazobenzene, which successfully introduces ferroelectricity into 2-amino-2',4,4',6,6'-pentafluoroazobenzene (APFA). APFA shows an extremely high Curie temperature ( T c ) of 443 K, which is outstanding among single-component ferroelectrics. It also exhibits an indirect optical band gap of 2.27 eV as well as photoisomerization behavior between the trans -form and the cis -form triggered by pedal motion. To our knowledge, APFA is the first azobenzene-based ferroelectric crystal. This work opens an avenue to design excellent single-component ferroelectrics and will inspire the exploration of azobenzene-based ferroelectrics for promising applications in biofriendly ferroelectric devices., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

A four-ingredient polymer chain has record-breaking piezoelectric capability.

A ferroelectric/ferroelastic is a material whose spontaneous polarization/strain can be switched by applying an external electric field/mechanical stress. However, the optical control of spontaneous polarization/strain remains relatively unexplored in crystalline materials, although photoirradiation stands out as a nondestructive, noncontact, and remote-controlled stimulus beyond stress or electric field. Here, we present two new organic single-component homochiral photochromic multiferroics, ( R )- and ( S )- N -3,5-di- tert -butylsalicylidene-1-4-bromophenylethylamine (SA-Ph-Br( R ) and SA-Ph-Br( S )), which show a full ferroelectric/ferroelastic phase transition of 222F2 type at 336 K. Under photoirradiation, their spontaneous polarization/strain can be switched quickly within seconds and reversibly between two ferroelectric/ferroelastic phases with the respective enol and trans -keto forms triggered by structural photoisomerizations. In addition, they possess a superior acoustic impedance characteristic with a value of ∼2.42 × 10 6 kg·s -1 ·m -2 , lower than that of polyvinylidene fluoride (PVDF, (3.69-4.25) × 10 6 kg·s -1 ·m -2 ), which can better match human tissues. This work realizes for the first time that multiple ferroic orders in single-component organic crystals with ultralow acoustic impedance can be simultaneously controlled and coupled by three physical channels (electric, stress, light fields), suggesting their great potential in multichannel data storage, optoelectronics, and related applications compatible with all-organic electronics and human tissues.

Ferroelectrics usually exhibit temperature-triggered structural changes, which play crucial roles in controlling their physical properties. However, although light is very striking as a non-contact, non-destructive, and remotely controlled external stimuli, ferroelectric crystals with light-triggered structural changes are very rare, which holds promise for optical control of ferroelectric properties. Here, an organic molecular ferroelectric, N-salicylidene-2,3,4,5,6-pentafluoroaniline (SA-PFA), which shows light-triggered structural change of reversible photoisomerization between cis-enol and trans-keto configuration is reported. SA-PFA presents clear ferroelectricity with the saturate polarization of 0.84 μC cm -2 , larger than those of some typical organic ferroelectrics with thermodynamically structural changes. Benefit from the reversible photoisomerization, the dielectric real part of SA-PFA can be reversibly switched by light. More strikingly, the photoisomerization enables SA-PFA to show reversible optically induced ferroelectric polarization switching. Such intriguing behaviors make SPFA a potential candidate for application in next-generation photo-controlled ferroelectric devices. This work sheds light on further exploration of more excellent molecular ferroelectrics with light-triggered structural changes for optical control of ferroelectric properties., (© 2021 The Authors. Advanced Science published by Wiley-VCH GmbH.)

With prosperity, decay, and another spring, molecular ferroelectrics have passed a hundred years since Valasek first discovered ferroelectricity in the molecular compound Rochelle salt. Recently, the proposal of ferroelectrochemistry has injected new vigor into this century-old research field. It should be highlighted that piezoresponse force microscopy (PFM) technique, as a non-destructive imaging and manipulation method for ferroelectric domains at the nanoscale, can significantly speed up the design rate of molecular ferroelectrics as well as enhance the ferroelectric and piezoelectric performances relying on domain engineering. Herein, we provide a brief review of the contribution of the PFM technique toward assisting the design and performance optimization of molecular ferroelectrics. Relying on the relationship between ferroelectric domains and crystallography, together with other physical characteristics such as domain switching and piezoelectricity, we believe that the PFM technique can be effectively applied to assist the design of high-performance molecular ferroelectrics equipped with multifunctionality, and thereby facilitate their practical utilization in optics, electronics, magnetics, thermotics, and mechanics among others.

The well-developed design strategy of molecular modification for assembling molecular ferroelectrics mainly focuses on the cations. Herein, by homochiral anionic modification of the non-ferroelectric (quinuclidinium)(HSO 4 ), we designed high-temperature multiaxial organic enantiomeric ferroelectrics, (quinuclidinium)(l- and d-camphorsulfonate). This work paves a new road for precisely constructing excellent molecular ferroelectrics.

