Da-Wei Fu

Supramolecular bola-like ferroelectric: 4-methoxyanilinium tetrafluoroborate-18-crown-6.

Molecular motion is one of the structural foundations for the development of functional molecular materials such as artificial motors and molecular ferroelectrics. Herein, we show that pendulum-like motion of the terminal group of a molecule causes a ferroelectric phase transition. Complex 4-methoxyanilinium tetrafluoroborate-18-crown-6 ([C(7)H(10)NO(18-crown-6)](+)[BF(4)](-), 1) shows a second-order ferroelectric phase transition at 127 K, together with an abrupt dielectric anomaly, Debye-type relaxation behavior, and the symmetry breaking confirmed by temperature dependence of second harmonic generation effect. The origin of the polarization is due to the order-disorder transition of the pendulum-like motions of the terminal para-methyl group of the 4-methoxyanilinium guest cation; that is, the freezing of pendulum motion at low temperature forces significant orientational motions of the guest molecules and thus induces the formation of the ferroelectric phase. The supramolecular bola-like ferroelectric is distinct from the precedent ferroelectrics and will open a new avenue for the design of polar functional materials.

Diisopropylammonium Chloride: A Ferroelectric Organic Salt with a High Phase Transition Temperature and Practical Utilization Level of Spontaneous Polarization

A simple organic salt, diisopropylammonium chloride, shows the highest ferroelectric phase transition temperature among molecule-based ferroelectrics with a large spontaneous polarization, making it a candidate for practical technological applications.

Hydrogen-Bonded Ferroelectrics Based on Metal−Organic Coordination

Metal-organic coordination (MOC)-type ferroelectrics, cobalt(II) (R)-2-methylpiperazine (MPPA) trichloride [Co(II)Cl(3)(H-MPPA)], was constructed through hydrogen bonds. It is a good ferroelectric candidate with a P(s) = 6.8 microC.cm(-2) as high as almost twice that of triglycine sulfate (P(s) = 3.5 microC.cm(-2)) and significantly larger than that of KH(2)PO(4) at the low-temperature ferroelectric phase Fdd2. [Co(II)Cl(3)(H-MPPA)] is the first example of ferroelectric MOC that can really reach the spontaneous polarization status and opens up a new avenue to explore novel MOC-based ferroelectrics.

Highly Efficient Red-Light Emission in An Organic–Inorganic Hybrid Ferroelectric: (Pyrrolidinium)MnCl3

Luminescence of ferroelectric materials is one important property for technological applications, such as low-energy electron excitation. However, the vast majority of doped inorganic ferroelectric materials have low luminescent efficiency. The past decade has envisaged much progress in the design of both ferroelectric and luminescent organic-inorganic hybrid complexes for optoelectronic applications. The combination of ferroelectricity and luminescence within organic-inorganic hybrids would lead to a new type of luminescent ferroelectric multifunctional materials. We herein report a hybrid molecular ferroelectric, (pyrrolidinium)MnCl3, which exhibits excellent ferroelectricity with a saturation polarization of 5.5 μC/cm(2) as well as intense red luminescence with high quantum yield of 56% under a UV excitation. This finding may extend the application of organic-inorganic hybrid compounds to the field of ferroelectric luminescence and/or multifunctional devices.

An organic-inorganic perovskite ferroelectric with large piezoelectric response

Finding a more flexible mechanical sensor Piezoelectric materials allow conversion between electricity and mechanical stresses. The most efficient piezoelectric materials are ceramics such as BaTiO3 or PbZrO3, which are also extremely stiff. You et al. identified an organic perovskite structured piezoelectric material that is far more pliable yet has a piezoelectric response similar to that of traditional ceramics. This material may be a better option to use as a mechanical sensor for flexible devices, soft robotics, biomedical devices, and other micromechanical applications that benefit from a less stiff piezoelectric material. Science, this issue p. 306 Trimethylchloromethyl ammonium trichloromanganese(II) may be a flexible material competitive for piezoelectric applications. Molecular piezoelectrics are highly desirable for their easy and environment-friendly processing, light weight, low processing temperature, and mechanical flexibility. However, although 136 years have passed since the discovery in 1880 of the piezoelectric effect, molecular piezoelectrics with a piezoelectric coefficient d33 comparable with piezoceramics such as barium titanate (BTO; ~190 picocoulombs per newton) have not been found. We show that trimethylchloromethyl ammonium trichloromanganese(II), an organic-inorganic perovskite ferroelectric crystal processed from aqueous solution, has a large d33 of 185 picocoulombs per newton and a high phase-transition temperature of 406 kelvin (K) (16 K above that of BTO). This makes it a competitive candidate for medical, micromechanical, and biomechanical applications.

