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By the replacement of halogen anion, three new multifunctional organic-inorganic hybrid perovskites (thiomorpholinium)PbX3 (X = Cl, Br, I) were successfully synthesized and underwent reversible structural transformation above room temperature, accompanied by the anomalous change of dielectric constant. With the adjustment of the halogen anion from Cl to I in the inorganic skeleton, the space group is transformed from centrosymmetric space group P21/c ((thiomorpholinium)PbCl3) to chiral one P212121 ((thiomorpholinium)PbBr3, (thiomorpholinium)PbI3) at room temperature. The ordered-disordered transition of organic cations and the change of hydrogen bonds with the increase of temperature lead to above-room-temperature phase transitions. Ultraviolet absorption and second-harmonic generation (SHG) measurements confirmed that both the band gap and SHG activity of (thiomorpholinium)PbX3 (X = Cl, Br, I) crystals were tunable. The band gaps reveal a broadening trend with 3.532 eV, 3.410 eV and 3.175 eV along the Cl → Br → I series. This work provides an effective molecular design for multifunctional organic-inorganic perovskites.

Two organic–inorganic hybrid compounds [(CH3)3CN(CH3)2CH2F]2[MBr4] (M = Cd and Zn) undergo ferroelastic phase transitions. The substitution of metal center Cd with Zn of inorganic anions regulate the ferroelastic phase transitions.

Switchable nonlinear optical (NLO) materials have aroused broad interest on account of their captivating optical and electronic properties. We demonstrate a novel perovskite-type crystal with exceptional hydrogen bond interactions that are associated with the onset of reorientational motions of organic cations and thus induce the occurrence of two successive phase transitions to be a two-step NLO switch. This finding affords an alternative approach for the design and assembly of switchable NLO materials.

Two new mixed-ligand-based compounds, namely [Co(1,3-pde)(4-bpmh)]n (1) and [Zn3(3,3���-bpdc)3(4-bpmh)1.5]n (2) (1,3-H2pde = 1,3-phenylenediacetic acid, 3,3���-H2bpdc = biphenyl-3,3'-dicarboxylic acid, 4-bpmh = N,N-bis-pyridin-4-ylmethylene-hydrazine) have been prepared under hydrothermal conditions. The obtained compounds were determined by singe crystalX-ray diffraction analyses, elemental analyses, powder X-ray diffraction analyses and thermogravimetric analyses. Moreover, the photocatalytic activity of 1 and luminescent property of 2 have also been investigated. This presented research estimate their treatment activity of the polycystic ovary syndrome, also the mechanism was measured as well. Firstly, a relative expression of the estrogen receptor on the ovarian epithelial cells was determined with real time RT-PCR. In addition, the amount of progesterone of the plasma was measured with ELISA detection kit after indicated treatment.

The remarkable material stability and structural diversity of two-dimensional (2D) organic-inorganic hybrid perovskites (OIHPs) constitute a vast available library of versatile materials. In particular, ferroelastic property, for which the spontaneous strain can be transformed by applying mechanical stress, is very promising for extensive nanotechnological applications. However, integrating ferroelastic property into 2D OIHPs is still in its infancy. Herein, we designed two new 2D OIHPs (C3H5CH2NH3)2[MCl4] (M = Mn for 1 and Cd for 2), which undergo reversible ferroelastic phase transitions with an Aizu expression 4/mmmFmmm. The templating influence of the more distorted inorganic framework on the disordering of organic cations and the stronger hydrogen bonds has a key role in the striking improvement of Curie temperature from 246 K in 1 to 273 K in 2. Meanwhile, the minimized alteration of structural motif ensures the well maintaining of the ferroelastic performance in the forms of crystals and thin films, as demonstrated by the identifiable evolution of domain structures. This work will provide a fertile new ground for enlarging the limited number of 2D ferroelastic OIHPs with better practical utility.

