Organic ferroelectrics are highly desirable for their light weight, mechanical flexibility and biocompatibility. However, the rational design of organic ferroelectrics has always faced great challenges. Anilinium bromide (AB) has two structures reported in the Cambridge Crystallographic Data Centre, which might be an mmmF2/m type ferroelastic (AB-1). When we studied its ferroelasticity, we were surprised to discover that there was another crystal (AB-2) in H2 O besides this one, and they were very difficult to separate. By changing the solvent, we found that AB-1 crystals could be formed in ethanol, where ferroelastic domains were visualized by polarized light microscopy, and AB-2 crystals could be obtained from various crystallization solvents of methanol, isopropanol, N-butanol, acetonitrile, dimethyl sulfoxide, and N,N-dimethylformamide, which undergo a ferroelectric phase transition with mm2Fm, showing clear ferroelectricity in two phases. To our knowledge, the regulation of ferroelasticity to ferroelectricity by solvent selective effect is unprecedented in the field of ferroelectrics. This work reveals the important role of solvent effect in organic ferroelectrics.
1,4-Diazabicyclo[2.2.2]octane (dabco) and its derivatives have been extensively utilized as building units of excellent molecular ferroelectrics for decades. However, the homochiral dabco-based ferroelectric remains a blank. Herein, by adding a methyl (Me) group accompanied by the introduction of homochirality to the [H2 dabco]2+ in the non-ferroelectric [H2 dabco][TFSA]2 (TFSA=bis(trifluoromethylsulfonyl)ammonium), we successfully designed enantiomeric ferroelectrics [R and S-2-Me-H2 dabco][TFSA]2 . The two enantiomers show two sequential phase transitions with transition temperature (Tc ) as high as 405.8â K and 415.8â K, which is outstanding in both dabco-based ferroelectrics and homochiral ferroelectrics. To our knowledge, [R and S-2-Me-H2 dabco][TFSA]2 are the first examples of dabco-based homochiral ferroelectrics. This finding opens an avenue to construct dabco-based homochiral ferroelectrics and will inspire the exploration of more eminent enantiomeric molecular ferroelectrics.
For a century ferroelectricity has attracted widespread interest from science and industry. Inorganic ferroelectric ceramics have dominated multibillion dollar industries of electronic ceramics, ranging from nonvolatile memories to piezoelectric sonar or ultrasonic transducers, whose polarization can be reoriented in multiple directions so that they can be used in the ceramic and thin-film forms. However, the realization of macroscopic ferroelectricity in the polycrystalline form is challenging for molecular ferroelectrics. In pursuit of low-cost, biocompatible, and mechanically flexible alternatives, the development of multiaxial molecular ferroelectrics is imminent. Here, from quinuclidinium perrhenate, we applied fluorine substitution to successfully design a multiaxial molecular ferroelectric, 3-fluoroquinuclidinium perrhenate ([3-F-Q]ReO4), whose macroscopic ferroelectricity can be realized in both powder compaction and thin-film forms. The fluorination effect not only increases the intrinsic polarization but also reduces the coercive field strength. More importantly, it is also, as far as we know, the softest of all known molecular ferroelectrics, whose low Vickers hardness of 10.5 HV is comparable with that in poly(vinylidene difluoride) (PVDF) but almost 2 orders of magnitude lower than that in BaTiO3. These attributes make it an ideal candidate for flexible and wearable devices and biomechanical applications.
Materials with circularly polarized luminescence (CPL) activity have immense potential applications in molecular switches, optical sensors, information storage, asymmetric photosynthesis, 3D optical displays, biological probe, and spintronic devices. However, the achiral architectures of most of the luminophores severely limit their practical needs. Within this context, molecular ferroelectrics with striking chemical variability and structure-property flexibility bring light to the assembly of CPL-active ferroelectric materials. Herein, we report organic-inorganic perovskite enantiomorphic ferroelectrics, (R)- and (S)-3-(fluoropyrrolidinium)MnBr3, undergoing a 222F2-type ferroelectric phase transition at 273 K. Their mirror relationships are verified by both single-crystal X-ray diffraction and vibrational circular dichroism (VCD). Furthermore, the corresponding Cotton effect for two chiral crystals was captured by mirror CPL activity. This may be assigned to the inducing interaction between the achiral luminescent perovskite framework and chiral organic components. As far as we know, this is the first molecular ferroelectric with CPL activity. Accordingly, this will inspire intriguing research in molecular ferroelectrics with CPL activity and holds great potential for the development of new optoelectronic devices.
