High‐ Tc Enantiomeric Ferroelectrics Based on Homochiral Dabco‐derivatives (Dabco=1,4‐Diazabicyclo[2.2.2]octane)

Shape Shifting and Locking in Mechanically Responsive Organic-Inorganic Hybrid Materials for Thermoelastic Actuators

The construction of mechanically responsive materials with reversible shape-shifting, shape-locking, and stretchability holds promise for a wide range of applications in fields such as soft robotics and flexible electronics. Here, we report novel thermoelastic one-dimensional organic-inorganic hybrids (R/S-Hmpy)PbI3 (Hmpy=2-hydroxymethyl-pyrrolidinium) to show mechanical responses. The single crystals undergo two phase transitions at 310 K and 380 K. When heated to 380 K, they show shape-shifting and expansion along the b-axis by about 13.4 %, corresponding to a larger deformation than that of thermally activated shape memory alloys (8.5 %), and exhibit a strong actuation force. During the cooling process, the stretched crystal shape maintains and a shape-locking phenomenon occurs, which is lifted when the temperature decreases to 305 K. Meanwhile, due to the introduction of chiral ions, the thermal switching shows a 10-fold second-order nonlinear switching contrast (common values typically below 3-fold). This study presents a thermoelastic actuator based on shape-shifting and -locking of organic-inorganic hybrids for the first time. The dielectric and nonlinear optical switching properties of organic-inorganic hybrids broaden the range of applications of mechanically responsive crystals.

The First Discovery of Spherical Carborane Molecular Ferroelectric Crystals

Carborane compounds, known for their exceptional thermal stability and non-toxic attributes, have garnered widespread utility in medicine, supramolecular design, coordination/organometallic chemistry, and others. Although there is considerable interest among chemists, the integration of suitable carborane molecules into ferroelectric materials remains a formidable challenge. In this study, we employ the quasi-spherical design strategy to introduce functional groups at the boron vertices of the o-carborane cage, aiming to reduce molecular symmetry. This approach led to the successful synthesis of the pioneering ferroelectric crystals composed of cage-like carboranes: 9-OH-o-carborane (1) and 9-SH-o-carborane (2), which undergo above-room ferroelectric phase transitions (Tc) at approximately 367 K and 347 K. Interestingly, 1 and 2 represent uniaxial and multiaxial ferroelectrics respectively, with 2 exhibiting six polar axes and as many as twelve equivalent polarization directions. As the pioneering instance of carborane ferroelectric crystals, this study introduces a novel structural archetype for molecular ferroelectrics, thereby providing fresh insights into the exploration of molecular ferroelectric crystals with promising applications.

The past 10 years of molecular ferroelectrics: structures, design, and properties

Ferroelectricity, which has diverse important applications such as memory elements, capacitors, and sensors, was first discovered in a molecular compound, Rochelle salt, in 1920 by Valasek. Owing to their superiorities of lightweight, biocompatibility, structural tunability, mechanical flexibility, etc., the past decade has witnessed the renaissance of molecular ferroelectrics as promising complementary materials to commercial inorganic ferroelectrics. Thus, on the 100th anniversary of ferroelectricity, it is an opportune time to look into the future, specifically into how to push the boundaries of material design in molecular ferroelectric systems and finally overcome the hurdles to their commercialization. Herein, we present a comprehensive and accessible review of the appealing development of molecular ferroelectrics over the past 10 years, with an emphasis on their structural diversity, chemical design, exceptional properties, and potential applications. We believe that it will inspire intense, combined research efforts to enrich the family of high-performance molecular ferroelectrics and attract widespread interest from physicists and chemists to better understand the structure-function relationships governing improved applied functional device engineering.

Exploring the potential applications of lead-free organic-inorganic perovskite type [NH3(CH2)nNH3]MCl4 (n = 2, 3, 4, 5, and 6; M = Mn, Co, Cu, Zn, and Cd) crystals

The organic-inorganic hybrid perovskite compounds have been extensively studied since the dawn of a new era in the field of photovoltaic applications. Up to now, perovskites have proven to be the most promising in terms of power conversion efficiency; however, their main disadvantages for use in solar cells are toxicity and chemical instability. Therefore, it is essential to develop a hybrid perovskite that can be replaced with lead-free materials. This review focuses on the possibility of applying lead-free organic-inorganic perovskite types [NH3(CH2)nNH3]MCl4 (n = 2, 3, 4, 5, and 6; M = Mn, Co, Cu, Zn, and Cd) crystals. We are seeking organic-inorganic hybrid perovskite materials with very high temperature stability or without phase transition temperature, and thermal stability. Thus, by considering the characteristics according to the methylene lengths and the various transition metals, we aim to identify improved materials meeting the criteria mentioned above. Consequently, the physicochemical properties of organic-inorganic hybrid perovskite [NH3(CH2)nNH3]MCl4 regarding the effects of various transition metal ions of the anion and the methylene lengths of the cation are expected to promote the development and application of lead-free hybrid perovskite solar cells.