Objective: Bladder urothelial carcinoma (BUC) is a common urological malignancy with molecular heterogeneity. However, the genetic feature of Chinese BUC patients is still not well-identified., Methods: We performed deep sequencing by a large panel (450 genes) on 22 BUC samples and using matched normal bladder tissue as control. Genomic alterations (GAs), pathways and Tumor Mutation Burden (TMB) were investigated., Results: The frequencies of GAs ( TERT , 54.5%; CREBBP , 27.3%; GATA3 , 22.7%; BRAF , 18.2%; TEK , 18.2% and GLI1 , 18.2%) were significantly higher in Chinese than Western BUC patients. Other GAs' frequencies were in accordance with previous study ( TP53 , 50.0%; KDM6A , 31.8%; KMT2D , 22.7%; etc.). Besides, we detected gene amplification in ERBB2, FRS2, FAS , etc. The gene fusion/rearrangement took place in the chromosome 11, 12, 14, 17, 19, 22, and Y. Other than cell cycle and PI3K-AKT-mTOR, mutated genes were more associated with the transcription factor, chromatin modification signaling pathways. Interestingly, the TMB value was significantly higher in the BUC patients at stages T1-T2 than T3-T4 ( P = 0.025)., Conclusion: Deep genomic sequencing of BUC can provide new clues on the unique GAs of Chinese patients and assist in therapeutic decision., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Li, Yang, Liao, Zhou, Li, Cai, Liu, Luo and Zhan.)

Organic-inorganic metal halide ferroelectric semiconductors are mainly lead halide ones, suffering from the presence of toxic lead. Herein, we report a lead-free bismuth iodide ferroelectric semiconductor [1,4-butanediammonium]BiI5, showing a high Curie temperature of 365 K and a small band gap of 1.95 eV, smaller than those of most lead halide counterparts.

Organic ferroelectrics are attracting tremendous interest because of their mechanical flexibility, ease of fabrication, and low acoustical impedance. Although great advances have been made in recent years, topological defects such as vortices remain relatively unexplored in the organic ferroelectric system. Here, from [quinuclidinium]ReO 4 ([Q]ReO 4 ), we applied the molecular design strategy of H/F substitution to successfully synthesize the organic ferroelectric [4-fluoroquinuclidinium]ReO 4 ([4-F-Q]ReO 4 ). Through H/F substitution, the Curie temperature and spontaneous polarization are respectively increased from 367 K and 5.83 μC/cm 2 in [Q]ReO 4 to 466 K and 11.37 μC/cm 2 in [4-F-Q]ReO 4 . Moreover, under mechanical stress fields, three kinds of stripelike domains with various polarization directions emerge to form a windmill-like domain pattern in the thin film of [4-F-Q]ReO 4 , in which intriguing vortex-antivortex topological configurations can exist stably. This work provides an efficient strategy for optimizing the properties of organic ferroelectrics and exploring emergent phenomena.

The nonradiative recombination of electrons and holes has been identified as the main cause of energy loss in hybrid organic-inorganic perovskite solar cells (PSCs). Sufficient built-in field and defect passivation can facilitate effective separation of electron-hole pairs to address the crucial issues. For the first time, we introduce a homochiral molecular ferroelectric into a PSC to enlarge the built-in electric field of the perovskite film, thereby facilitating effective charge separation and transportation. As a consequence of similarities in ionic structure, the molecular ferroelectric component of the PSC passivates the defects in the active perovskite layers, thereby inducing an approximately eightfold enhancement in photoluminescence intensity and reducing electron trap-state density. The photovoltaic molecular ferroelectric PSCs achieve a power conversion efficiency as high as 21.78 %., (© 2020 Wiley-VCH GmbH.)

Through the strategy of F/H substitution, we precisely designed the highest-Tc (phase transition temperature) organic enantiomeric ferroelectrics, (R)- and (S)-(N,N-dimethyl-3-fluoropyrrolidinium) iodide, of which the Tc reaches up to 470 K, far beyond those of other enantiomeric ferroelectrics and also the commercial ferroelectric BaTiO3.

