Ferroelectric Metal–Organic Frameworks

This review (over 380 references) summarizes metal–organic frameworks (MOFs), Materials Institute Lavoisier (MILs), iso-reticular metal–organic frameworks (IR-MOFs), porous coordination networks (PCNs), zeolitic metal–organic frameworks (ZMOFs) and porous coordination polymers (PCPs) with selected examples of their structures, concepts for linkers, syntheses, post-synthesis modifications, metal nanoparticle formations in MOFs, porosity and zeolitic behavior for applications in gas storage for hydrogen, carbon dioxide, methane and applications in conductivity, luminescence and catalysis.

MOFs, MILs and more: concepts, properties and applications for porous coordination networks (PCNs)

An insight into the analogies, state-of-the-art technologies, concepts, and prospects under the umbrella of perovskite materials (both inorganic-organic hybrid halide perovskites and ferroelectric perovskites) for future multifunctional energy conversion and storage devices is provided. Often, these are considered entirely different branches of research; however, considering them simultaneously and holistically can provide several new opportunities. Recent advancements have highlighted the potential of hybrid perovskites for high-efficiency solar cells. The intrinsic polar properties of these materials, including the potential for ferroelectricity, provide additional possibilities for simultaneously exploiting several energy conversion mechanisms such as the piezoelectric, pyroelectric, and thermoelectric effect and electrical energy storage. The presence of these phenomena can support the performance of perovskite solar cells. The energy conversion using these effects (piezo-, pyro-, and thermoelectric effect) can also be enhanced by a change in the light intensity. Thus, there lies a range of possibilities for tuning the structural, electronic, optical, and magnetic properties of perovskites to simultaneously harvest energy using more than one mechanism to realize an improved efficiency. This requires a basic understanding of concepts, mechanisms, corresponding material properties, and the underlying physics involved with these effects.

Mutual Insight on Ferroelectrics and Hybrid Halide Perovskites: A Platform for Future Multifunctional Energy Conversion.

2.4.2. Interpenetrated Ladders 711 2.4.3. Unusual Motifs of Ladders 713 2.4.4. Properties of Ladderlike Chains 713 2.5. Rotaxane Polymers 714 2.5.1. 1D Polyrotaxanes 714 2.5.2. 2D Polyrotaxanes 715 2.5.3. 3D Polyrotaxanes 716 2.5.4. Hydrogen-Bonded Polyrotaxanes 716 2.6. Ribbon/Tape Polymers 717 2.7. Metal Cluster As Building Blocks for 1D CP 718 2.7.1. Metal Carboxylate Clusters 718 2.7.2. Metal Halide Clusters 719 2.7.3. Metal Chalcogenide Clusters 720 2.7.4. Polyoxometalate Clusters 721 2.7.5. Single Molecular Magnets as Building Blocks 722

One-Dimensional Coordination Polymers: Complexity and Diversity in Structures, Properties, and Applications

The term nonlinear optics (NLO) was coined to describe the nonlinear relationship between dielectric polarization P and electric field E in optical media. NLO is a cornerstone of the emerging field of photonics, in which photons instead of electrons are used for signal transmission and processing. The vision of photonic signal transmission, processing, and storage has attracted a great deal of attention from both the engineering and the scientific communities because of its great impact in many of the existing and future information technologies. The first step toward realization of these revolutionary technologies is to develop tools to manipulate photons. For example, it is desirable to develop materials with the ability to alter the frequency of light, to amplify light signal, and to modulate light intensity or phase factors. NLO phenomena can be the key to achieving these important functions. One of the most common NLO behaviors is second-harmonic generation (SHG), in which a NLO material mediates the “adding-up” of two photons to form a new one with twice the frequency. The SHGphenomenonwas first demonstrated by Franken et al. in 1961. In their pioneering work, a laser beam with a wavelength of 694.2 nm was irradiated through a quartz crystal and an output ultraviolet radiation with a wavelength of 347.1 nm (double frequency) was detected. After this discovery, numerous nonlinear optical phenomena have been studied and a number of NLO-active materials have been developed. Second-harmonic generation can be quantitatively described by the second-order nonlinear optical susceptibility χ, a third-rank tensor with 27 components. The tensor elements are related to each other tomeet the requirements of both inherent and structural symmetries, which greatly reduces the number of independent components of the susceptibility tensor. Only crystals in noncentrosymmetric crystal classes can have nonvanishing χ. Moreover, for material crystallizing in the noncentrosymmetric 422, 622, and 432 crystal classes, the second-order NLO response might also vanish due to structural symmetry as well as Kleinman’s symmetry. Many inorganic compounds crystallize in noncentrosymmetric space groups and have been found to be SHG active. Some important examples are potassium dihydrogen phosphate (KDP = KH2PO4), lithium niobate (LiNbO3), and barium sodium niobate (Ba2NaNb5O15). 7 New inorganic compounds have been explored for NLO applications including but not limited to metal borates 12 and metal oxides. Recent structural studies on the inorganic systems have led to a better understanding of crystal growth/packing, paving the way for potentially manipulating their crystallization tendency to form noncentrosymmetric structures. Since the 1970s molecular NLO materials, including organic, organometallic, and inorganic complexes, have been of increasing interest to synthetic chemists. 19 The existing library of organic compounds was first screened, and the urea crystal has become a SHG standard because of its high SHG efficiency and usual availability. In a microscopic view, the second-order NLO susceptibility χ is related to the first hyperpolarizability β of a molecule. According to the classical two-level model, β is enhanced by a large transition moment and a large dipole moment difference between the ground and the charge transfer excited state. A donor acceptor type of molecule often possesses both a large transition moment and a large excited state dipole moment. As a result, most of the organic SHG chromophors belong to this category. However, most of the molecules with large β values also possess a large dipole moment, which induces formation of centrosymmetric assemblies of molecules due to dipole dipole interactions. One of the methods to avoid the centrosymmetric alignment of molecular dipoles is to trap them inside the channels of asymmetric porous host structures. 28 Other methods include formation of poled polymers in which the required asymmetry is imposed by the external electric field 35 and the Langmuir Blodgett (LB)