A Sn-Based Hybrid Ferroelastic Semiconductor with High-Temperature Dielectric Switching

Organic-inorganic halide hybrids have been extensively developed and used in optoelectronic devices because of their superior performance such as ease of assembly, flexible structural tunability, and excellent optoelectronic properties. Ferroelastic strain might be used to modulate and control photoelectric properties such as photovoltaic voltage, while organic-inorganic hybrid ferroelastic semiconductors remain relatively unexplored. Herein, we successfully design a new Sn-base, lead-free hybrid ferroelastic semiconductor, [TPMA]2[SnCl6] (TPMA = benzyl trimethylammonium). It undergoes a high-temperature -3mF-1-type ferroelastic phase transition at 408 K, and intriguingly, its ferroelastic domains can be simultaneously switched under the stimulation of external heat and stress. The ferroelastic phase transition might be derived from the order-disorder transition of organic cations during heating and cooling. Moreover, [TPMA]2[SnCl6] also demonstrates a high-temperature dielectric switching property around 408 K, which has good stability and reproducibility. With those benefits, [TPMA]2[SnCl6] shows great potential in applications such as energy storage devices, optoelectronic devices, shape memory, intelligent switches, and so on.

The halogen substitution strategy of inorganic skeletons triggers dielectric and band gap regulation of hybrid perovskites

Organic-inorganic hybrid perovskites (OIHPs) with dielectric switching functions have aroused comprehensive scientific interest, benefitting from their promising applications in sensors and information storage. However, to date, most of these materials discovered thus far possess a single function and are limited in their applicability, failing to meet the requirements of diverse applications. Moreover, the discovery of these materials has been largely serendipitous. Building multifunctional OIHPs with dielectric switching and semiconductors remains a daunting task. In this context, by introducing [C7H16N]+ as cations and in combination with lead halide with semiconducting properties, two OIHPs [C7H16N]PbI3 (1) and [C7H16N]PbBr3 (2) ([C7H16N]+ = (cyclopropylmethyl) trimethylammonium) have been successfully designed. They have dielectric switching properties close to 253 and 279 K and semiconducting behavior with band gaps of 2.67 and 3.22 eV. The phase transition temperature increased by 26 K through halogen substitution. In summary, our findings in this study provide insights into the application of the halogen substitution regulation strategy and open up new possibilities for designing perovskite semiconductors with dielectric switching functionality.

Processing on crystal growth, structure, thermal property, and nuclear magnetic resonance of organic-inorganic hybrid perovskite type [NH3(CH2)6NH3]ZnCl4 crystal

Organic-inorganic hybrid compounds have recently gained significant attention in recent years due to their diverse applications. Herein, [NH3(CH2)6NH3]ZnCl4 crystals were grown, and their triclinic structure, phase transition temperature (TC = 408 K), and high thermal stability (Td = 584 K) was determined using X-ray diffraction (XRD), differential scanning calorimetry, and thermogravimetry measurements. By analyzing the chemical in response to temperature changes, we observed that the coordination geometry around 1H and 13C were highly symmetric below TC, whereas their symmetry was lowered above TC. The change of N-H⋯Cl hydrogen bond from XRD results and the change of 14N NMR chemical shifts was due to the changes to the coordination geometry of Cl- around Zn2+ in the ZnCl4 anion. The activation energy of 1H was three times greater than that of 13C, and this result indicates that the energy transfer of 13C was easier than those of 1H. We compared the results for [NH3(CH2)nNH3]ZnCl4 (n = 6) studied here with those for n = 2, 3, 4, and 5 obtained from previous studies. The characteristics of the length of CH2 in the methylene chain are expected to be used for potential applications in the near future.

Zero-Dimensional Sn-Based Enantiomeric Phase-Transition Materials with High-Tc and Dielectric Switching

The combination of chirality and phase-transition materials has broad application prospects. Therefore, based on the quasi-spherical theory and the thought strategy of introducing chirality, we have successfully synthesized a pair of chiral enantiomeric ligands (R/S)-triethyl-(2-hydroxypropyl)ammonium iodide, which can be combined with a tin hexachloride anion to obtain a pair of new organic-inorganic hybrid enantiomeric high-temperature plastic phase-transition materials: (R/S)-[CH3 CH(OH)CH2 N(CH2 CH3 )3 ]2 SnCl6 (1-R/1-S), which have a high temperature phase transition of Tc =384 K, crystallize in the P21 chiral space group at room temperature, and have obvious CD signals. In addition, compounds 1-R and 1-S have a good low-loss dielectric switch and broadband gap. This work is conducive to the research into chiral high-temperature reversible plastic phase-transition materials, and promotes the development of multi-functional phase-transition materials.