Two-dimensional organic-inorganic hybrid perovskites (OIHPs) have gained attention as a result of their flexibility and adjustability of the structure. However, the large band gap of two-dimensional perovskites limits their application in the photoelectric field. In the present work, we report a two-dimensional organic-inorganic hybrid compound of (C7H18N2)PbI4 (1) with a narrow band gap, which consists of [PbI4]2-n layers and N-(2-aminoethyl)piperidinium cations. 1 exhibits semiconducting properties with a narrow optical band gap of ∼2.02 eV and a photoelectric response with a ratio of photocurrent to dark current of ∼100. In addition, it exhibits a reversible solid-state phase transition at 228 K. This finding should inspire research into more 2D layered OIHPs with the combination of phase transition and semiconductor properties.

Solid solution has long been used in inorganic oxides to modulate structures and physical properties. In contrast, for molecular solid solutions, new and unexpected properties can emerge because of...

Stimulus responsive materials can provide a variety of desirable properties in one equipment unit, such as optoelectronic devices, data communications, actuators, memories, sensors and capacitors. However, it remains a large challenge to design such stimulus responsive materials, especially functional materials having both dielectric switch and second harmonic generation (SHG). Here, a new stimuli-responsive switchable material [(CH3)3N(CH2)2Cl]2[Mn(SCN)4(H2O)2] was discovered as a potential second-harmonic generation (SHG) dielectric switch. It is worth noting that it has SHG characteristics before and after undergoing reversible high-temperature phase transitions. In this work, we successfully refined the tetramethylammonium cation to obtain a quasi-spherical cation, which is tetramethylchloroethylamine (TMCEM) cation. By substituting H with a halogen, the increased steric hindrance of the molecular makes energy barrier increased, resulting in the reversible high-temperature phase transition. At the same time, the interactions of quasi-spherical cations and [Mn(SCN)4(H2O)2]2− anions affect a non-centrosymmetric structure to induce the SHG effect. These findings provide a new approach to design novel functional switch materials.

Nonlinear optical (NLO) switches and piezoelectric materials have drawn widespread attention benefiting from the enormous potential applications in photonic technology devices and smart sensors. Herein, we report two lead-free organic–inorganic hybrid materials, [(R)-3-hydroxy-pyrrolidinium]2SbBr5 (1) and [(R)-3-hydroxy-pyrrolidinium]5Sb4Br17 (2), in a ratio of 3 : 2 and 1 : 1 of (R)-pyrrolidin-3-ol and SbBr3, respectively. The introduction of homochiral cations ensures that 1 and 2 crystallize in non-centrosymmetric and chiral space groups, realizing the combination of piezoelectricity and second harmonic generation (SHG) properties. Moreover, the different proportions of reagents endow the two compounds with diverse structures and physical properties. Remarkably, 1 presents a novel bi-step SHG switch and demonstrates semiconductor properties with a band gap of 2.49 eV. 2 displays a SHG switch and a band gap of 3.00 eV, together with a piezoelectric response (d22 = 22 pC N−1). These findings offer a valuable way to design organic–inorganic hybrid materials combining multiple splendid physical properties and stimulate further exploration of the mutual relations between structures and physical properties.

A one-dimensional coordination polymer [(C2H4OH)C4H9NS]CdCl3 (1) with flexible N-(2-hydroxyethyl)thiomorpholinium cations coordinating to central metal Cd crystallized in a chiral space group P212121 and showed a reversible phase transition at 174.4/162.8 K, which corresponded to the second harmonic generation (SHG) activity and dielectric switching. The introduction of a thioether group enables 1 to adsorb Pd(II) metal ions and the SHG signal and dielectric switching disappeared after adsorption; hence, Pd(II) adsorption can be monitored by the measurements of SHG and dielectric switching. This study emphasizes the advantages of introducing functional groups into the phase transition materials and presents a new approach to design multifunctional materials.

Molecular phase transition compounds have become a hot research area in recent years because of their potential as functional materials, such as ferroelectrics, ferroelastics, dielectric switches, etc. However, materials combining switchable dielectric properties and ferroelasticity are still rare. Here, we reported an organic-inorganic hybrid perovskite, [CPtmp][Cd(SCN)3] (1) ([CPtmp]+ is a cyclopentyltrimethylphosphonium cation), with a potential ferroelastic property. This material undergoes three structural phase transitions at 247/226, 335/312, and 349/341 K (upon heating/cooling). The successive phase transitions are mainly caused by the stepwise ordering of [CPtmp]+ cations and the concomitant deformation of [Cd(SCN)3]- anionic chains revealed by structural analyses, which triggers the double-step dielectric switching in 1 as well. These results would inspire further exploration on molecular dielectric switches with ferroelastic properties.