High-Temperature Ferroelectricity and Photoluminescence in a Hybrid Organic–Inorganic Compound: (3-Pyrrolinium)MnCl3

Coupling of ferroelectricity and optical properties has become an interesting aspect of material research. The switchable spontaneous polarization in ferroelectrics provides an alternative way to manipulate the light-matter interaction. The recent observation of strong photoluminescence emission in ferroelectric hybrid organic-inorganic compounds, (pyrrolidinium)MnX3 (X = Cl or Br), is an attractive approach to high efficiency luminescence with the advantages of ferroelectricity. However, (pyrrolidinium)MnX3 only displays ferroelectricity near or below room temperature, which limits its future applications in optoelectronics and multifunctional devices. Here, we rationally designed and synthesized high-temperature luminescent ferroelectric materials. The new hybrid compound (3-pyrrolinium)MnCl3 has a very high Curie temperature, Tc = 376 K, large spontaneous electronic polarization of 6.2 μC/cm(2), and high fatigue resistance, as well as high emission efficiency of 28%. This finding is a further step to the practical use of ferroelectric luminescence based on organic-inorganic compounds.

An Order–Disorder Ferroelectric Host–Guest Inclusion Compound

The host-guest complex [(DIPA)([18]crown-6)](ClO4) (1; DIPA=2,6-diisopropylanilinium) was constructed and found to undergo a sequence of phase transitions (Ibam-Pbcn-Pna21) at T1=278 K and T2=132 K, respectively. Systematic characterizations, such as differential scanning calorimetry, heat capacity, temperature-dependent dielectric constant, and P-E hysteresis loop, reveal that the centrosymmetric-to-polar phase transition at T2 is a paraelectric-to-ferroelectric transition. The symmetry breaking was also confirmed by temperature-dependent second-harmonic generation effect and X-ray powder diffraction. The ferroelectric mechanism is attributable to the linear motion of the perchlorate counterions accompanied by the order-disorder transition of the [18]crown-6 molecules and the anions.

Switchable Dielectric, Piezoelectric, and Second‐Harmonic Generation Bistability in a New Improper Ferroelectric above Room Temperature

Imidazolium periodate (IPI) is found to be an improper ferroelectric. It shows bistable properties simultaneously in three channels of dielectricity, piezoelectricity, and second-harmonic generation within the temperature window 300-310 K.

An Above-Room-Temperature Ferroelectric Organo–Metal Halide Perovskite: (3-Pyrrolinium)(CdCl3)†

Hybrid organo-metal halide perovskite materials, such as CH3NH3PbI3, have been shown to be some of the most competitive candidates for absorber materials in photovoltaic (PV) applications. However, their potential has not been completely developed, because a photovoltaic effect with an anomalously large voltage can be achieved only in a ferroelectric phase, while these materials are probably ferroelectric only at temperatures below 180 K. A new hexagonal stacking perovskite-type complex (3-pyrrolinium)(CdCl3) exhibits above-room-temperature ferroelectricity with a Curie temperature T(c)=316 K and a spontaneous polarization P(s)=5.1 μC cm(-2). The material also exhibits antiparallel 180° domains which are related to the anomalous photovoltaic effect. The open-circuit photovoltage for a 1 mm-thick bulky crystal reaches 32 V. This finding could provide a new approach to develop solar cells based on organo-metal halide perovskites in photovoltaic research.

The First Organic–Inorganic Hybrid Luminescent Multiferroic: (Pyrrolidinium)MnBr3

A hybrid organic-inorganic compound, (pyrrolidinium)MnBr3 , distinguished from rare earth (RE)-doped inorganic perovskites, is discovered as a new member of the ferroelectrics family, having excellent luminescent properties and relatively large spontaneous polarization of 6 μC cm(-2) , as well as a weak ferromagnetism at about 2.4 K. With a quantum yield of >28% and emission lifetime >0.1 ms, such multiferroic photoluminescence is a suitable candidate for future applications in luminescence materials, photovoltaics, and magneto-optoelectronic devices.