Targeted regulation and optimization of multifunctional phase transition materials by novel void occupancy engineering

As an innovative form of stimulus-response materials, organic-inorganic hybrid phase transition materials have become a wonderful contender in the field of functional electronic equipment due to their versatile structure, intensive functions and straightforward preparation. However, the targeted regulation and optimization of the electrical/optical response, along with the establishment of regular structure-performance relationships, pose significant challenges in meeting the diverse demands of practical applications over an extended period. Herein, we conducted a systematic investigation into the role of lattice void occupancy in regulating phase transition temperature (Tp) and related optical/electrical bistability. By taking hybrid material [TMEA][Cd(SCN)3] featuring a flexible ammonium cation [TMEA]+ (TMEA = ethyltrimethylammonium) as the prototype, we successfully synthesized three phase transition materials, namely [DEDMA][Cd(SCN)3], [TEMA][Cd(SCN)3] and [TEA][Cd(SCN)3] (DEDMA = diethyldimethylammonium, TEMA = triethylmethylammonium, and TEA = tetraethylammonium), and the excellent regulation of the physical properties of these compounds was achieved through subtle engineering of void occupancy. More strikingly, [TEA][Cd(SCN)3] exhibits remarkable bistable properties in terms of dielectric and nonlinear optical responses (with second-harmonic generation intensity reaching 2.5 times that of KDP). This work provides a feasible avenue to reasonably customise organic-inorganic hybrid phase transition materials and finely adjust their intriguing functionalities.

The First Enantiomeric Stereogenic Sulfur-Chiral Organic Ferroelectric Crystals

Chiral ferroelectric crystals with intriguing features have attracted great interest and many with point or axial chirality based on the stereocarbon have been successively developed in recent years. However, ferroelectric crystals with stereogenic heteroatomic chirality have never been documented so far. Here, we discover and report a pair of enantiomeric stereogenic sulfur-chiral single-component organic ferroelectric crystals, Rs -tert-butanesulfinamide (Rs -tBuSA) and Ss -tert-butanesulfinamide (Ss -tBuSA) through the deep understanding of the chemical design of molecular ferroelectric crystals. Both enantiomers adopt chiral-polar point group 2 (C2 ) and exhibit mirror-image relationships. They undergo high-temperature 432F2-type plastic ferroelectric phase transition around 348 K. The ferroelectricity has been well confirmed by ferroelectric hysteresis loops and domains. Polarized light microscopy records the evolution of the ferroelastic domains, according with the fact that the 432F2-type phase transition is both ferroelectric and ferroelastic. The very soft characteristics with low elastic modulus and hardness reveals their excellent mechanical flexibility. This finding indicates the first stereosulfur chiral molecular ferroelectric crystals, opening up new fertile ground for exploring molecular ferroelectric crystals with great application prospects.

Investigation of the structure, phase transitions, molecular dynamics, and ferroelasticity of organic-inorganic hybrid NH(CH3)3CdCl3 crystals

Understanding the physical and chemical properties of the organic-inorganic hybrid NH(CH₃)₃CdCl₃ is essential for its application. Considering its importance, a single crystal of NH(CH₃)₃CdCl₃ was grown with an orthorhombic structure at 300 K. The phase transition temperatures were determined to be 345 (T_C3), 376 (T_C2), and 452 K (T_C1) (phases IV, III, II, and I, respectively, starting from a low temperature). The partial decomposition temperature was 522 K (T_d). Furthermore, the NMR chemical shifts of the ¹H, ¹³C, and ¹¹³Cd atoms of the cation and anion varied with increasing temperature. Consequently, a significant change in the coordination geometry of Cl around Cd in CdCl₆ and a change in the coordination geometry of H in NH was associated with changes in the N-H⋯Cl hydrogen bond near the phase transition temperature. The ¹³C activation energy E_a obtained from the spin-lattice relaxation time was smaller than that of ¹H E_a, suggesting that energy transfer around ¹³C is easier. Additionally, a comparison of the twin domain walls measured via optical polarizing microscopy and Sapriel's theory indicated that the crystal structure in phase III was more likely to be orthorhombic than hexagonal.

Fluorescence Emission Is Highly Structure-Dependent in Hybrid Lead Halides

Hybrid lead halide perovskites have received extensive scientific attention owing to their great potential in the field of fluorescent displays and light-emitting diodes. Currently, most luminescent materials contain functional molecular and rare-earth metal ion parts. However, the mechanism of photoluminescence property in two-dimensional hybrid lead halide perovskites with different layered inorganic skeletons has been reported rarely. To better understand the effect of an inorganic skeleton on the fluorescence property, here, we report three organic-inorganic hybrid materials with different layered inorganic frameworks: (MACH)₂·PbBr₄ (Prv-1, MACH = cyclohexylmethylammonium), (2-MPQ)·PbBr₄ (Prv-2, 2-MPQ = 2-methylpiperazinium), and (TMBA)₄·Pb₃Br₁₀ (Prv-3, TMBA = N'N'N'-trimethylbenzylammonium). Among them, Prv-1 is a (100)-oriented perovskite, Prv-2 belongs to the (110)-oriented perovskite, and the inorganic framework of Prv-3 possesses [Pb₃Br₁₀] units. Interestingly, Prv-1 has a strong blue-violet fluorescence emission, while the luminescence effect of Prv-2 is very weak; notably, Prv-3 emits a charming bright-orange light. Meanwhile, results of theoretical computational studies also reveal that the electronic structure of all three compounds is highly dependent on structurally distorted [PbBr₆] octahedra, and the frontier molecular orbital (FMO) analysis further suggests that HOMO and LUMO of Prv-3 are contributed by inorganic and organic components, respectively. In addition, all three materials belong to direct band gap semiconductors, and the band gaps are 2.79, 2.97, and 2.76 eV, respectively. Significantly, there are obvious differences in conduction bands. Based on the above analysis, the photoluminescence mechanism of three hybrid materials is explained from the electronic levels. Consequentially, this work might provide practical strategies and perspectives for exploring novel structure-related properties.