The one-dimensional (1D) ABX3-type perovskite [(CH3)3PCH2F]CdCl2Br (1) has been obtained on the basis of the design of an organic-inorganic hybrid. Strikingly, it experiences sequential phase transitions at around 295 and 336 K, respectively. Given the noticeable steplike dielectric anomalies in the vicinity of 295 K, 1 is identified as a promising dielectric-switchable material. According to the single-crystal structure analysis, the order-to-disorder transformation of the [(CH3)3PCH2F]+ cation is the main reason for the phase transitions and the change of space group from the orthorhombic Pnma (No. 62) to the hexagonal P63/m (No. 176). This design of a perovskite structure will inspire more advances in the ever-growing field of switchable functional materials.

In the last decade, hybrid materials have received widespread attention. In particular, hybrid lead halide perovskite-type semiconductors are very attractive owing to their great flexibility in band gap engineering. Here, by using precise molecular modifications, three one-dimensional perovskite-type semiconductor materials are designed and obtained: [Me3 PCH2 X][PbBr3 ] (X=H, F, and Cl for compounds 1, 2, and 3, respectively). The introduction of a heavier halogen atom (F or Cl) to [Me4 P]+ increases the potential energy barrier required for the tumbling motion of the cation, hence achieving the transformation of the phase transition temperature from low temperature (192 K) to room temperature (285 K) and high temperature (402.3 K). Moreover, the optical band gaps reveal a broadening trend with 3.176 eV, 3.215 eV, and 3.376 eV along the H→F→Cl series, which is attributed to the formation of the structural distortion.

Molecular perovskite materials have recently attracted extraordinary interest from the academic community owing to their excellent multifunctional properties. Nevertheless, although massive efforts have been made, molecular ferroelastics with three-dimensional (3D) perovskite structures are still rare. Herein, we report two 3D organic-inorganic hybrid perovskites [(2-hydroxy-propyl)-tripropyl-ammonium][Mn(dca)3] (1) and [(2-hydroxy-1-methyl-ethyl)-tripropyl-ammonium] [Mn(dca)3] (2) [dca = dicyanamide, N(CN)2]. The different position of the chiral center results in a tremendous difference in the properties. Compound 1 displays only one phase transition; however, intriguingly, 2 has three phase transitions and represents ferroelastic behavior with exceptional two-step switching of quadratic nonlinear optical (NLO) properties. To the best of our knowledge, this is the first molecular ferroelastic with two-step switching of quadratic NLO properties. The results demonstrate that the molecular chiral design works, and this finding opens up a new avenue to designing multifunctional molecular perovskite materials.

The isotope effect usually brings improved performance or new features, such as KD2PO4 and SrTi18O3 inducing a higher phase transition temperature (Tc) and ferroelectricity, respectively. However, ...

Optic-electric responsive materials have attracted much attention for their applications in temperature-sensing, actuators, and memory switches. However, it is a challenge to integrate various functions to form multifunctional responsive materials. As molecule-based hybrid materials usually consist of organic and inorganic components, the introduction of multiple functions can be achieved through structural construction. Thus far, even though full-temperature cover is required for device applications, full-temperature covered multi-switchable hybrid materials have rarely been successfully synthesized. Herein, the dynamic [(CH3)3NOH]+ cation and luminous center Mn(II) were introduced to form a hybrid material [(CH3)3NOH][MnCl3], showing multiple temperature-responsive behaviors. Upon temperature change, it exhibits multi-state dielectric switching response and intensity or peak shift response of luminous in full-temperature range (low, room, and high temperatures). These responsive behaviors are triggered by the motion or reorientation of [(CH3)3NOH]+ cations and inorganic framework. Overall, the switchable photoelectric material has potential applications in multiple encrypted storage and sensor devices.