Switchable materials play an invaluable role in signal processing and encryption of smart devices. The development of multifunctional materials that exhibit switching characteristics in multiple physical channels has attracted widespread attention. Now, two chiral thermochromic ferroelastic crystals (S-CTA) 2 CuCl 4 and (R-CTA) 2 CuCl 4 (CTA=3-chloro-2-hydroxypropyltrimethylammonium) have been prepared with switchable properties in dielectricity, conductivity, second harmonic generation (SHG), piezoelectricity, ferroelasticity, chiral, and thermochromic properties. Compared with traditional phase-transition materials with switching features, thermochromism brings additional spectral encryption possibilities for future information processing. To the best of our knowledge, this is the first chiral thermochromic ferroelastic that exhibits switching properties in seven physical channels. This work is expected to promote further exploration of multifunctional molecular switchable materials., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Chiral organic-inorganic perovskites (COIPs) have recently attracted increasing interest due to their unique inherent chirality and potential applications in next-generation optoelectronic and spintronic devices. However, COIP ferroelectrics are very sparse. In this work, for the first time, we present the nickel-nitrite ABX 3 COIP ferroelectrics, [( R and S )- N -fluoromethyl-3-quinuclidinol]Ni(NO 2 ) 3 ([( R and S )-FMQ]Ni(NO 2 ) 3 ), where the X-site is the rarely seen NO 2 - bridging ligand. [( R and S )-FMQ]Ni(NO 2 ) 3 display mirror-relationship in the crystal structure and vibrational circular dichroism signal. It is emphasized that [( R and S )-FMQ]Ni(NO 2 ) 3 show splendid ferroelectricity with both an extremely high phase-transition point of 405 K and a spontaneous polarization of 12 μC/cm 2 . To our knowledge, [( R and S )-FMQ]Ni(NO 2 ) 3 are the first examples of nickel-nitrite based COIP ferroelectrics. This finding expands the COIP family and throws light on exploration of high-performance COIP ferroelectrics.

Organic-inorganic ABX 3 (A, B = cations, X = anion) hybrids with perovskite structure have recently attracted tremendous interest due to their structural tunability and rich functional properties, such as ferroelectricity. However, ABX 3 hybrid ferroelectrics with other structures have rarely been reported. Here, we successfully designed an ABX 3 hybrid ferroelectric [(CH 3 ) 3 NCH 2 F]ZnCl 3 with a spontaneous polarization of 4.8 μC/cm 2 by the molecular modification of [(CH 3 ) 4 N]ZnCl 3 through hydrogen/halogen substitution. It is the first zinc halide ABX 3 ferroelectric, which contains one-dimensional [ZnCl 3 ] - n chains of corner-sharing ZnCl 4 tetrahedra, distinct from the anionic framework of corner-sharing or face-sharing BX 6 octahedra in the ABX 3 perovskites. From zero dimension to one dimension, the high symmetry of ZnCl 4 tetrahedra is broken, and all of them align along one direction to form a polar [ZnCl 3 ] - n chain, beneficial to the generation of ferroelectricity. This finding provides an efficient polar anionic framework for enriching the family of hybrid ferroelectrics by assembling with various cations and should inspire further exploration of new classes of organic-inorganic ABX 3 ferroelectrics.

Three-dimensional (3D) organic-inorganic lead halides represented by [CH 3 NH 3 ]PbI 3 perovskite have attracted great interest for their diverse functional properties and promising optoelectronic applications. However, 3D lead halides are still very rare and their ferroelectricity remains controversial. Here, we report an unprecedented 3D lead halide perovskite-related ferroelectric [2-trimethylammonioethylammonium]Pb 2 Cl 6 ([TMAEA]Pb 2 Cl 6 ), which contains a 3D lead chloride framework of corner- and edge-sharing PbCl 6 octahedral, with the [TMAEA] + cations occupying the voids of the framework. [TMAEA]Pb 2 Cl 6 shows a ferroelectric-to-paraelectric phase transition with the Curie temperature as high as 412 K, a typical ferroelectric hysteresis loop at 293 K with a spontaneous polarization of 1 μC/cm 2 , and a clear ferroelectric domain switching. To the best of our knowledge, [TMAEA]Pb 2 Cl 6 is the first 3D lead halide showing such an excellent ferroelectricity. Additionally, it also exhibits a semiconducting property with a direct band gap of 3.43 eV. This finding enriches the family of 3D hybrid lead halides and inspires the exploration of 3D lead halide ferroelectrics.

