A Temperatural Semi-Memorized Phase Transition in a 1D Organic-Inorganic Hybrid Material of Sb|||-Based [(CH2)3NH2S]2SbCl5

Tunability of Photovoltaic Functions via Halogen Substitution [(Ade)2 CdX4](X = Cl, Br): A Class of Three-Dimensional Organic-Inorganic Hybrid Materials

Two new three-dimensional organic-inorganic hybrid crystalline materials, [(Ade)2 CdCl4] (1) and [(Ade)2 CdBr4] (2), were obtained by the slow evaporation of adenine (Ade) and cadmium chloride in aqueous solution at room temperature with hydrochloric acid and hydrobromic acid used as halogen sources. The structural, thermal, optical, and electrical properties were characterized by single-crystal X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, variable-temperature-variable-frequency dielectric constant analysis, and electrochemical tests. With increasing the substitution of Cl by Br, the composition of the material changed and the space group shifted from P-1 to P21/m, with a significant blue-shift in the fluorescence emission. Changing the temperature induced the deformation of the three-dimensional framework structure formed by hydrogen bonding interactions, leading to dielectric anomalies. Cyclic voltammetry tests showed the good reversibility of the electrolysis process. The structural diversity of the complexes was realized by modulating the halogen composition, and a new method for designing novel organic-inorganic hybrids with controllable photoelectric functionality was proposed.

High-Temperature Ferroelasticity and Photoluminescence in a 2D Monolayer Perovskite Compound: (C5NH8Br)2PbBr4

Hybrid organic-inorganic perovskites (HOIPs) have attracted much attention due to their excellent properties and easy synthesis. As far as we know, most documented ferroelastics mainly focus on the 3D (three-dimensional) perovskites, the 2D monolayer perovskite ferroelastics are rarely reported before. In this work, we synthesized a 2D lead-based perovskite (C₅NH₁₃Br)₂PbBr₄ (1) (C₅NH₁₃Br = 5-bromoamylamine cation) by introducing flexible chain organic cations. The evolution of ferroelastic domains observed by a polarized light microscope confirms that compound 1 undergoes a ferroelastic phase transition at 392/384 K. In addition, its direct band gap is 2.877 eV. Interestingly, the material emits an attractive blue light (quantum yield 5.06%) under UV light. Three structural descriptors are introduced to quantitatively analyze the relationship between structural distortion and the shape of emission peak. This work provides a way to design multifunctional perovskite-type materials.

Unusual symmetry breaking in high-temperature enantiomeric ferroelectrics with large spontaneous polarization

Chiral organic-inorganic hybrid perovskites have gained extensive research interest due to their combination of chirality and the excellent optical, electrical and spin properties of perovskite materials, especially in two-dimensional hybrid perovskites. Herein, we report two-dimensional organic-inorganic perovskite enantiomeric ferroelectric [(R)-β-MPA]₂CdCl₄ (1) and [(S)-β-MPA]₂CdCl₄ (2) (MPA⁺ =methylphenethylammonium). Their mirror relationships are verified by both circular dichroism (CD) and crystal structures. At the same time, the two exhibit very similar ferroelectricity and related properties, including high Curie temperature (343 K), large spontaneous polarization (4.65 μC cm^-2), and low coercive force field (13 kV cm^-1). Unusually, at room temperature the crystal phase is monoclinic with the space group C2 and above the phase transition temperature it is triclinic with the space group P1, which means that the symmetry decreases with the increase of temperature. In addition, it exhibits a flexible switchable SHG response, while [(R)-β-MPA]₂CdCl₄ and [(S)-β-MPA]₂CdCl₄ have wide band gaps of 4.21 and 4.26 eV, respectively, mainly contributed by inorganic CdCl₆ octahedra. This discovery opens a new way for the construction of two-dimensional enantiomeric molecular ferroelectrics.

Unusual high-temperature host–guest inclusion compound-based ferroelectrics with nonlinear optical switching and large spontaneous polarization behaviours

Host–guest inclusion compound-based ferroelectrics [Hcta-(18-crown-6)]+[BF4]− (1) and [Hcta-(18-crown-6)]+[ClO4]− (2) with a high Curie temperature (Tc = 403/394 K) and large spontaneous polarization (Ps = 5.7/4.7 μC cm−2) are reported.