Dual phase transition/switch materials are a critical cornerstone of information storage and sensing. However, they are difficult to design successfully, and compared with materials showing single-switchable phase transitions, the dual ones retain many challenges by far. Therefore, the significance of a general strategy is far greater than an accidental success. Here, an efficient strategy combining branchlike Et

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.

A method of service quality from tourists’ perception based on improved evidence theory is proposed, because it is difficult to obtain the effective service quality of travel agency O2O model by us...

Smart stimulus-responsive materials, which can automatically respond to external stimuli (thermal/optical/electrical) and rapidly switch between high/low states (switch ON/OFF), have been an important feature in high-tech fields such as smart electronic devices, the Internet of things, robots and so on. However, the effective design and development of these materials with simple fabrication methods, multiple response modes and logical control features are still facing enormous challenges. Herein, the star family, organic–inorganic hybrid perovskites, embraces a new member, [C5H14N]2·[CdCl4] (1), which simultaneously displays rapid dielectric and fluorescence response under the stimulus of heat. Specifically, 1 exhibits a phase transition below room temperature (Tc = 239 K, and ΔT < 8 K) including a thermal anomaly, dielectric transition, and symmetry breaking. And the Mn-doped crystal could exhibit temperature-dependent red luminescence under UV excitation with a high signal-to-noise ratio of 3. Besides, the dielectric/fluorescent dual response triggered by heat exhibits a rapid response and high fatigue resistance. This finding will be a further step to the practical application of stimulus-responsive materials based on two-dimensional perovskites in smart electronic devices.

A semiconductor material [(CH2)3NH2S]2BiCl5 (1) exhibits dielectric switching and Pd uptake functions. The thioether group in 1 provides an opportunity for Pd uptake. After 1 adsorbs Pd, the dielectric switching disappears, so that Pd adsorption can be monitored by dielectric measurements. Moreover, the material becomes an insulator after adsorbing Pd.

The research on multifunctional response materials has been rapidly increasing with the boom of the Information Age, due to their attractive applications in various smart devices. However, the design and regulation of multifunctional response materials by structural adjustments are still facing enormous challenges. Here, we report two organic–inorganic hybrids (IPTMA)2CdBr4 and (IPTMA)2MnBr4 (IPTMA = isopropyl-trimethylammonium), which exhibit excellent switchable dielectric response upon exposure to a thermal stimulus. It is considered that the changes in the metal skeletons by replacing Cd with Mn result in different functional characteristics for the two hybrids. Moreover, (IPTMA)2MnBr4 shows highly efficient green-light emission with a high quantum yield of 52.6%, and further shows another, optical response, which makes it a potential candidate for application in smart response devices. This work would offer a new perspective on the effective design of multifunctional response materials.

Multifunctional materials enable the integration of multiple physical signals in a single device for seamless integration, offering new opportunities in areas such as modern smart devices. For the needs of flexible devices, molecular functional materials are highly preferred due to their structural tunability, environmental friendliness and easy film formation. However, designing such multifunctional materials suitable for thin film devices has always been a huge challenge, especially semiconducting switchable dielectrics. Considering the unique structural properties and mechanical flexibility of plastic crystals, we have successfully designed an excellent multifunctional material, (N,N-dimethylpiperidinium)3Bi2Cl9, which shows outstanding dielectric switching and semiconducting behavior comparable to ZnO. The plastic phase transition below room temperature and multiaxial characteristics caused by structural variation give its thin film preferred structural flexibility, good uniformity and stability. These attributes make it a potential candidate in flexible multifunctional devices, realizing the high-performance integration of semiconducting and switchable properties.

Two-dimensional organic-inorganic hybrid perovskites (OIHPs) have gained attention as a result of their flexibility and adjustability of the structure. However, the large band gap of two-dimensional perovskites limits their application in the photoelectric field. In the present work, we report a two-dimensional organic-inorganic hybrid compound of (C

Organic–inorganic hybrid molecular ferroelastics have gained widespread attention as a promising candidate for data storage, sensor, and mechanical switch applications. However, it remains a great ...