Molecular ferroelectrics have attracted considerable interests because of their easy and environmentally friendly processing, low acoustical impedance and mechanical flexibility. Herein, a molecular thermochromic ferroelectric, N,N'-dimethyl-1,4-diazoniabicyclo[2.2.2]octonium tetrachlorocuprate(II) ([DMe-DABCO]CuCl 4 ) is reported, which shows both excellent ferroelectricity and intriguing thermochromism. [DMe-DABCO]CuCl 4 undergoes a ferroelectric phase transition from Pca2 1 to Pbcm at a significantly high Curie temperature of 413 K, accompanied by a color change from yellow to red that is due to the remarkable deformation of [CuCl 4 ] 2- tetrahedron, where the ferroelectric and paraelectric phases correspond to yellow and red, respectively. Combined with multiple bistable physical properties, [DMe-DABCO]CuCl 4 would be a promising candidate for next-generation smart devices, and should inspire further exploration of multifunctional molecular ferroelectrics., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Since the first perovskite CaTiO 3 was discovered in 1839, the development of perovskite has a history of 180 years. The emergence of solar cells (CH 3 NH 3 )PbI 3 has set off the trend of hybrid organic-inorganic perovskite (HOIP) materials. Since then, various HOIPs have sprung up and been widely used in various material devices. Among them, HOIP ferroelectrics have gained widespread attention. However, antiperovskite, as a twin brother of perovskite, has been neglected although it has similar structure with perovskite. Here, we successfully found that [C 3 H 7 FN] 3 [SnCl 6 ]Cl has a three-dimensional (3D) antiperovskite structure with the formula M 3 AB. Importantly, the compound exhibits obvious ferroelectric properties with an Aizu notation of 622F6 at 391 K. To the best of our knowledge, this is the first 3D hybrid organic-inorganic antiperovskite ferroelectric, which will greatly promote the development of antiperovskite families with more superior physical properties., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Two-dimensional (2D) organic-inorganic perovskites (OIPs), with improved material stability over their 3D counterparts, are highly desirable for device applications. It is their considerable structural diversity that offers an unprecedented opportunity to engineer materials with fine-tuning functionalities. The isosteric substitution of hydrogen by an electronegative fluorine atom has been proposed as a useful route to improve the photovoltaic performance of 2D OIPs, whereas its valuable role in developing ferroelectricity is still waiting for further exploration. Herein, for the first time we applied fluorinated aromatic cations in extending the family of 2D OIP ferroelectrics, and successfully obtained [2-fluorobenzylammonium] 2 PbCl 4 as a high-performance ferroelectric semiconductor. The failures in the nonferroelectric [4-fluorobenzylammonium] 2 PbCl 4 and [3-fluorobenzylammonium] 2 PbCl 4 demonstrate that the selective introduction of fluorine in correct structural positions is particularly essential. This work represents an unprecedented proof-of-concept in the use of fluorinated aromatic cations for the targeted design of excellent 2D OIP ferroelectrics, and is believed to inspire the future development of low-cost, high-efficiency, and stable device applications.

Molecular optical-dielectric duple bistable switches are photoelectric (dielectric and fluorescent) multifunctional materials that can simultaneously convert optical and electrical signals in one device for seamless integration. However, exploring optical-dielectric duple channels of dielectric and photoluminescence is still a bigger challenge than single dielectric or photoluminescence bistable ones, which are hardly reported but probably will be heavily researched owing to the new generation artificial intelligence development needs in the future. Herein, a new optical-dielectric duple bistable switches material, [(CH 3 ) 3 NCH 2 CH 3 ] 2 MnCl 4 (I), was obtained by a simple method for volatilization of solvents. Variable temperature single crystal X-ray analysis indicates that material I has a reversible bistable structure (order-disorder structure phase transition) corresponding to switching "ON'' and "OFF''. Unlike the single dielectric bistable structures that were previously reported, material I also own bistable features in terms of fluorescence property. This material enriches the specific examples of photoelectric duple function switch materials and facilitates the development of required devices., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In this paper, three zero-dimensional organic-inorganic hybrid compounds [(CH 3 ) 3 S] 2 [CdBr 4 ] (1), [(CH 3 ) 3 S] 2 [MnBr 4 ] (2) and [(CH 3 ) 3 S] 2 [ZnBr 4 ] (3) were synthesized. The phase transition behavior of 1, 2 and 3 was well characterized by differential scanning calorimetry (DSC) and variable temperature single crystal diffraction measurements. The phase transition temperature of 1, 2 and 3 was at ca. 315 K in the heating process. The vigorous ordered-disordered reorientation and displacement motion of [(Me 3 ) 3 S] + and [MBr 4 ] 2- of 1, 2 and 3 induce the structural phase transition from the centrosymmetric (CS) space group Pnma to the non-centrosymmetric (NCS) space group P2 1 2 1 2 1 . The apparent second-harmonic generation (SHG) switching responses further confirm this CS to NCS symmetry breaking. Moreover, dielectric studies illustrate that 1, 2 and 3 display distinctly switchable dielectric behavior, revealing their potential application in dielectric switches. This finding suggests that sulfonium-based organic-inorganic hybrids can be used to build phase transition materials, broadening the way for exploring dielectric and nonlinear optical (NLO) switching materials.

Layered lead-halide organic-inorganic hybrid perovskites have shown great application prospects in photovoltaics and optoelectronics because of their diverse structural assemblies and richness in physical properties. In this report, a rare corrugated layer lead bromide hybrid perovskite of (demethyltropinone) 4 Pb 3 Br 10 was discovered undergoing a high-temperature reversible phase transition at 410 K, which is induced by the order-disorder transition of organic cation response to the variation of external temperature. The title compound exhibits prominent switchable dielectric behavior, coupled with semiconducting property and brilliant orange fluorescence under UV excitation. The integrated multifunction ability indicates the emergence of new promising materials and provides new fertile ground to discover more potentially useful materials.

