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Organic ferroelectrics have received a great deal of interest due to their exclusive properties. However, organic ferroelectrics have not been fully explored, which hinders their practical application. Here, we presented a novel metal‐free organic molecular ferroelectric [4‐MCHA][ClO4] (1) (4‐MCHA=trans‐4‐methylcyclohexylamine), which exhibits an above‐room‐temperature of 328 K. Strikingly, the single crystal structure analysis of 1 shows that the driving force of phase transition is related to the interesting chair‐boat conformation change of 4‐MCHA cation, in addition to the order‐disorder transition of ClO4− anion. Using piezoelectric response force microscopy (PFM), the presence of domains and the implemented polarization switching were clearly observed, which explicitly determined the presence of room‐temperature ferroelectricity of 1. As far as we know, the ferroelectric phase transition mechanism attributed to the conformational change in a trans isomeric cation is very rare. This research enriched the path of designing ferroelectric materials and smart materials. [ABSTRACT FROM AUTHOR]

Although organic molecule phase transition materials (OMPTM) have been studied by many scholars owing to their light weight and easy processing, single-component OMPTM with two reversible phase transitions have rarely been reported. Herein, we report an organic inner salt, 1-sulfo-4-dimethylamino-pyridinium (1), which exhibits two phase transitions at 286 K and 311 K, accompanied by obvious dielectric anomalies. Moreover, the variable-temperature single X-ray crystal structure analysis revealed that 1 undergoes an order–disorder symmetry breaking from 243 K (phase I) to 293 K (phase II), in which the centrosymmetric space group P21/n is transformed into the space group of Pnma. However, from phase II to phase III, there is no space group change, and 1 proceeds with an isostructural phase transition. Overall, this study highlights the exploration of the phase transition mechanism of single-component OMPTM. [ABSTRACT FROM AUTHOR]

The emergence of (CH3NH3)PbI3 has brought the development of three‐dimensional (3D) organic‐inorganic hybrid perovskite (OIHP) structures with ABX3 type to a higher level; however, most 3D frameworks are constructed by corner‐sharing of BX6 octahedra. Herein, we substituted the spherical molecule 1,4‐diazabicyclo[2.2.2]octane (2.2.2‐dabco) with 1,4‐diazabicyclo[3.2.2]nonane (1,4‐3.2.2‐dabcn) as a template to react with RbX (X=Br, I) in the corresponding HX acids under the consideration of reducing the molecular symmetry. Two 3D OIHP compounds [1,4‐3.2.2‐H2dabcn]RbI3⋅H2O (1) and [1,4‐3.2.2‐H2dabcn]RbBr3 (2) crystallized in non‐centrosymmetric point group mm2 before the phase transition point were isolated. Among them, the 3D inorganic framework of 1 is constructed by sharing the corner of [RbI6] octahedra, while that of 2 is constructed by sharing the corner and face of [RbBr6] octahedra to acquire large cavities to accommodate the organic amine cation [1,4‐3.2.2‐H2dabcn]2+; this 3D framework type is unprecedented in the OIHPs. As expected, compounds 1 and 2 exhibit reversible phase transition, dielectric and second harmonic generation (SHG) and ferroelectric properties, in which the phase transition temperature of 2 at 374 K is much higher than compound 1 at 280 K. [ABSTRACT FROM AUTHOR]

Organic–inorganic hybrid perovskites are categorized as multifunctional materials due to their structural designability and functional diversity. Herein, two manganese-based organic–inorganic perovskite type compounds [Me3NNH2]MnCl3 (1) and [(CH3)3NCH2CH2F]2MnCl4 (2) were synthesized by reactions of trimethylhydrazine iodide and (fluoromethyl)trimethylammonium bromide with MnCl2 in concentrated hydrochloric acid aqueous solution. Differential scanning calorimetry (DSC) and dielectric measurements revealed that compounds 1 and 2 undergo reversible phase transitions at about 327 K and 352 K, respectively. Significantly, under the excitation of 365 nm, compounds 1 and 2 emit green and red luminescence, which originate from the octahedral [MnCl6] and tetrahedral [MnCl4] moieties. [ABSTRACT FROM AUTHOR]