Blue-light hazard in display will become a more serious problem because the wearable period is coming. Visual injury caused by the short wavelength is always the biggest challenge in red/green/blue ones. Therefore, the 470–475 nm is the most needed wavelength range to balance the visual injury and display effects. In addition, the combination of suitable wavelength, flexibility, and optic–electric coexistence has triggered a huge challenge in the wearable period to explore new blue-light materials. Under this epochal premise, lead-free blue light was introduced to form a dual photoelectric dielectric/blue-light switching flexible film/bulk crystal [Habf]2[ZnCl4]·2H2O (1) (Habf = p-ammonium benzene formamide), which will be a new breakthrough in photoelectric wearable devices. The coexistence of dielectric relaxation and high quantum yield in the most ideal emission wavelength facilitates the exploration of blue-light materials with low hazard, optical–electric response, and wearable characteristics in dis...

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]2PbCl4 as a high-performance ferroelectric semiconductor. The failures in the nonferroelectric [4-fluorobenzylammonium]2PbCl4 and [3-fluorobenzylammonium]2PbCl4 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.

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 =2.4 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.

With regard to the artificial molecular motor that was recognized with the 2016 Nobel Prize, this success proves the great scientific significance of rotary motor-type motion at the molecular level, which has been expected to play an invaluable role in the development of electronic information molecular materials. However, designing electronic information-critical high-temperature molecular motors has always been a huge challenge. Since we discovered [(CH3)3NCH2Cl]MnCl3, this cation rotation pattern with a motor-type motion structure has continued to attract our attention. Considering a strategy that combines molecular machines with dielectric theory, (N,N-dimethylpiperidinium)CdCl3, the new dielectric molecular motor material that exhibits superior physical properties, could be considered to be an excellent dielectric switch based on its electric field and temperature. Crystal structure analyses reveal that the reversible phase transition is mainly induced by the unusual chair-to-rotator motion of cation...

A flexible strategy for piezoelectrics Piezoelectric materials produce charge when they are deformed, making them ideal for various types of sensors. However, virtually all piezoelectric materials are ceramics, which are far from ideal for applications requiring flexible sensors. Liao et al. now describe a molecular material with piezoelectric properties comparable to the industry-standard ceramic lead zirconate titanate. The exceptional properties come from finding a molecular solid-solution series that allows for compositional optimization of the piezoelectric properties. Science , this issue p. 1206

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 ( Tc). Here, taking advantage of fluorine substitution on the reported molecular ferroelectric, (pyrrolidinium)MnCl3, we present enantiomeric perovskite ferroelectrics, namely, ( R) - and ( S) -3-(fluoropyrrolidinium)MnCl3. 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 Tc gets successfully increased from 295 K in (pyrrolidinium)MnCl3 to 333 K in these two homochiral compounds. Such a dramatic enhancement of 38 K signifies an important step toward designing high- Tc 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.

Sensors and memory switches promise to optimize the extent of, and access to, switchable dielectric materials. Multiaxial time-delayed dielectric switches holding extraordinary thermal hysteresis exhibit extensive potential in delay sensing and time-delayed triggering devices. Nonetheless, efficient evoking is still scarce. Since [(CH3)3NCH2Cl]MnCl31 was discovered by us, this cation rotation pattern with motor-type motion structure has further attracted our attention. Here, organic ionic plastic crystal (OIPC) [trimethylallyl ammonium]3[Bi2Cl9] [(TMAA)3-Bi2Cl9], a high-temperature multiaxial precision time-delayed dielectric switch crystal triggered by linear/propeller/ball three-form motion, mainly stems from the order–disorder transitions of [TMAA]+ cations, which are evidenced by heat anomalies of the temperature-dependent dielectric and differential scanning calorimetry (DSC) measurements, and the variable-temperature powder X-ray diffractometry (PXRD). The long time needed for a molecule to transition from rotational motion to a static condition can be ascribed to the exceptional linear-propeller-global ball-like motion, inducing the large thermal hysteresis. Intriguingly, the motion-stationary mode is reversible, that is to say, the thermal hysteresis temperature holds constant in each time, which is highly conducive to the precision time-delayed sensing. More importantly, our work will prompt the generation and evolution of novel delay sensors and switches, which makes it a new upsurge in high-performance dielectric response materials with multiaxial natures.