Temperature-responsive materials with switching physical properties have been widely researched. Among them, the switchable dielectric perovskite materials show potential applications in the electrical and electronic industries and even the intelligence industries. However, perovskite oxides and hybrid organic-inorganic perovskites, as the most representative switchable dielectric materials, are limited by bad biocompatibility. Herein, we report temperature-dielectric-responsive metal-free perovskite (H2dabco)(NH4)[BF4]3 constructed by the strategy of substituting the B site in the general formula ABX3 (doubly protonated 1,4-diazabicyclo[2.2.2]octane = H2dabco). Meanwhile, structurally similar hybrid material (H2dabco)Rb[BF4]3 was designed as a control. They exhibit similar phase-transition characteristics and dielectric response behaviors around 333 K. More interestingly, the ordered-disordered transformation of their organic "spherical" cations (H2dabco) was deemed to produce their phase transitions and dielectric response switching. Given its ability to generate a dielectric response, (H2dabco)(NH4)[BF4]3 will show the potential application of metal-free perovskite in a future thermal sensing device.
Piezoelectric sensors that can work under various conditions with superior performance are highly desirable with the arrival of the Internet of Things. For practical applications, a large piezoelectric voltage coefficient g and a high Curie temperature Tc are critical to the performance of piezoelectric sensors. Here, we report a two-dimensional perovskite ferroelectric (4-aminotetrahydropyran)2PbBr4 [(ATHP)2PbBr4] with a saturated polarization of 5.6 µC cm-2, high Tc of 503 K [above that of BaTiO3 (BTO, 393 K)], and extremely large g33 of 660.3 × 10-3 V m N-1 [much beyond that of Pb(Zr,Ti)O3 (PZT) ceramics (20 to 40 × 10-3 V m N-1), more than 2 times higher than that of poly(vinylidene fluoride) (PVDF, about 286.7 × 10-3 V m N-1)]. Combined with the advantages of molecular ferroelectrics, such as light weight, easy and environmentally friendly processing, and mechanical flexibility, (ATHP)2PbBr4 would be a competitive candidate for next-generation smart piezoelectric sensors in flexible devices, soft robotics, and biomedical devices.
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, [(CH3 )3 NCH2 CH3 ]2 MnCl4 (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.
The significant Tc enhancement of 110 K in [N-fluoromethyldabconium] triiodide lead caused by the promising design of H/F substitution is the first and unprecedented, opening up an applicable and universal strategy to effectively regulate the Tc working temperature in phase transition 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)4Pb3Br10 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.
In this paper, three zero-dimensional organic-inorganic hybrid compounds [(CH3)3S]2[CdBr4] (1), [(CH3)3S]2[MnBr4] (2) and [(CH3)3S]2[ZnBr4] (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 [(Me3)3S]+ and [MBr4]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 P212121. 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.
The crystal structures of three quinuclidine-based compounds, namely (1-azabicyclo[2.2.2]octan-3-ylidene)hydrazine monohydrate, C7H13N3·H2O (1), 1,2-bis(1-azabicyclo[2.2.2]octan-3-ylidene)hydrazine, C14H22N4 (2), and 1,2-bis(1-azoniabicyclo[2.2.2]octan-3-ylidene)hydrazine dichloride, C14H24N42+·2Cl- (3), are reported. In the crystal structure of 1, the quinuclidine-substituted hydrazine and water molecules are linked through N-H...O and O-H...N hydrogen bonds, forming a two-dimensional array. The compound crystallizes in the centrosymmetric space group P21/c. Compound 2 was refined in the space group Pccn and exhibits no hydrogen bonding. However, its hydrochloride form 3 crystallizes in the noncentrosymmetric space group Pc. It shows a three-dimensional network structure via intermolecular hydrogen bonding (N-H...C and N/C-H...Cl). Compound 3, with its acentric structure, shows strong second harmonic activity.
Organic-inorganic hybrid perovskite-type multiferroics have attracted considerable research interest owing to their fundamental scientific significance and promising technological applications in sensors and multiple-state memories. The recent achievements with divalent metal dicyanamide compounds revealed such malleable frameworks as a unique platform for developing novel functional materials. Herein, two 3D organic-inorganic hybrid perovskites [Et3 P(CH2 )2 F][Mn(dca)3 ] (1) and [Et3 P(CH2 )2 Cl][Mn(dca)3 ] (2) (dca=dicyanamide, N(CN)2 - ) are presented. Accompanying the sequential phase transitions, they display a broad range of intriguing physical properties, including above room temperature ferroelastic behavior, switchable dielectricity, and low-temperature antiferromagnetic ordering (Tc =2.4â K for both 1 and 2). It is also worth noting that the spontaneous strain value of 1 is far beyond that of 2 in the first ferroelastic phase, as a result of the precise halogen substitution. From the point view of molecular design, this work should inspire further exploration of multifunctional molecular materials with desirable properties.
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.