A ferroelectric with a high phase-transition temperature (T c ) is an indispensable condition for practical applications. Over the past decades, both strain engineering and the isotope effect have been found to effectively improve the T c within ferroelectric material systems. However, the former strategy seems to prefer working in inorganic ferroelectric thin films, while the latter is also limited to some certain systems, such as hydrogen-bonded ferroelectrics. It is noted that a mono-fluorinated molecule is geometrically very similar to its parent molecule and the substitution of H by an F atom can introduce a chiral center on the molecule to template or stabilize polar structures. Significantly, the barrier of rotation of the fluorinated organic molecules is raised, resulting in a remarkable increase in T c . Herein, by applying the molecular design strategy of H/F substitution to the organic-inorganic perovskite ferroelectric (pyrrolidinium)CdCl 3 with a low T c of 240 K, two high-T c chiral perovskite ferroelectrics, (R)- and (S)-3-F-(pyrrolidinium)CdCl 3 are successfully synthesized, for which the T c reaches 303 K. The significant enhancement of 63 K in T c extends the ferroelectric working temperature range to room temperature. This finding provides a new effective way to regulate the T c in ferroelectrics and to design high-T c molecular ferroelectrics., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A novel organic-inorganic ABX3 perovskite-type material with specific hydrogen bonding interactions, N,N-dimethylethanolammonium trichlorocadmate ([DMEA]CdCl3), has been synthesized as a phase transition material. It is notable that the DMEA cations are arranged to form one-dimensional chains connected by hydrogen bonds at room temperature, which are very sparse in other perovskite-type compounds. The strong intermolecular interactions have made the phase transition temperature of the material reach up to 429 K, as confirmed by differential scanning calorimetry measurements, variable-temperature structural analyses, and dielectric measurements. The origin of the symmetry-breaking phase transition is associated with the motion or reorientation of the DMEA cations, accompanied by the crystal structures from orthorhombic Pnma to monoclinic P21/c with the temperature decreases. The finding of [DMEA]CdCl3 with unprecedented hydrogen bonding interactions has opened a new avenue to design novel phase transition materials with higher transition temperatures.

2D organic-inorganic lead iodide perovskites have recently received tremendous attention as promising light absorbers for solar cells, due to their excellent optoelectronic properties, structural tunability, and environmental stability. However, although great efforts have been made, no 2D lead iodide perovskites have been discovered as ferroelectrics, in which the ferroelectricity may improve the photovoltaic performance. Here, by incorporating homochiral cations, 2D lead iodide perovskite ferroelectrics [R-1-(4-chlorophenyl)ethylammonium] 2 PbI 4 and [S-1-(4-chlorophenyl)ethylammonium] 2 PbI 4 are successfully obtained. The vibrational circular dichroism spectra and crystal structural analysis reveal their homochirality. They both crystalize in a polar space group P1 at room temperature, and undergo a 422F1 type ferroelectric phase transition with transition temperature as high as 483 and 473.2 K, respectively, showing a multiaxial ferroelectric nature. They also possess semiconductor characteristics with a direct bandgap of 2.34 eV. Nevertheless, their racemic analogue adopts a centrosymmetric space group P2 1 /c at room temperature, exhibiting no high-temperature phase transition. The homochirality in 2D lead iodide perovskites facilitates crystallization in polar space groups. This finding indicates an effective way to design high-performance 2D lead iodide perovskite ferroelectrics with great application prospects., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

[C 6 N 2 H 18 ][SbI 5 ] (1), a novel metal halide semiconductor with dielectric relaxation behavior, has been successfully synthesized, in which the cavities between the one-dimensional [SbI 5 ] n 2- polyanions are occupied by 2-methyl-1,5-pentanediammonium (2-MPDA) cations. 1 undergoes a reversible solid-state phase transition at T C = 192.7 K and shows a step-like dielectric anomaly. Interestingly, above T C , distinct dielectric dispersion in a wide temperature range is also witnessed. Remarkably, the solid state UV-vis diffuse reflectance spectrum of 1 exhibits a slightly gentler absorption edge at about 650 nm; that is, 1 adopts an indirect band gap with 1.92 electron volts. The combined narrow band gap, strong photoconductivity effect, and excellent dielectric relaxation might shed light on the exploitation of lead-free hybrid metal halide molecular materials with promising application prospects in thermoresponsive relaxation-type dielectric materials and photovoltaic conversion devices.