Inversion of Molecular Chirality Associated with Ferroelectric Switching in a High-Temperature Two-Dimensional Perovskite Ferroelectric

Controlling molecular chirality by external stimuli is of great significance in both fundamental research and technological applications. Herein, we report a high-temperature (384 K) molecular ferroelectric of a Cu(II) complex whose spontaneous polarization can be switched associated with flipping of molecular chirality. In this two-dimensional perovskite structure, the inorganic layer is separated by (NH₃(CH₂)₂SS(CH₂)₂NH₃)²⁺ organic cations skewed in a chiral conformation (P- or M-helicity in an individual crystal). As the stereodynamic disulfide bridge determines the molecular dipole moment along the polar axis, the chiral organic cation can be converted to its enantiomer as a consequence of an electric field-induced shift of the S-S moiety relative to its screw axis during the ferroelectric switching. The variation of the molecular chirality is examined with single-crystal X-ray diffraction and circular dichroism spectra. The simultaneous switching of molecular chirality and spontaneous polarization in this perovskite ferroelectric may lead to novel chiral electronic phenomena.

A nickel(ii)-based one-dimensional organic-inorganic halide perovskite ferroelectric with the highest Curie temperature

Organic-inorganic halide perovskites (OIHPs) are very eye-catching due to their chemical tunability and rich physical properties such as ferroelectricity, magnetism, photovoltaic properties and photoluminescence. However, no nickel-based OIHP ferroelectrics have been reported so far. Here, we designed an ABX₃ OIHP ferroelectric (3-pyrrolinium)NiCl₃, where the 3-pyrrolinium cations are located on the voids surrounded by one-dimensional chains composed of NiCl₆-face-sharing octahedra via hydrogen bonding interactions. Such a unique structure enables the (3-pyrrolinium)NiCl₃ with a high spontaneous polarization (P _s) of 5.8 μC cm^-2 and a high Curie temperature (T _c) of 428 K, realizing dramatic enhancement of 112 and 52 K compared to its isostructural (3-pyrrolinium)MCl₃ (M = Cd, Mn). To our knowledge, remarkably, (3-pyrrolinium)NiCl₃ should be the first case of nickel(ii)-based OIHP ferroelectric to date, and its T _c of 428 K (35 K above that of BaTiO₃) is the highest among all reported one-dimensional OIHP ferroelectrics. This work offers a new structural building block for enriching the family of OIHP structures and will inspire the further exploration of new nickel(ii)-based OIHP ferroelectrics.

Halogen Engineering To Realize Regulable Multipolar Axes, Nonlinear Optical Response, and Piezoelectricity in Plastic Ferroelectrics

Compared with uniaxial molecular ferroelectrics, multiaxial ferroelectrics have better application prospects because they are no longer subject to the single-crystal form and have been pursued in recent years. Halogen engineering refers to the adjustment of halogens in materials at the atomic level, which can not only explore multiaxial ferroelectrics but also help to improve piezoelectrics, recently. In this work, we successfully synthesized and characterized three multiaxial plastic ferroelectrics through the precise molecular design from I to Cl, confirming the increase of the number of polar axes of ferroelectrics from 3 to 6, the increase of second-harmonic generation density from 2.1 times to nearly 6 times of monopotassium phosphate, and the increase of piezoelectric coefficient by 140%. This systematic work has proved that halogen engineering can not only enrich the family of multiaxial plastic ferroelectrics but also promote the further development of nonlinear optical and piezoelectric materials.

Halogen engineering of organic-inorganic hybrid perovskites displaying nonlinear optical, fluorescence properties and phase transition

In order to meet the needs of social development, increasing research attention has been paid to multifunctional molecular-based phase-transition materials. The traditional phase-transition materials with a single functional property can be transformed into magnificent ones by adding additional functional properties-for instance photoluminescence and magnetic order- because having two or more functional properties simultaneously greatly broadens the fields of their applications. At present, there are very few multifunctional phase-transition materials showing excellent performance, and the crystal structure design and performance optimization of materials still need to be studied in depth. Herein, we report the development of two organic-inorganic hybrid materials: (MBA)₂ZnI₄ (1, MBA = 4-methoxybenzylammonium) with switchable dielectricity and a high phase-transition temperature (T_c = 359.55 K), and (MBA)₂ZnBr₄ (2) with green luminescence (λ_exc = 314 nm) and nonlinear optical properties (0.75× KDP). A two-dimensional (2D) fingerprint analysis of the Hirshfeld surface plots revealed a significant difference between the hydrogen-bonding interaction before the phase transition and that afterwards. The two compounds were further verified, from energy band structure calculations, to be direct-band-gap semiconductors. In conclusion, this work has provided a viable strategy, involving the application of chemical modifications, for designing various functional materials.