Rational synthesis of noncentrosymmetric metal-organic frameworks for second-order nonlinear optics.

H/F substituted perovskite compounds with above-room-temperature ferroelasticity: [(CH3)4P][Cd(SCN)3] and [(CH3)3PCH2F][Cd(SCN)3].

Two homochiral MOFs, (CBQ)CuI3(CN)3Br (1) and (CBC)CuI2.5(CN)2Br1.5 (2), were prepared by the solvothermal reaction of CuCN with N-4-cyanobenzyl quinidinium bromide (CBQ-Br) and N-4-cyanobenzylcinchonidinium bromide (CBC-Br). 1 and 2 are typical ferroelectric compounds while 1 may have dipolar relaxation ferroelectrics and a high dielectric constant (eo = 119.3).

Ferroelectric metal-organic coordination polymer with a high dielectric constant.

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.

Three-Dimensional Metal-Free Molecular Perovskite with a Thermally Induced Switchable Dielectric Response.

Molecular bistable switches (electrical switch “ON” and “OFF” bistable states) are a class of highly desirable intelligent materials due to their sensitive switchable physical and/or chemical response, easy and environmentally-friendly processing, light weight and mechanical flexibility. In particular, those switches with a rapid response are rarely reported. In this work, it is found that the supramolecular large-size crystal [H2DABCO][CdCl2(SO4)] (1) possesses a superior rapid switching performance for disordered oxygen atoms and swaying DABCO cations, displaying remarkably high sensitive and rapid dielectric bistable switching between high (switch ON) and low (switch OFF) dielectric states. This electrical switch reveals fatigue resistance and remarkable switching reversibility. Owing to obvious disordered oxygen atoms and swaying DABCO cations compared with the compound [H2DABCO][CdBr2(SO4)] (2), the permittivity of 1, jumping from 4 to ∼10, exhibits an almost vertical gradient in a relatively wide frequency range (responding time/temperature t = 0, which means that there is no responsive blind area), indicating a relatively more rapid electrical response compared with other reported molecular compounds. Therefore, compound 1 can be an excellent stimuli-responsive electrical switch, and its application in molecular/flexible electronic devices will have a profound significance.

Rapid dielectric bistable switching materials without a time/temperature responsive blind area in the linarite-like type molecular large-size single crystals

Da-Wei Fu

Papers

H/F substituted perovskite compounds with above-room-temperature ferroelasticity: [(CH3)4P][Cd(SCN)3] and [(CH3)3PCH2F][Cd(SCN)3].

Ferroelectric metal-organic coordination polymer with a high dielectric constant.

Three-Dimensional Metal-Free Molecular Perovskite with a Thermally Induced Switchable Dielectric Response.

Rapid dielectric bistable switching materials without a time/temperature responsive blind area in the linarite-like type molecular large-size single crystals

[(CH3)3PCH2OH][CdBr3] is a perovskite-type ferroelastic compound above room temperature.