Piezoelectric materials are a class of important functional materials applied in high-voltage sources, sensors, vibration reducers, actuators, motors, and so on. Herein, [(CH 3 ) 3 S] 3 [Bi 2 Br 9 ](1) is a brilliant semiconducting organic-inorganic hybrid perovskite-type non-ferroelectric piezoelectric with excellent piezoelectricity. Strikingly, the value of the piezoelectric coefficient d 33 is estimated as ≈18 pC N -1 . Such a large piezoelectric coefficient in non-ferroelectric piezoelectric has been scarcely reported and is comparable with those of typically one-composition non-ferroelectric piezoelectrics such as ZnO (3pC N -1 ) and much greater than those of most known typical materials. In addition, 1 exhibits semiconducting behavior with an optical band gap of ≈2.58 eV that is lower than the reported value of 3.37 eV for ZnO. This discovery opens a new avenue to exploit molecular non-ferroelectric piezoelectric and should stimulate further exploration of non-ferroelectric piezoelectric due to their high stability and low loss characteristics., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

For nearly 100 y, homochiral ferroelectrics were basically multicomponent simple organic amine salts and metal coordination compounds. Single-component homochiral organic ferroelectric crystals with high-Curie temperature ( T c ) phase transition were very rarely reported, although the first ferroelectric Rochelle salt discovered in 1920 is a homochiral metal coordination compound. Here, we report a pair of single-component organic enantiomorphic ferroelectrics, ( R )-3-quinuclidinol and ( S )-3-quinuclidinol, as well as the racemic mixture ( Rac )-3-quinuclidinol. The homochiral ( R )- and ( S )-3-quinuclidinol crystallize in the enantiomorphic-polar point group 6 ( C 6 ) at room temperature, showing mirror-image relationships in vibrational circular dichroism spectra and crystal structure. Both enantiomers exhibit 622 F 6-type ferroelectric phase transition with as high as 400 K [above that of BaTiO 3 ( T c = 381 K)], showing very similar ferroelectricity and related properties, including sharp step-like dielectric anomaly from 5 to 17, high saturation polarization (7 μC/cm 2 ), low coercive field (15 kV/cm), and identical ferroelectric domains. Their racemic mixture ( Rac )-3-quinuclidinol, however, adopts a centrosymmetric point group 2/ m ( C 2h ), undergoing a nonferroelectric high-temperature phase transition. This finding reveals the enormous benefits of homochirality in designing high- T c ferroelectrics, and sheds light on exploring homochiral ferroelectrics with great application., Competing Interests: The authors declare no conflict of interest.

Piezoelectric materials produce electricity when strained, making them ideal for different types of sensing applications. The most effective piezoelectric materials are ceramic solid solutions in which the piezoelectric effect is optimized at what are termed morphotropic phase boundaries (MPBs). Ceramics are not ideal for a variety of applications owing to some of their mechanical properties. We synthesized piezoelectric materials from a molecular perovskite (TMFM) x (TMCM) 1- x CdCl 3 solid solution (TMFM, trimethylfluoromethyl ammonium; TMCM, trimethylchloromethyl ammonium, 0 ≤ x ≤ 1), in which the MPB exists between monoclinic and hexagonal phases. We found a composition for which the piezoelectric coefficient d 33 is ~1540 picocoulombs per newton, comparable to high-performance piezoelectric ceramics. The material has potential applications for wearable piezoelectric devices., (Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

The past decade has witnessed much progress in designing molecular ferroelectrics, whose intrinsic mechanical flexibility, structural tunability, and easy processability are desirable for next-generation flexible and wearable electronic devices. However, an obstacle in expanding their promising applications in nonvolatile memory elements, capacitors, and sensors is effectively modulating the Curie temperature ( T c ). Here, taking advantage of fluorine substitution on the reported molecular ferroelectric, (pyrrolidinium)MnCl 3 , we present enantiomeric perovskite ferroelectrics, namely, ( R) - and ( S) -3-(fluoropyrrolidinium)MnCl 3 . The close van der Waal's radii and the similar steric parameters between H and F atoms ensure the minimum disruption of the crystal structure, while their different electronegativity and polarizability can trigger significant changes in the physical and chemical properties. As expected, the T c gets successfully increased from 295 K in (pyrrolidinium)MnCl 3 to 333 K in these two homochiral compounds. Such a dramatic enhancement of 38 K signifies an important step toward designing high- T c molecular ferroelectrics. In the light of the conceptually new idea of fluorine substitution, one could look forward to a continuous succession of new molecular ferroelectric materials and technology developments.

Quasi-spherical molecules have recently been developed as promising building blocks for constructing high-performance molecular ferroelectrics. However, although the modification of spherical molecules into quasi-spherical ones can efficiently lower the crystal symmetry, it is still a challenge to precisely arouse a low-symmetric polar crystal structure. Here, by introducing directional hydrogen-bonding interactions in the molecular modification, we successfully reduced the cubic centrosymmetric Pm3̅ m space group of [quinuclidinium]ClO 4 at room temperature to the orthorhombic polar Pna2 1 space group of [3-oxoquinuclidinium]ClO 4 . Different from the substituent groups of -OH, -CH 3 , and ═CH 2 , the addition of a ═O group with H-acceptor to [quinuclidinium] + forms directionally N-H···O═C hydrogen-bonded chains, which plays a critical role in the generation of polar structure in [3-oxoquinuclidinium]ClO 4 . Systematic characterization indicates that [3-oxoquinuclidinium]ClO 4 is an excellent molecular ferroelectric with a high Curie temperature of 457 K, a large saturate polarization of 6.7 μC/cm 2 , and a multiaxial feature of 6 equiv ferroelectric axes. This work demonstrates that the strategy of combining quasi-spherical molecule building blocks with directional intermolecular interactions provides an efficient route to precisely design new eminent molecular ferroelectrics.