High-Temperature Phase Transition Containing Switchable Dielectric Behavior, Long Fluorescence Lifetime, and Distinct Photoluminescence Changes in a 2D Hybrid CuBr4 Perovskite

A novel organic-inorganic hybrid perovskite crystal, [ClC₆H₄(CH₂)₂NH₃]₂CuBr₄ (1), having experienced an invertible high-temperature phase transition near T_c (the Curie temperature T_c = 355 K), has been successfully synthesized. The phase-transition characteristics for compound 1 are thoroughly revealed by specific heat capacity (C_p), differential thermal analysis, and differential scanning calorimetry tests, possessing 16 K broad thermal hysteresis. Multiple-temperature powder X-ray diffraction analysis further proves the phase-transition behavior of compound 1. Moreover, compound 1 exhibits a significant steplike dielectric response near T_c, revealing that it can be deemed to be a promising dielectric switching material. The variable-temperature fluorescence experiments show distinct photoluminescence (PL) changes of compound 1. Further investigation and calculation disclose that the fluorescence lifetime of compound 1 can reach as long as 55.46 μs, indicating that it can be a potential PL material. All of these researches contribute a substitutable avenue in the design and construction of neoteric phase-transition compounds combining high Curie temperature and PL properties.

Semi-conductive, Switchable Dielectric and Photoluminescent Properties of Two High-Temperature Phase Transition Hybrids

Bistable switches (electrical switching between "ON" and "OFF" bistable states) have gradually developed into an ideal category of highly intelligent materials, due to their significant applications in optical technology, signal processors, data storage and other switchable media applications in the field of electrical devices. Here, we successfully designed and synthesized [(FC₆ H₄ C₂ H₄ NH₃ )₂ MCl₄ ]_n (FC₆ H₄ C₂ H₄ NH₃ ⁺ )=deprotonated 4-fluoro- phenethylamine; M=Cd (1), Mn (2)), which realized the coupling of thermo-dielectric switching characteristics, semi-conductor characteristics and photo-luminescent properties. DSC (differential scanning calorimetry) and dielectric measurements show that 1 is a sensitive dielectric bistable switch between the high dielectric (ON) and low dielectric (OFF) states. The temperature-variable single crystal structure shows that the both 1 and 2 undergo a high-temperature reversible phase transition around 383 K/380 K, which is caused by the order-disordered transformation of organic cations and the slight distortion of the inorganic framework. In particular, 1 shows outstanding switchable dielectric behavior and semiconducting properties. Further, 1 and 2 emit strong green and yellow luminescence at 527 and 595 nm, respectively.

A multifunctional molecular ferroelectric with chiral features, a high Curie temperature, large spontaneous polarization and photoluminescence: (C9H14N)2CdBr4

Low-dimensional chiral organic-inorganic hybrid metal halides have attracted a lot of attention in recent years due to their unique intrinsic properties, including having potential applications in optoelectronic and spintronic devices. However, low-dimensional chiral molecular ferroelectrics are very rare. In this paper, we report a novel zero-dimensional molecular ferroelectric (C9H14N)2CdBr4 (C9H14N+ = protonated 3-phenylpropylamine), which has obvious dielectric and thermal anomalies and shows a high Curie temperature at 395 K. It crystallizes in the P21 space group at room temperature, showing a strong CD signal, large spontaneous polarization (P s = 13.5 μC cm-2), and a clear ferroelectric domain. In addition, it also exhibits a flexible SHG response. The photoluminescence spectrum shows that 1 has broadband luminescence. At the same time, compound 1 has a wide band gap, which is mainly contributed to by the inorganic CdBr4 tetrahedron. The high tunability of low-dimensional chiral molecular ferroelectrics also opens up a way to explore multifunctional chiral materials.

Molecular Disorder Induces an Unusual Phase Transition in a Potential 2D Chiral Ferroelectric Perovskite

Two-dimensional hybrid halide perovskites with single chiral and ferroelectricity together with various structural phase transitions provide the possibility for more diverse functional properties. Here, we present a 2D chiral hybrid halide perovskite ferroelectric, [C₆ H₅ (CH₂ )₄ NH₃ ]₂ CdCl₄ (4PBA-CdCl₄ , 4PBA=4-phenylbutylamine) that experiences two continuous phase transitions from centrosymmetric triclinic P 1 ‾ to polar chiral monoclinic P2 and then to another centrosymmetric tetragonal P4/mmm with increasing temperature, accompanied by symmetry breaking, due to the prominent octahedral distortion and disorder transformation of organic 4PBA cations. In the polar chiral phase, 4PBA-CdCl₄ gives a significant CD signal and has a moderate ferroelectric polarization of 0.35 μC/cm² . In addition, 4PBA-CdCl₄ occupies a wide band gap of 4.376 eV that is chiefly contributed by the inorganic CdCl₆ octahedron. This finding offers an alternative pathway for designing new phase transitions and related physical properties in hybrid halide perovskites and other hybrid crystals.