Integrated Reversible Thermochromism, High Tc , Dielectric Switch and Narrow Band Gap in One Multifunctional Ferroic

Organic-inorganic Hybrid (OIH) materials for multifunctional switchable applications have attracted enormous attention in recent years due to their excellent optoelectronic properties and good structural tunability. However, it still remains challenging to fabricate one simple OIH compound with multi-functionals properties, such as dielectric switching, thermochromic properties, semiconductor characteristics and ferroelasticity. Under this context, we successfully synthesized [2-(2-fluorophenyl)ethan-1- ammonium]₂ SnBr₆ (compound 1), which has a higher phase transition temperature of 427.7 K. Additionally, it exhibits a semiconducting property with an indirect band gap of 2.36 eV. Combining ferroelastic, narrow band gap, thermochromic, and dielectric properties, compound 1 can be considered as a rarely reported multi-functional ferroelastic material, which is expected to give inspiration for broadening the applications in the smart devices field.

Axial-Chiral BINOL Multiferroic Crystals with Coexistence of Ferroelectricity and Ferroelasticity

Chirality exists everywhere from natural amino acids to particle physics. The introduction of point chirality has recently been shown to be an efficient strategy for the construction of molecular ferroelectrics. In contrast to point chirality, however, axial chirality is rarely used to design ferroelectrics so far. Here, based on optically active 1,1'-bi-2-naphthol (BINOL), which has been applied extensively as a versatile chiral reagent in asymmetric catalysis, chiral recognition, and optics, we successfully design a pair of axial-chiral BINOL multiferroics, (R)-BINOL-DIPASi and (S)-BINOL-DIPASi. They experience a 2F1-type full ferroelectric/ferroelastic phase transition at a high temperature of 362 and 363 K, respectively. Piezoelectric force microscopy and polarization-voltage hysteresis loops demonstrate their ferroelectric domains and domain switching, and polarized light microscopy visualizes the evolution of stripe-shaped ferroelastic domains. The axial-chiral BINOL building block promotes the generation of the polar structure and ferroelectricity, and the organosilicon component increases the rotational energy barrier and thus the phase transition temperature. This work presents the first axial-chiral high-temperature multiferroic crystals, offering an efficient path for designing molecular multiferroics through the introduction of axial chirality.

Growth, structure, phase transition, thermal properties, and structural dynamics of organic-inorganic hybrid [NH3(CH2)5NH3]ZnCl4 crystal

In this study, the physicochemical properties of [NH₃(CH₂)₅NH₃]ZnCl₄ crystals were investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis, and nuclear magnetic resonance (NMR). The crystals at 300 K had a monoclinic structure with C2/c space group and lattice constants are a = 21.4175 Å, b = 7.3574 Å, c = 19.1079 Å, β = 120.5190°, and Z = 8. Three endothermic peaks at 256, 390, and 481 K were observed in the DSC curve. From the single-crystal XRD patterns, powder XRD patterns, and optical microscopy results based on the temperature change, the phase transition and melting temperatures were determined to be 390 and 481 K, respectively. NMR studies indicated no change in ¹H chemical shifts, but a change in the chemical shifts for C2, located between C1 and C3 of the cation at 340 K. Increase in molecular motion caused an increase in the spin-lattice relaxation time, T_1ρ, at low spinning rates, under magic-angle spinning rate conditions. This crystal showed a minor change in the N-H···Cl hydrogen bond, related to the coordination geometry of the ZnCl₄ anion.

Two host-guest grown ether supramolecules show switchable phase transition, dielectric and second-harmonic generation effect

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.

Design, synthesis and characterization of novel Ni(II) and Cu(II) complexes as antivirus drug candidates against SARS-CoV-2 and HIV virus