The excellent properties of host–guest crown ether inclusions in phase transition, dielectric and second-order nonlinear optical properties have attracted much attention. In this paper, we successfully designed and prepared two novel host–guest crown ether supramolecules [(DFBA)(15-crown-5)]X (X = ClO4−, 1; ReO4−, 2) by reactions of 2,6-difluorobenzylamine (DFBA) with 1,4,10,13-pentaoxacyclopentadecane (15-crown-5) in HClO4, or HReO4 aqueous solution. By the introduction of difluoro-substituted benzylamine as a guest cation, the phase transition temperatures are greatly increased to 377 K for 1 and 391 K for 2. More importantly, the space group of 1 has changed from centrosymmetric (CS) P2/c to the non-centrosymmetric (NCS) Pca21 in 2 when substituting perchlorate (ClO4−) with the larger and heavier perrhenate (ReO4−), which leads to 2 showing a switchable and stable second-harmonic generation (SHG) effect. According to the principle of momentum matching between a cation and anion, the perrhenate group increases the energy barrier of the molecular thermal motion, which not only significantly increases the phase transition temperature of 2 but also causes it to be frozen and crystallized in a NCS space group at room temperature. This research demonstrates that a polar molecule can adjust the suitability of anions and cations inside the crystal by practical chemical means. [ABSTRACT FROM AUTHOR]

Often, the quasi-spherical molecule 1,4-diazabicyclo[2.2.2]octane (2.2.2-dabco) is chosen to prepare switchable materials with a high phase transition temperature. We wished to reduce molecular symmetry but maintain a quasi-spherical shape. Hence, a similar molecule, 1,4-diazabicyclo[3.2.2]nonane (3.2.2-dabcn), was used to react with equimolar amounts of HClO4 or HReO4 in aqueous solution. Two compounds [3.2.2-Hdabcn]X (X = ClO4, 1; ReO4, 2) with high phase-transition points at 418 K for 1 and 394.6 K and 419.2 K for 2, respectively, were isolated, in which one-dimensional cationic chains were connected by different types of hydrogen bonds. Differential scanning calorimetry and dielectric-permittivity measurements revealed that 1 and 2 showed switchable phase transition and dielectric anomalies. Compound 1 also showed a reversible second-harmonic-generation effect. [ABSTRACT FROM AUTHOR]

Recently, hybrid organic‐inorganic lead halide materials have attracted great attention for their applications in the fields of light‐emitting diodes, photovoltaics, photodetector. However, these hybrid materials usually suffer from environmental and human health issues because of the toxic lead moieties. Herein, we report a novel lead‐free bismuth iodide phase transition material, [NH3(CH2)7NH3][BiI5] (1), which undergoes a reversible phase transition at high temperature 351.7 K and exhibits a step fashion dielectric anomaly. The structural phase transition of 1 is mainly originated from the order‐disorder transition of the 1,7‐heptanediamine cations. Besides, the solid‐state UV‐vis spectrum of 1 displays an intense adsorption at around 658 nm; which gives an indirect bandgap of 1.89 eV. Such a small bandgap value is comparable to most of the organic‐inorganic hybrid lead halide type semiconductors. We believe this study will shed light on the exploration of lead‐free organic‐inorganic hybrid metal halide semiconductors toward future device applications. [ABSTRACT FROM AUTHOR]

A one-dimensional organic–inorganic hybrid perovskite material [3.3.0-dabco]PbBr3 (1) was synthesized by the reaction of 1,5-diazabicyclo[3.3.0]octane (3.3.0-dabco) with PbBr2 in concentrated HBr aqueous solution. Differential scanning calorimetry, dielectric measurements, and variable-temperature structural analyses revealed that compound 1 exhibits two successive structural phase transitions from P212121 to Pbcm at 387 K (T1) and then to P6/mmc at 436 K (T2), accompanied by two pairs of dielectric anomalies with a clear one at T1 and an unobvious one at T2. In addition, compound 1 shows a robust second harmonic generation (SHG) effect between SHG-OFF and SHG-ON states during its centrosymmetric to non-centrosymmetric symmetry breaking phase transition at T1. [ABSTRACT FROM AUTHOR]

Recently, the development of multifunctional thermochromic materials that exhibit switching characteristics in phase transition and dielectric properties has attracted widespread attention due to their potential application in signal processing and smart devices. But most traditional thermochromic materials tend to be rather than reversible phase change materials. Here, a square-pyramidal coordinated copper complex [Me3NNH2CuCl3]2 (1) (Me3NNH2 = trimethyl hydrazine) showing switchable properties in phase transition, dielectricity and thermochromic properties has been prepared by reaction of Me3NNH2I with CuCl2 in concentrated HCl aqueous solution. Compound 1 has a reversible phase transition temperature of 45 °C. When the temperature exceeds the phase transition temperature, the green color of 1 gradually changed into dark red. Compared with traditional thermochromic materials, the reversible phase transition and dielectric properties within the thermochromic materials will bring additional spectral encryption possibilities for future information processing. [ABSTRACT FROM AUTHOR]

