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Organic single-component ferroelectrics with low molecular mass have drawn great attention for applications in organic electronics. However, the discovery of high-Tc single-component organic ferroelectrics has been very scarce. Herein, we report a pair of homochiral single-component organic ferroelectrics (R)-10-camphorsulfonylimine and (S)-10-camphorsulfonylimine under the guidance of ferroelectric chiral chemistry. They crystallize in chiral-polar space group P21, and their mirror image relations have been identified by vibrational circular dichroism spectra. They both exhibit 422F2 multiaxial ferroelectricity with Tc as high as 429 K. Besides, they possess superior acoustic impedance characteristic with the value of 2.45×106 kg·s-1·m-2, lower than that of PVDF. To our knowledge, enantiomeric (R and S)-10-camphorsulfonylimine show the highest Tc among the known organic single-component ferroelectrics and the low acoustic impedance well matching with the bodily tissues. This work promotes the development of high-performance organic single-component ferroelectrics and is of great inspiration to explore the applications in next-generation flexible smart devices.

Since the discovery of the first ferroelectric Rochelle salt, most ferroelectrics have been investigated showing thermally triggered symmetry-breaking phase transition. Although photochromism arising from geometrical isomerization has been reported earlier in 1867, such photoswitchable ferroelectric crystals have scarcely been developed to date. Herein, we report that salicylideneaniline is a photochromic ferroelectric crystal. Upon photoirradiation, the dielectric constant shows obvious switching between high and low dielectric states, and more importantly, the ferroelectric polarization demonstrates quickly and reversibly switching. This work opens the gate of developing photoswitchable ferroelectrics, which holds great potential for applications in optically controlled smart devices.

Since the discovery of TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl) in 1973, organic radical ferroics attracted widespread interest among the scientific community. However, the relatively low Curie temperature of 287 K and melting point of 311 K severely hinder its application potential. Despite extensive interest, high-temperature radical ferroics have not been found to date. Here, taking advantage of chemical design theory and supramolecular radical chemistry, we successfully designed two high-temperature organic supramolecular radical ferroics [(NH3-TEMPO)([18]crown-6)](ReO4) (1) and [(NH3-TEMPO)([18]crown-6)](ClO4) (2), which can retain the ferroelectricity up to 413 K and 450 K, respectively. To our knowledge, they are both the first supramolecular radical ferroics and unprecedented high-temperature radical ferroics, where the supramolecular component plays a vital role in the stabilization of radical and extending working temperature window. Additionally, both of them can also present the paramagnetism and non-interacting spin moments, as well as excellent piezoelectric and electrostrictive behaviors comparable to that of LiNbO3. This work provides an efficient design strategy for enriching the family of high-temperature radical ferroics, and should inspire further exploration of multi-functional organic ferroics.

Multiferroic materials have attracted great interest because of their underlying new science and promising applications in data storage and mutual control devices. However, they are still very rare and highly imperative to be developed. Here, we report an organic–inorganic hybrid perovskite trimethylchloromethylammonium chromium chloride (TMCM–CrCl3), showing the coexistence of magnetic and electric orderings. It displays a paraelectric–ferroelectric phase transition at 397 K with an Aizu notation of 6/mFm, and spin-canted antiferromagnetic ordering with a Néel temperature of 4.8 K. The ferroelectricity originates from the orientational ordering of TMCM cations, and the magnetism is from the [CrCl3]− framework. Remarkably, TMCM–CrCl3 is the first experimentally confirmed divalent Cr2+-based multiferroic material as far as we know. A new category of hybrid multiferroic materials is pointed out in this work, and more Cr2+-based multiferroic materials will be expectedly developed in the future., An organic–inorganic hybrid perovskite Trimethylchloromethylammonium chromium(ii) chloride (TMCM–CrCl3) can simultaneously show excellent ferroelectricity and antiferromagnetism, which is the first experimentally confirmed Cr2+-based multiferroic material.