The perovskite structure is rich in ferroelectricity. In contrast, ferroelectric antiperovskites have been scarcely confirmed experimentally since the discovery of M 3 AB-type antiperovskites in the 1930s. Ferroelectricity is now revealed in an organic-inorganic hybrid X 3 AB antiperovskite structure, which exhibits a clear ferroelectric phase transition 6/mmmF6mm with a high Curie point of 480 K. The physical properties across the phase transition are obviously changed along with the symmetry requirements, providing solid experimental evidence for the ferroelectric phase transition. More interestingly, the discovered antiperovskite shows intense photoluminescence and triboluminescence properties. The confirmation of the triboluminescent ferroelectric antiperovskite will open new avenues to explore excellent optoelectronic properties in the antiperovskite family., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The rational selection of ligands is vitally important in the construction of new organic-inorganic hybrid three-dimensional perovskite complexes. As part of an exploration of perovskite-type materials, two new Na-I compounds based on the piperazine ligand, namely poly[piperazinediium [tri-μ-iodido-sodium]], {(C 4 H 12 N 2 )[NaI 3 ]} n , 1, and catena-poly[tris(piperazinediium) [[triiodidosodium]-μ-iodido] triiodide monohydrate], {(C 4 H 12 N 2 ) 3 [NaI 4 ]I 3 ·H 2 O} n , 2, have been synthesized by adjusting the stoichiometric ratio of sodium iodide and piperazine, and were characterized by single-crystal X-ray diffraction. In the crystal structures of 1 and 2, each Na I cation is linked to six I atoms, but the compounds show completely different configurations. In 1, the structure includes a perovskite-like array of vertex-sharing NaI 6 octahedra stretching along the direction of the three axes, and each piperazinediium dication is enclosed in the NaI 3 perovskite cage. However, in 2, each Na I atom bridges a single I atom to form a one-dimensional linear chain, and complex intermolecular hydrogen bonds connect these one-dimensional chains into a three-dimensional supramolecular network., (open access.)

Two isostructural ionic cobalt(ii) halides, trimethylchloromethyl ammonium tetrachlorocobalt(ii) (1, [Me3NCH2Cl]2[CoCl4]) and trimethylbromomethyl ammonium tetrabromocobalt(ii) (2, [Me3NCH2Br]2[CoBr4]), have been discovered as new high-temperature phase transition materials. 1 exhibits two successive structural phase transitions from P212121 to P21/c at 252 K and then to Pnma at 335 K, accompanied by step-like dielectric anomalies. The two-step sequential reversible phase transitions of 1 derive from the order-disorder transformation of CoCl4 anions and organic Me3NCH2Cl cations, respectively. Its analogue 2 also crystallizes in P21/c at 293 K by changing the halogen atoms of both cations and anions of 1. Unlike 1, 2 displays only one structural phase transition with a much higher transition temperature at 387 K, which is mainly influenced by intermolecular interactions and more energy is required to provide the freedom of the motion. All the findings in the present work indicate that the phase transition temperature and properties of materials can be tuned by using halogens in this series of compounds, which could open a new way to design and assemble novel high-temperature phase transition materials.

With the flourishing development of (CH 3 NH 3 )PbI 3 , three-dimensional (3D) organic-inorganic perovskites with unique structure-property flexibility have become a worldwide focus. However, they still face great challenges in effectively inducing ferroelectricity. Despite the typical 3D perovskite structure and the ability of dabco (1,4-diazabicyclo[2.2.2]octane) to trigger phase transition, unfortunately [H 2 dabco]RbCl 3 adopts a nonpolar crystal structure without ferroelectricity. Within the larger RbI 3 framework, we assemble N-methyl-1,4-diazoniabicyclo[2.2.2]octane (MeHdabco) obtained by reducing the molecular symmetry of dabco into a new 3D organic-inorganic perovskite. As expected, MeHdabco bearing a molecular dipole moment turns out to be vital in the generation of polar crystal structure and ferroelectric phase transition occurring at 430 K. It is the first time that the dabco component has been successfully wrapped into a 3D cage to achieve ferroelectricity even through there is intensive research on dabco. This precise molecular design strategy based on the modification of molecular symmetry provides an efficient route to enrich the family of 3D organic-inorganic perovskite ferroelectrics. Intriguingly, the iodine-doped crystal can exhibit intense saffron yellow luminescence with a high quantum yield of 17.17% under UV excitation, extending its application in the field of ferroelectric luminescence and/or multifunctional devices.