This paper describes the structure-based design, synthesis and anti-virus effect of two new coordination complexes, a Ni(II) complex [Ni(L)2] (1) and a Cu(II) complex [Cu(L)2] (2) of (E)-N-phenyl-2-(thiophen-2-ylmethylene) hydrazine-1-carbothioamide(HL). The synthesized ligand was coordinated to metal ions through the bidentate-N, S donor atoms. The newly synthesized complexes were characterized by various spectroscopic and physiochemical methods, powdered XRD analysis and also X-ray crystallography study. Ni(II) complex [Ni(L)2](1) crystallize in orthorhombic crystal system with the space group Pbca with four molecules in the unit cell (a = 9.857(3) Å, b = 7.749(2) Å, c = 32.292(10) Å, α = 90°, β = 90°, γ = 90°, Z= 4) and reveals a distorted square planar geometry. A Hirshfeld surface and 2D fingerprint plot has been explored in the crystal structure of Ni(II) complex [Ni(L)2] (1). Energy framework computational analysia has also been explored. DFT based calculations have been performed on the Schiff base and its metal complexes to study the structure-property relationship. Furthermore, the molecular docking studies of the ligand and its metal complexes with SARS-CoV-2 virus (PDB ID: 7BZ5) and HIV-1 virus (PDB ID: 6MQA) are also investigated. The molecular docking calculations of the Ni(II) complex [Ni(L)2] (1) and a Cu(II) complex [Cu(L)2] (2) with SARS-CoV-2 virus revealed that the binding affinities at inhibition binding site of receptor protein are 9.7 kcal/mol and -9.3 kcal/mol, respectively. The molecular docking results showed that the binding affinities of Ni(II) complex (1) and Cu(II) complex (2) against SARS-CoV-2 virus were found comparatively higher than the HIV-1 virus (-8.5 kcal/mol and -8.2 kcal/mol, respectively). As potential drug candidates, Swiss-ADME predictions analyses are also studied and the results are compared with Chloroquine (CQ) and Hydroxychloroquine (HCQ) as anti-SARS-CoV-2 drugs.

Chlorine Substitution in Spirocyclic Derivatives Triggers SHG Response in Noncentrosymmetric Crystal

Organic-inorganic hybrid phase transition materials with switchable properties have important potential applications in smart devices such as dielectric switches and storage. Nevertheless, it remains challenging to modify molecular structures efficiently to obtain materials simultaneously possessing multiple responsive properties. Herein, different from ordinary halogen substitutions in Metal Halide, we report a halogen regulation design of organic molecular strategy: (ASD) 2 MnBr 4 (ASD=5-azonia-spiro [4.5] decane) to (CASD) 2 MnBr 4 (CASD=8-chloro-5-azonia-spiro [4.5] decane). After organic molecular halogen regulation, the SHG response was excited and the dielectric phase transition temperature ( T c ) has also been greatly improved. Furthermore, under the irradiation of UV lamp, both showed green light with quantum yields above 50%. This work is of great significance for further exploration of multifunctional molecular switch materials through halogen modification strategies.

Synthesis and Characterization of a Displacement-Type Ferroelectric-Ferroelectric Phase Transition Compound [(NH3)(CH2)3(NH3)]2[InBr6]Br·H2O

Ferroelectric materials have aroused the researchers' great interest due to their wide applications. Here, a displacement-type ferroelectric-ferroelectric phase transition material [(NH₃)(CH₂)₃(NH₃)]₂[InBr₆]Br·H₂O (1) with T_c = 143 K was successfully prepared. The ferroelectric phase transition is verified by the characterization techniques such as differential scanning calorimetry, single-crystal structure elucidation, dielectric and ferroelectric measurements. The single-crystal structure elucidation reveals that the displacement and distortion of [(NH₃)(CH₂)₃(NH₃)]²⁺ cations lead to the phase transition from Cmc2₁ to Pca2₁. The spontaneous polarizations at 293 and 133 K are 0.15 and 0.12 μC·cm^-2, respectively. We expect that this work will help in further exploration of some new ferroelectric materials.

Ferroelectric coordination metal complexes based on structural and electron dynamics

Ferroelectrics that display electrically invertible polarisation are attractive materials because of their potential for wide-ranging applications. To date, considerable effort has thus been devoted towards developing ferroelectric materials, particularly those comprising organic/inorganic compounds. In these systems, structural dynamics such as atomic displacement and reorientation of polar ions/molecules play a key role in the generation of reversible spontaneous polarisation. Although there are many reports concerned with organic/inorganic ferroelectrics, ferroelectrics based on coordination metal complexes have been largely unexplored despite their often unique electronic and spin state properties. In this feature article, we discuss recent progress involving coordination metal complex-based ferroelectrics where the reversible polarisation originates not only from structural dynamics (represented by proton transfer, molecular motion, and liquid crystalline behaviour) but also from electron dynamics (represented by electron transfer and spin crossover phenomena) occurring at the metal centre. Furthermore, unique synergy effects (i.e. magnetoelectric coupling) resulting from the structural and electron dynamics are described. We believe that this review pertaining to ferroelectric coordination metal complexes provides new insights for fabricating further advanced functional materials such as multiferroics and spintronics.