Three new organic molecule-based compounds, ethyl-trimethyl-phosphonium picrate (1, [ETtmp][picrate]), hydroxymethyl-trimethyl-phosphonium picrate (2, [HMtmp][picrate]), and cyclopentyl-trimethyl-phosphonium picrate (3, [CPtmp][picrate]), have been corroborated as high-temperature phase transition materials possessing switchable dielectric behaviors. Compounds 1, 2 and 3 undergo dielectric anomalies which could be tuned in two pronounced dielectric states and switched by reversible phase transitions at 320.8 K, 393.9 K and 398.1 K, respectively. For compounds 1, 2 and 3, not only the phase transition temperatures but also the magnitudes of the dielectric anomalies presented variations by regulating the guest cations. The respective dielectric constants in the high dielectric states are 1.6, 2.7 and 3.6 times those in the low dielectric states for compounds 1, 2 and 3. And considering the big entropy changes (ΔS) in the three title compounds, we predicted the sensitivities of the phase transition temperatures (Tc) to the applied pressure. And the estimated barocaloric coefficients (δTc/δP) in the three title compounds indicate that they potentially perform barocaloric effects of interest for cooling applications under adequate pressure.

An organic-inorganic perovskite compound [(CH3)4P][Cd(SCN)3] (1) and its fluorine-substituted product [(CH3)3PCH2F][Cd(SCN)3] (2) exhibit ferroelastic phase transitions above room temperature. The very close van der Waals radii of H and F atoms ensure isomorphism of the crystal structures. However, the higher phase transition temperature, stronger ferroelastic spontaneous strain value and dielectric properties of 2 can possibly be explained by differences in the electronegativity between F and H atoms.

Phase transition materials are a class of smart materials with special optoelectronic properties. In particular, high symmetry has proven to be the most advantageous feature for thin film devices. However, phase transition design, particularly with high symmetry, is a huge challenge. Herein, based on the advanced molecule reported by us, [(CH3)3N(CH2)2Cl]2[ZnCl4] (1) was verified to be a phase transition dielectric crystal with an infrequent large leap symmetry breaking from P21/c to I41/a at 333 K. The dielectric value exhibited a remarkable step-like enlargement around TC, suggesting a standard and visual low-high interchange of dielectric switching. The existence of dielectric switching properties triggered by a thermal stimulus is intrinsically induced by the anionic and cationic order–disorder motion. It creates a little anisotropy along all axial directions in numerical values and cardinal numbers, which is very beneficial for the cultivation of large-size crystals and the fabrication of corresponding devices.

Organic-inorganic hybrid perovskites are currently an active research topic in the field of energy and next-generation electronics. Their selectable organic and inorganic components provide infinite possibilities for designing functional materials with multiple applications. Herein, we present a new one-dimensional BaNiO3-like organic-inorganic hybrid perovskite (thiazolidinium)CdBr3 (1), which displays a phase transition at 263 K and a switchable second harmonic generation (SHG) response. Intriguingly, 1 shows a pyroelectric coefficient pe of ∼0.6 μC·cm-2·K-1 and a piezoelectric output voltage of ∼2.0 V for our fabricated piezoelectric generation device, indicating its great potential for pyroelectric sensors, self-powered low-voltage electronic devices, and energy harvesters. Moreover, the presence of a specific thioether donor enables 1 to appropriately adsorb Pd(II) ions, which can be monitored by the corresponding change in phase transition behavior, SHG signal, and pyroelectric response. This work provides a new insight to develop new multifunctional materials, demonstrating the feasibility of utilizing organic-inorganic hybrid perovskites to realize future self-powered low-voltage devices and energy harvesters.