Two hybrids (C 5 H 6 N)CdCl 3 (1) and (C 5 H 6 N)Cd 2 Cl 5 (2) were synthesized by stoichiometric regulation of reactants. 1 with a one-dimensional chain-like structure shows a step-like dielectric anomaly at around 158 K. 2 with a layered structure undergoes a prominent phase transition in the vicinity of 182 K, accompanying obvious dielectric relaxation behavior in a broad temperature range. Systematic characterization, such as differential scanning calorimetry (DSC), single-crystal X-ray diffraction, and dielectric measurements, has demonstrated that the phase transitions of 1 and 2 are both attributable to the dynamic motion of the organic cation. Significantly, dimensionality modulation triggers the tunable dielectric responses in these two compounds. Thus, regulation of the phase transition temperature and dielectric responses in the various dimensions of the structure is a potentially effective method to construct tunable dielectric phase transition materials.

The process of molecular recognition is the assembly of two or more molecules through weak interactions. Information in the process of molecular recognition can be transmitted to us via physical signals, which may find applications in sensing and switching. The conventional signals are mainly limited to light signal. Here, we describe the recognition of diols with Cu(1,10-phenlothroline) 2 SeO 4 and the transduction of discrete recognition events into dielectric and/or ferroelectric signals. We observe that systems of Cu(1,10-phenlothroline) 2 SeO 4 ·(diol) exhibit significant dielectric and/or ferroelectric dependence on different diol molecules. The compounds including ethane-1,2-diol or propane-1,2-diol just show small temperature-dependent dielectric anomalies and no reversible polarization, while the compound including ethane-1,3-diol shows giant temperature-dependent dielectric anomalies as well as ferroelectric reversible spontaneous polarization. This finding shows that dielectricity and/or ferroelectricity has the potential to be used for signalling molecular recognition.

Two new manganese(II) based organic-inorganic hybrid compounds, C11H21Cl3MnN2 (1) and C11H22Cl4MnN2 (2), with prominent photoluminescence and dielectric properties were synthesized by solvent modulation. Compound 1 with novel trigonal bipyramidal geometry exhibits bright red luminescence with a lifetime of 2.47 ms and high quantum yield of 35.8 %. Compound 2 with tetrahedral geometry displays intense long-lived (1.54 ms) green light emission with higher quantum yield of 92.3 %, accompanied by reversible solid-state phase transition at 170 K and a distinct switchable dielectric property. The better performance of 2 results from the structure, including a discrete organic cation moiety and inorganic metal anion framework, which gives the cations large freedom of motion., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A new organic-inorganic hexagonal perovskite-type compound with the formula ABX3, thiazolium tribromocadmate(ii) (1), in which thiazolium cations are situated in the space between the one-dimensional chains of face-sharing CdBr(6) octahedra, has been successfully synthesized. Systematic characterizations including differential scanning calorimetry measurements, variable-temperature structural analyses, and dielectric measurements reveal that it undergoes two structural phase transitions, at 180 and 146 K. These phase transitions are accompanied by remarkable dielectric relaxation and anisotropy. The thiazolium cations remain orientationally disordered during the two phase transition processes. The origins of the phase transitions at 180 and 146 K are ascribed to the slowing down and reorientation of the molecular motions of the cations, respectively. Moreover, the dielectric relaxation process well described by the Cole-Cole equation and the prominent dielectric anisotropy are also connected with the dynamics of the dipolar thiazolium cations.

Objective: To evaluate left ventricular function in newborn infants of mothers with gestational diabetes mellitus (GDM)., Methods: Forty newborn infants of mother with GDM (GDM group) and forty normal newborn infants (control group) were enrolled in this study. Two-dimensional speckle tracking imaging was used to measure interventricular septal thickness, posterior left ventricular wall thickness and left ventricular ejection fraction in both groups. Left ventricular rotation and torsion were evaluated for all participants., Results: Interventricular septal thickness in the GDM group was much higher than in the control group (0.45±0.06 mm vs 0.34±0.05 mm; P<0.05). Posterior left ventricular wall thickness in the GDM group was also higher than in the control group (0.45±0.17 mm vs 0.31±0.02 mm; P<0.05). There was no difference in the left ventricular ejection fraction between the two groups (P>0.05). Peak subendocardial rotation, peak subepicardial rotation, peak bulk rotation and peak mural torsion were higher in the GDM group than in the control group (P<0.05)., Conclusions: Cardiac function may be impaired in newborn infants of mothers with GDM, with changes in left ventricular shape and abnormalities of left ventricular rotation and torsion. However, infants have a normal ventricular blood ejection under the cardiac compensation. Two-dimensional speckle tracking imaging technique can be used for early detection of left ventricular function.