Acentric Organic-Inorganic Hybrid Halide [N(CH3)4]2HgBr2I2 Featuring an Isolated [HgBr2I2]2- Tetrahedron and Second-Order Nonlinearity

A new hybrid compound [N(CH₃)₄]₂HgBr₂I₂, obtained by a hydrothermal reaction, crystallized in the noncentrosymmetric space group P2₁2₁2₁. Its structure contains an isolated asymmetric [HgBr₂I₂]^2- tetrahedron with net polarization, connected by hydrogen bonds to form pseudo-one-dimensional chain structures. Moreover, its optical band gap, nonlinear optical (NLO) property, fluorescence property, and thermal property were characterized in detail. A rare high-temperature phase transition was observed in the compound. In addition, theoretical calculations were performed to elaborate the relation between electronic state, band structure, and their nonlinear optical response. These results indicate that [N(CH₃)₄]₂HgBr₂I₂ is a new potential candidate for future photoelectronic applications in fluorescence and nonlinear optics.

Chiral Switchable Low-Dimensional Perovskite Ferroelectrics

Low-dimensional hybrid organic-inorganic perovskites (HOIPs) possess more localized electronic states and narrower conduction and valence bands to promote self-trapping of excitons and stronger exciton emission; therefore, they are widely used as building blocks for various applications in the fields of optoelectronics, photovoltaics, light-emitting diodes, luminescence, fluorescence, and so forth. Despite the past decades of intensive study, the discovered low-dimensional chiral HOIPs are rare as of the 1D chiral HOIP single crystals reported in 2003, as well as the low-dimensional chiral HOIP ferroelectrics are particularly scarce since the first chiral two-dimensional (2D) and/or one-dimensional (1D) HOIP ferroelectrics reported. Herein, two new low-dimensional HOIPs with the same conformational formula [R-MPA]₂CdCl₄ (R-MPA⁺ = (R)-(-)-1-methyl-3-phenylpropylamine) were successfully synthetized by means of regulating the stoichiometric proportion of R-MPA and CdCl₂ in two ways of 1:1 (1) and 2:1 (2). By combining single-crystal X-ray diffraction, circular dichroism (CD) spectroscopy, differential scanning calorimetry, temperature-dependent dielectric constant, temperature-dependent second-harmonic generation (SHG) effect, polarization-dependent SHG response, and P-E hysteresis loop, we reveal that 1 is a 1D nonchiral molecular ferroelectric and 2 is the first zero-dimensional (0D) chiral ferroelectric with distinct CD signals; meanwhile, 2 exhibits increased properties of high-T_c, large dielectric constant, SHG isotropy, and ferroelectricity than that of 1. These results not only shed light on the high tunability of the low-dimensional HOIP ferroelectrics but also open up an avenue to explore multifunctional chiral ferroelectrics.

Multifunctional rare earth molecular ferroelectrics with a piezoelectric response: ((nBu)4N)3[Ce(NO3)4(SCN)2]((CH3CH2CH2CH2)4N = tetrabutylammonium)

A new type of multipolar rare earth molecular ferroelectric: ((nBu)4N)3[Ce(NO3)4(SCN)2] (BuCH3CH2CH2CH2)4N), undergoes a high-temperature ferroelectric phase transition, possesses flexible switchable SHG effect, moderate spontaneous polarization and a narrow band gap.

Multisequential reversible phase transition materials with semiconducting and fluorescence properties: (C8H18BrN)2SnBr6

A novel organic–inorganic hybrid metal halide has synthesized, namely (C8H18BrN)2SnBr6 (1), which have excellent switchable dielectric properties, narrow band gap and broadband yellow fluorescence characteristics.

A chiral lead-free photoactive hybrid material with a narrow bandgap

A chiral lead-free hybrid of (C₅H₁₁N₃)SbI₅ was synthesized that exhibits a narrow bandgap, typical semiconducting behavior and notable photoresponse.