Chiral perovskites have emerged as a significant class of materials showing promising optoelectronic and spintronic applications. Reports of chiral perovskite ferroelectrics, however, have been scarce. In this work, we have successfully synthesized homochiral lead-iodide perovskite ferroelectrics [(R)-N-(1-phenylethyl)ethane-1,2-diaminium]PbI4 and [(S)-N-(1-phenylethyl)ethane-1,2-diaminium]PbI4 by the chemical design of introducing a methyl group into the organic cation of the parent (N-benzylethane-1,2-diaminium)PbI4. Vibrational circular dichroism spectra identify the chiral mirroring relationship. They both undergo 222F2 type paraelectric-ferroelectric behavior at around 378 K coupled with clear ferroelastic domains "ON/OFF" switching. Besides, they exhibit an evident thermochromism with color change from orange-yellow to orange-red. To our knowledge, the discovery of integrated ferroelectricity, ferroelasticity and reversible thermochromism in chiral perovskites is unprecedented. This finding offers a resultful path to design chiral perovskite ferroelectrics and is of great inspiration to the discovery of multifunctional perovskite materials.

The optical control of polarization switching is attracting tremendous interest because photoirradiation stands out as a nondestructive, noncontact, and remote-control means beyond an electric or strain field. The current research mainly uses various photoexcited electronic effects to achieve the photocontrol polarization, such as a light-driven flexoelectric effect and a photovoltaic effect. However, since photochromism was discovered in 1867, the structural phase transition caused by photoisomerization has never been associated with ferroelectricity. Here, we successfully synthesized an organic photochromic ferroelectric with polar space group Pna21, 3,4,5-trifluoro-N-(3,5-di-tert-butylsalicylidene)aniline, whose color can change between yellow and orange via laser illumination. Its dielectric permittivity and spontaneous polarization can be switched reversibly with a photoinduced phase transition triggered by structural photoisomerization between the enol form and the trans-keto form. To our knowledge, this is the first photoswitchable ferroelectric crystal to achieve polarization switching through a structural phase transition triggered by photoisomerization. This finding paves the way toward photocontrol of smart materials and biomechanical applications in the future.

Topological defects such as vortices in ferroelectric materials are attracting tremendous interest because of their splendid possibilities for unique physical phenomena and potential applications in nanoelectronic devices. However, reports of the vortex structure have been scarce in organic ferroelectrics, which are highly desirable for their mechanical flexibility, easy and environment-friendly processing, and low acoustical impedance. Here, we successfully observed the robust triangular domains in a single-component organic ferroelectric, 2-(hydroxymethyl)-2-nitro-1,3-propanediol (1), six of which can form a 6-fold vertex domain structure. To our knowledge, it is the first time that such an intriguing topological vortex gets experimentally confirmed in ferroelectrics. Moreover, the symmetry change of 1 with an Aizu notation of m3mF1 leads to the most 48 crystallographically equivalent polarization directions among all ferroelectrics. With those benefits and excellent piezoelectric properties, compound 1 shows great potential as a reconfigurable electronic element or a mechanical sensor for soft robotics, flexible and wearable devices, and biomachines.

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.

A high transition temperature (Tc ) is essential for the practical application of ferroelectrics as electronic devices under extreme thermal conditions in the aerospace, automotive, and energy industries. In recent decades, the isotope effect and strain engineering are found to effectively modulate Tc ; however, these strategies are limited to certain systems. Developing simple, universal, and practical methods to improve Tc has become an imminent challenge for expanding the applications of ferroelectrics. Here, by adopting a molecular design strategy involving H/F substitution on an organic-inorganic hybrid perovskite (1-azabicyclo[2.2.1]heptane)CdCl3 at a Tc of 190 K, the successful synthesis of a multiaxial, ferroelectric hybrid perovskite (4-fluoro-1-azabicyclo[2.2.1]heptane)CdCl3 is reported, which demonstrates a large spontaneous polarization of 11.2 µC cm-2 (greater than that of polyvinylidene difluoride) and a Tc of 419 K (greater than that of BaTiO3 ). This temperature enhancement (229 K) is the largest reported for molecular ferroelectrics, far exceeding the reported enhancements induced by the isotope effect and other techniques. This pioneering technique provides an effective and universal method for improving Tc in ferroelectrics and represents an important step toward the development of high-performance ferroelectric technology.