Molecular-based ionic co-crystals, which have the merits of low-cost/easy fabrication processes and flexible structure and functionality, have already exhibited tremendous potential in molecular memory switches and other electric devices. However, dipole (ON/OFF switching) triggering is a huge challenge. Here, we introduce a pendulum-like dynamic strategy to induce the order-disorder transition of a co-crystal [C5 H7 N3 Cl]3 [Sb2 Br9 ] (compound 1). Here, the anion and cation act as a stator and a pendulum-like rotor (the source of the dielectric switch), respectively. The temperature-dependent dielectric and differential scanning calorimetry (DSC) analyses reveal that 1 undergoes a reversible phase transition, which stems from the order-disorder transition of the cations. The thermal ON/OFF switchable motions make 1 a promising candidate to promote the development of bulk crystals as artificial intelligent dielectric materials. In addition, the pendulum-like molecular dynamics and distinct arrangements of two coexisting ions with a notable offset effect promotes/hinders dipolar reorientation after dielectric transition and provides a rarely observed but fairly useful and feasible strategy for understanding and modulating the dipole motion in crystalline electrically polarizable materials.

The perovskite structure is rich in ferroelectricity. In contrast, ferroelectric antiperovskites have been scarcely confirmed experimentally since the discovery of M3 AB-type antiperovskites in the 1930s. Ferroelectricity is now revealed in an organic-inorganic hybrid X3 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.

Due to having excellent properties of sensitive switchable physical and/or chemical response, simple preparation, and environmentally friendly processing, bistable switches (electric switching between “on” and “off” bistable states) have gradually developed into an ideal class of highly smart materials. However, most of them contain metals, especially heavy metals, which are highly toxic to the environment, and metal-free switch materials are rarely reported. Based on this issue, we successfully designed and synthesized organic ion crystals and realized thermal dielectric switching characteristics. Differential scanning calorimetry and dielectric measurements show that the large-size crystal (F-TEDA)(BF4)2 (1) can be regarded as an sensitive dielectric bistable switching between high (switch on) and low (switch off) dielectric states. Variable-temperature single crystal structure reveals one-half of the BF4– anions in the crystal undergoes order–disorder transition around 200 K, similar to the transition ...

It is known that perovskites with the general chemical formula of ABX3 (A, B = cations, X = anion) have been intensively studied over the last half century because of their diverse functional properties, such as ferroelectricity in BaTiO3, piezoelectricity in PZT (lead zirconate titanate), and recently developed photovoltaic properties in CH3NH3PbI3. However, rather less attention has been paid to their “inverse” analogs, antiperovskites, which have a chemical formula X3BA, where A and B are anions and X is a cation. Although most of important ferroelectrics are perovskites, no antiperovskite ferroelectrics have been found since the discovery of antiperovskites in 1930. Here, for the first time, we report a X3BA antiperovskite ferroelectric [(CH3)3NH]3(MnBr3)(MnBr4) (where (CH3)3NH is X, MnBr3 is B, and MnBr4 is A), which shows outstanding ferroelectricity with a significantly high phase transition temperature of 458 K as well as fascinating photoluminescence properties with two intense emissions. This fi...

Though dominating most of the practical applications, inorganic ferroelectric thin films usually suffer from the high processing temperatures, the substrate limitation, and the complicated fabrication techniques that are high-cost, energy-intensive, and time-consuming. By contrast, molecular ferroelectrics offer more opportunities for the next-generation flexible and wearable devices due to their inherent flexibility, tunability, environmental-friendliness, and easy processability. However, most of the discovered molecular ferroelectrics are uniaxial, one major obstacle for improving the thin-film performance and expanding the application potential. In this Perspective, we overview the recent advances on multiaxial molecular ferroelectric thin films, which is a solution to this issue. We describe the strategies for screening multiaxial molecular ferroelectrics and characterizations of the thin films, and highlight their advantages and future applications. Upon rational and precise design as well as optimizing ferroelectric performance, the family of multiaxial molecular ferroelectric thin films surely will get booming in the near future and inject vigor into the century-old ferroelectric field.

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.

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.

With the flourishing development of (CH3NH3)PbI3, 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 [H2dabco]RbCl3 adopts a nonpolar crystal structure without ferroelectricity. Within the larger RbI3 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 d...