Abstract: The perovskite structure is rich in ferroelectricity. In contrast, ferroelectric antiperovskites have been scarcely confirmed experimentally since the discovery of M3AB‐type antiperovskites in the 1930s. Ferroelectricity is now revealed in an organic–inorganic hybrid X3AB 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. [ABSTRACT FROM AUTHOR]

An octahedral coordinated nickel(II) hydrazinium complex was prepared by reaction of NiCl 2 with trimethyl hydrazinium showing reversible phase transition, dielectric anomaly and thermochromism. [Display omitted] • A nickel complex based on hydrazinium exhibits switchable thermochromic properties. • The nickel complex also shows reversible dielectric property and phase change. • The mechanism of thermochromism was explained by single crystal X-ray diffraction. Thermochromism in copper complexes is known, but nickel thermochromic complex materials are less reported. Herein, we synthesized a nickel metal complex [(Me 3 NNH 2) 2 NiCl 4 ] (1) based on 1,1,1-trimethylhydrazinium iodide and nickel chloride, which exhibited excellent switching properties in terms of dielectric and phase change and thermochromic properties from yellow to blue. Compound 1 was subjected to the variable temperature single crystal X-ray diffraction, and it was found that the crystal space group did not change after the temperature exceeded the phase transition point, so the thermochromism may be caused by the structural phase transition of the compound. [ABSTRACT FROM AUTHOR]

• Synthesis two lead-free halides [3-FPEA] 3 (SbCl 4)Cl 2 and [3-FPEA] 4 (BiI 6)I. • Both hybrid perovskites have reversible phase transitions. • Both materials are lead-free semiconductor materials. Metal halide organic-inorganic hybrid perovskite is a kind of rapid development of semiconductors but its major development has been concentrated in lead-based perovskites. Here we report two zero-dimensional non-lead halide perovskites [3-FPEA] 3 (SbCl 4)Cl 2 (1) and [3-FPEA] 4 (BiI 6)I (2) (3-FPEA = 3-fluorophenethylamine) with the reversible phase transitions. The differential scanning calorimetry (DSC) and UV-vis absorption measurements of 1 and 2 revealed that the phase transition temperatures are 350 K (1) and 335 K (2), the bandgaps are 3.53 eV (1) and 2.14 eV (2), respectively. The room temperature X-ray single crystal diffraction showed the cation [3-FPEA]+ in 1 and 2 proceeds a twofold disorder, and the anions in 1 are a dimer [Sb 2 Cl 10 ] constructed with [SbCl 6 ] octahedra by sharing the Cl···Cl edge, and the anions in 2 are the discrete [BiI 6 ] octahedron. This study can provide an effective molecular design strategy for exploring and investigating non-lead-based halide perovskite semiconductive phase change materials. [Display omitted] [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) organic-inorganic hybrid perovskite (OIHP) has the advantages of excellent material stability, structural diversity and ease of manufacturability. It is worth noting that the fluorination strategy has been recognized as a convenient molecular design method that can effectively customize and optimize physical and chemical properties in 2D OIHP materials. However, selection the fluorine-chlorine double substituted organic amine to construct lead halide OIHP molecules was not reported. Here, for the first time, we successfully obtained a 2D metal halide perovskite compound [4-Cl-2-FBA] 2 PbBr 4 (1) by reactions of lead bromide with two equivalents of 4-chloro-2-fluorobenzylamine [4-Cl-2-FBA] in concentrated HBr aqueous solution. Its crystal structure and purity were confirmed by X-ray single crystal diffraction and powder X-ray diffraction (PXRD). Differential scanning calorimetry (DSC) and dielectric measurement analyses showed the phase transition (PT) temperature of 1 is 380.1 ​K which is higher than that of [2-FBA] 2 PbBr 4 , (2-FBA ​= ​2-fluorobenzylammonium, 364 ​K), but lower than those of (benzylammonium) 2 PbBr 4 (405 ​K) and [PFBA] 2 PbBr 4 (PFBA ​= ​perfluorobenzylammonium, 440 ​K). A two-dimensional (2D) organic-inorganic hybrid perovskite material [4-Cl-2-FBA] 2 PbBr 4 (1) with high phase transition temperature and semiconductive property was isolated by reactions of lead bromide with two equivalents of 4-chloro-2-fluorobenzylamine [4-Cl-2-FBA] in concentrated HBr aqueous solution. [Display omitted] • A fluorine and chlorine substituted 2D metal halide perovskite was firstly prepared by reactions of PbBr 2 ​with 4-chloro-2-fluorobenzylamine. • DSC analysis showed the phase transition temperature of ​ 1 ​is 380.1 K which is higher than that of [2-FBA] 2 PbBr 4 ​at 364 K. • The 2D metal halide perovskite was characterized by the variable temperature X-ray single crystal diffraction. [ABSTRACT FROM AUTHOR]