Two-Step Dielectric Responsive Organic-Inorganic Hybrid Material with Mid-Band Light Emission

Hybrid organic-inorganic perovskite (HOIP) have received tremendous scientific attention because of the phase transition and photovoltaic properties. However, achieving the special perovskite structure with both two-step dielectric response and luminescence characteristics is rarely reported. Herein, we report an organic-inorganic hybrid perovskite, [(BA)₂  ⋅ PbI₄ ] (Compound 1, BA=n-butylamine) by introducing flexible organic cations (HBA⁺ ), with direct mid-band gap as 2.28 eV. Interestingly, this material exhibits two-step reversible dielectric response at 350 K and 460 K (in heating process), respectively. Besides, the photoluminescence was found: it emits charming green light under 365 nm lamp (Photoluminescence quantum yield is 9.52 %). The outstanding two-step dielectric response and luminescence characteristics of this compound might pave the way for the application of dielectric and ferroelectric functional materials in temperature sensors and mechanical switches.

Ferroelasticity in Organic-Inorganic Hybrid Perovskites

Molecular ferroelastics have received particular attention for potential applications in mechanical switches, shape memory, energy conversion, information processing, and solar cells, by taking advantages of their low-cost, light-weight, easy preparation, and mechanical flexibility. The unique structures of organic-inorganic hybrid perovskites have been considered to be a design platform for symmetry-breaking-associated order-disorder in lattice, thereby possessing great potential for ferroelastic phase transition. Herein, we review the research progress of organic-inorganic hybrid perovskite ferroelastics in recent years, focusing on the crystal structures, dimensions, phase transitions and ferroelastic properties. In view of the few reports on molecular-based hybrid ferroelastics, we look forward to the structural design strategies of molecular ferroelastic materials, as well as the opportunities and challenges faced by molecular-based hybrid ferroelastic materials in the future. This review will have positive guiding significance for the synthesis and future exploration of organic-inorganic hybrid molecular ferroelastics.

Solvent Selective Effect Occurs in Iodinated Adamantanone Ferroelectrics

Organic ferroelectrics, as a type of crystalline compound, are generally solution processing. However, for most crystalline compounds, the changing of solvent would not influence the crystalline phase, let alone their physical performance. Here, the solvent selective effect occurs in the iodinated adamantanone ferroelectrics. By changing the solvent with different polarities, the ferroelectric crystals can be induced in two different phases, which is unprecedented to the knowledge. More strikingly, this solvent-induced transformation could realize the physical performance optimization in the orthorhombic phase (orth-I-OA, obtained from ethanol) with a stronger second harmonic generation (SHG) response, greater piezoelectric coefficient d₃₃ of 5 pC N^-1 , and larger spontaneous polarization (P_s ) of 3.43 µC cm^-2 than those of monoclinic one (mono-I-OA, obtained from ethyl acetate). Such an intriguing phenomenon might be closely related to solvent polarity. Based on the quantitative and qualitative analyses, the similar interaction energies of these two phases suggest that their transformation could be easily realized via changing the solvent. This work provides new insights into the chemical design and performance optimization of organic ferroelectrics.

Advances in physicochemical characterization of lead-free hybrid perovskite [NH3(CH2)3NH3]CuBr4 crystals

To support the development of eco-friendly hybrid perovskite solar cells, structural, thermal, and physical properties of the lead-free hybrid perovskite [NH3(CH2)3NH3]CuBr4 were investigated using X-ray diffraction (XRD), differential scanning calorimetry, thermogravimetric analysis, and nuclear magnetic resonance spectroscopy. The crystal structure confirmed by XRD was monoclinic, and thermodynamic stability was observed at approximately 500 K without any phase transition. The large changes in the 1H chemical shifts of NH3 and those in C2 close to N are affected by N-H∙∙∙Br hydrogen bonds because the structural geometry of CuBr4 changed significantly. The 1H and 13C spin-lattice relaxation times (T1ρ) showed very similar molecular motions according to the Bloembergen-Purcell-Pound theory at low temperatures; however, the 1H T1ρ values representing energy transfer were about 10 times lesser than those of 13C T1ρ. Finally, the 1H and 13C T1ρ values of [NH3(CH2)3NH3]MeBr4 (Me = Cu, Zn, and Cd) were compared with those reported previously. 1H T1ρ was affected by the paramagnetic ion of the anion, while 13C T1ρ was affected by the MeBr4 structure of the anion; 13C T1ρ values in Me = Cu and Cd with the octahedral MeBr6 structure had longer values than those in Me = Zn with the tetrahedral MeBr4 structure. We believe that these detailed insights on the physical properties will play a crucial role in the development of eco-friendly hybrid perovskite solar cells.

Dehydration-activated structural phase transition in a two-dimensional hybrid double perovskite

As a feasible lead-free scheme, organic-inorganic hybrid double perovskites show many excellent properties, including ferroelectricity, ferroelasticity, self-powered circularly polarized light detection and so on. In this work, the solid-to-solid structural phase transition of a two-dimensional hybrid double perovskite (CHA)₄CuBiI₈ was successfully activated via the dehydration of (CHA)₄CuBiI₈·H₂O, which was proven by differential scanning calorimetry (DSC) and temperature-dependent dielectric measurements. Using variable-temperature single-crystal X-ray diffractometry, the cause behind the phase transition of (CHA)₄CuBiI₈ was determined to be the overall coordination of distortion and movement of the inorganic skeleton and thermal deformation of the cationic structure. In addition, the substance after dehydration shows good stability in multiple reversible switching during dielectric tests. The interesting dehydration-activated results of the material contribute towards a further expansion of the properties and potential application of hybrid double perovskites.