[C6N2H18][SbI5] (1), a novel metal halide semiconductor with dielectric relaxation behavior, has been successfully synthesized, in which the cavities between the one-dimensional [SbI5] n2- polyanions are occupied by 2-methyl-1,5-pentanediammonium (2-MPDA) cations. 1 undergoes a reversible solid-state phase transition at TC = 192.7 K and shows a step-like dielectric anomaly. Interestingly, above TC, 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, [(CH3 )3 S]3 [Bi2 Br9 ](1) is a brilliant semiconducting organic-inorganic hybrid perovskite-type non-ferroelectric piezoelectric with excellent piezoelectricity. Strikingly, the value of the piezoelectric coefficient d33 is estimated as ≈18â 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 ≈2.58â eV that is lower than the reported value of 3.37â 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.
Bistable optical-electrical duplex switches represent a class of highly desirable intelligent materials because of their potential applications in the fields of next-generation flexible devices. However, controllable photoelectric switchable materials with high-performance dielectric-switching and optical-switching properties are still scarce, with triplex bistable switches being rarely reported. Herein, a novel optoelectronic triple-functional organic-inorganic material, 5-azonia-spiro[4,4]nonane tetrabromomanganese (1, [ASN]2[MnBr4], ASN = (CH2)4N(CH2)4), which undergoes a reversible solid-state phase transition around 327 K and exhibits a recognizable second harmonic generation (SHG) effect between SHG-on and SHG-off states, has been successfully synthesized and grown as block crystals. Intriguingly, the bromine-doped crystal can exhibit intense green luminescence with a high quantum yield of 13.07% under UV excitation, extending its application in the field of photoelectric seamless integration and/or flexible multifunctional devices.
Both 3D organic-inorganic perovskites ([Et3P(CH2)2Cl][Cd(dca)3] (1) and [Et3P(CH2)2F][Cd(dca)3] (2) [dca = dicyanamide, N(CN)2-]) display two sequentially reversible high-temperature phase transitions and switchable dielectric properties. Through halogen substitution, 1 shows exceptional switching behaviour of second harmonic generation effects and remarkably 2 represents the first above-room-temperature 3D ferroelastic material characterized by two ferroelastic phases.
Inorganic perovskite ferroelectrics are widely used in nonvolatile memory elements, capacitors, and sensors because of their excellent ferroelectric and other properties. Organic ferroelectrics are desirable for their mechanical flexibility, low weight, environmentally friendly processing, and low processing temperatures. Although almost a century has passed since the first ferroelectric, Rochelle salt, was discovered, examples of highly desirable organic perovskite ferroelectrics are lacking. We found a family of metal-free organic perovskite ferroelectrics with the characteristic three-dimensional structure, among which MDABCO (N-methyl-N'-diazabicyclo[2.2.2]octonium)-ammonium triiodide has a spontaneous polarization of 22 microcoulombs per square centimeter [close to that of barium titanate (BTO)], a high phase transition temperature of 448 kelvins (above that of BTO), and eight possible polarization directions. These attributes make it attractive for use in flexible devices, soft robotics, biomedical devices, and other applications.
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]], {(C4H12N2)[NaI3]}n, 1, and catena-poly[tris(piperazinediium) [[triiodidosodium]-µ-iodido] triiodide monohydrate], {(C4H12N2)3[NaI4]I3·H2O}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 NaI 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 NaI6 octahedra stretching along the direction of the three axes, and each piperazinediium dication is enclosed in the NaI3 perovskite cage. However, in 2, each NaI 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.
Molecular bistable dielectric switches represent a class of highly desirable intelligent materials due to their sensitive switchable responses, simple and environmentally friendly processing, light weights, and mechanical flexibility. However, most of these switches can only work at a very low temperature, extremely limiting their potential applications. Herein, three layered organic-inorganic hybrid perovskite-type compounds of the general formula A2BX4, [NH3(CH2)2Cl]2[CdCl3Br] (1), [NH3(CH2)2Cl]2[CdCl4] (2) and [NH3(CH2)2Cl]2[CdBr4] (3), which display sensitive dielectric switching reversibility and remarkable switching anti-fatigue, have been successfully designed. Differential scanning calorimetry and dielectric measurements for 1 confirm its reversible phase transition at around 166 K. Through anion modulation, the phase transition temperatures of 2 and 3 can be greatly improved up to 237 K and 254 K, respectively. Structural analysis discloses that the phase transition temperature's shifts may result from the differences among the inorganic frameworks. Moreover, due to the significant order-disorder transitions of ammonium cations, the permittivities of 1, 2 and 3 change abruptly at around the phase transition points, making them excellent stimuli-responsive electrical switches. Such an anion-modulated method will open up new possibilities of highly efficiently tuning the phase transition temperature of molecular bistable dielectric switches.