Voltage controlled bio-organic inverse phototransistor

Thin films of poly-d-lysine act as polar organic and are also light sensitive. The capacitance-voltage, current-voltage, and transistor behavior were studied to gauge the photoresponse of possible poly-d-lysine thin film devices both with and without methylene blue as an additive. Transistors fabricated from poly-d-lysine act as inverse phototransistors, i.e., the on-state current is greatest in the absence of illumination. The poly-d-lysine thin film capacitance and the transistor current decrease with illumination, both with and without methylene blue as an additive. This suggests that the unbinding of photo exciton is significantly hindered in this system which is supported by the significant charge carrier lifetime for poly-d-lysine films both with and without methylene blue. For the majority carrier, the transistor geometry appears to depend on the gate voltage; in other words, the majority carrier depends on the polarization of the poly-d-lysine films, both with and without methylene blue as an additive.

Metal ion modulation triggers dielectric double switching and green fluorescence in A2MX4-type compounds

Multifunctional switching materials show great potential for applications in sensors, smart switches, and other fields due to their ability to integrate different physical channels in one single device. However, multifunctional responsive materials with multiple switching and luminescence properties have rarely been reported. Here, we report three organic-inorganic hybrids: [TMAA]₂[CoCl₄] (compound 1), [TMAA]₂[CdBr₄] (compound 2) and [TMAA]₂[MnCl₄] (compound 3). Compound 1 and compound 2 undergo two reversible phase transitions at high temperature (328.95/359.25 K and 350.45/393.15 K, respectively). Since the inorganic skeleton has a strong influence on the luminescence properties of such structured substances, Cd and Co were replaced with Mn, after which compound 3 was obtained as expected. The above strategy triggered bright green luminescence with a quantum yield of 35.19%, and significantly increased the phase transition temperature of compound 3 to above 400 K. The above results show that the regulation of the inorganic skeleton provides a new strategy for researchers to develop dual phase change/luminous materials.

An organic plastic ferroelectric with high Curie point

Plastic ferroelectrics, featuring large entropy changes in phase transitions, hold great potential application for solid-state refrigeration due to the electrocaloric effect. Although conventional ceramic ferroelectrics (e.g., BaTiO3 and KNbO3) have been widely investigated in the fields of electrocaloric material and catalysis, organic plastic ferroelectrics with a high Curie point (T c) are rarely reported but are of great importance for the sake of environmental protection. Here, we reported an organic plastic ferroelectric, (-)-camphanic acid, which crystallizes in the P21 space group, chiral polar 2 (C2) point group, at room temperature. It undergoes plastic paraelectric-to-ferroelectric phase transition with the Aizu notation of 23F2 and high T c of 414 K, showing large entropy gain (ΔS t = 48.2 J K-1 mol-1). More importantly, the rectangular polarization-electric field (P-E) hysteresis loop was recorded on the thin film samples with a large saturated polarization (P s) of 5.2 μC cm-2. The plastic phase transition is responsible for its multiaxial ferroelectric feature. This work highlights the discovery of organic multiaxial ferroelectrics driven by the motive of combining chirality and plastic phase transition, which will extensively promote the practical application of such unique functional materials.

Thermal-driven unusual dual SHG switching with wide SHG-active step triggered by inverse symmetry breaking

Solid nonlinear optical (NLO) materials with switchable second-harmonic generation (SHG) on/off state show a strong potential application in photo-electronic devices. Sustained progress has been made through the persistent exploration of...

A new crown-ether clathrate [15-crown-5][Y(NO3)2(H2O)5][NO3] with switchable dielectric constant behaviour

A crown-ether clathrate employing a rare-earth ion as the central metal ion was developed, and shown to display switchable dielectric behaviours around a temperature of about 230 K.

Two quasi-spherical molecules [1,4-diazabicyclo(3.2.2)nonane]X (X = ClO4, ReO4) exhibit switchable phase transition, dielectric and second-harmonic-generation properties

Two quasi-spherical molecules [3.2.2-Hdabc]X (1,4-diazabicyclo[3.2.2]nonane = 3.2.2-dabcn, X = ClO4, ReO4) with a high phase transition temperature exhibited switchable phase transition as well as dielectric and SHG properties.

2D lead-free organic–inorganic hybrid exhibiting dielectric and structural phase transition at higher temperatures

A novel switchable molecular dielectric material [3-3-difluorocyclobutylammonium]2CdCl4 was synthesized. It shows a reversible phase transition at 353.95 K and rapid switching and reversibility between high and low dielectric states for several cycles.

Thermally stimuli-responsive materials with transformable double channels of nonlinear optical and dielectric

Organic-inorganic hybrid materials have received extensive attention and in-depth research in the past few decades due to their superior properties and potential applications in storage, sensing, dielectric switches, actuators and...