Excellent Switchable Properties, Broad-Band Emission, Ferroelectricity, and High Tc in a Two-Dimensional Hybrid Perovskite: (4,4-DCA)2PbBr4 Exploited by H/F Substitution

Synthesis, the Reversible Isostructural Phase Transition, and the Dielectric Properties of a Functional Material Based on an Aminobenzimidazole-Iron Thiocyanate Complex

By introducing disordered molecules into a crystal structure, the motion of the disordered molecules easily induces the formation of multidimensional frameworks in functional crystal materials, allowing for structural phase transitions and the realization of various dielectric properties within a certain temperature range. Here, we prepared a novel ionic complex [C7H8N3]3[Fe(NCS)6]·H2O (1) between 2-aminobenzimidazole and ferric isothiocyanate from ferric chloride hexahydrate, ammonium thiocyanate, and 2-aminobenzimidazole using the evaporation of the solvent method. The main components, the single-crystal structure, and the thermal and dielectric properties of the complex were characterized using infrared spectroscopy, elemental analysis, single-crystal X-ray diffraction, powder XRD, thermogravimetric analysis, differential scanning calorimetry, variable-temperature and variable-frequency dielectric constant tests, etc. The analysis results indicated that compound 1 belongs to the P21/n space group. Within the crystal structure, the [Fe(NCS)6]3- anion formed a two-dimensional hydrogen-bonded network with the organic cation through S···S interactions and hydrogen bonding. The disorder-order motion of the anions and cations within the crystal and the deformation of the crystal frameworks lead to a significant reversible isostructural phase transition and multiaxial dielectric anomalies of compound 1 at approximately 240 K.

Second-Order Nonlinear Switching and Photoluminescence Properties of Cd-Based Hybrid Perovskite with High-Temperature Phase Transition

Recently, organic-inorganic hybrid perovskites exhibiting facile structural phase transitions have accumulated significant attention due to their switchable second-order nonlinear optical (NLO) properties, which hold significant promise for next-generation intelligent optoelectronic devices. In this study, we present a novel one-dimensional hexagonal hybrid perovskite, (4-methoxypiperidinium)CdCl3, which undergoes a reversible high-temperature structural phase transition at 389 K. Notably, (4-methoxypiperidinium)CdCl3 demonstrates switchable second-order NLO and dielectric properties, accompanied by symmetry breaking from the centrosymmetric Pnma to noncentrosymmetric Pna21 space group. Variable-temperature structure analyses reveal that this transition is mainly driven by the order-disorder transformation of the 4-methoxypiperidinium cations. Furthermore, it also features a promising photoluminescence performance with blue-light emission and a long lifetime of 25.34 ns. It is anticipated that this study will expand the family of hybrid perovskites exhibiting high-temperature phase transitions and offer valuable guidance for the design of new NLO switching materials with superior optoelectronic properties.

Coupled Kite-to-Square Distortion Transition and Physical Properties in 2D Lead Halide Perovskite

2D lead halide perovskites showcase diverse electrical and optoelectrical properties due to their adaptable structural distortion, which dictates the symmetry characteristics of the material. To accommodate the geometric shape of the cation, the inorganic layer of the 2D perovskite often undergoes specific distortions such as lead-halide bond length elongation/compression and lead atom displacement. The resultant distortion manifests as a quadrilateral shape formed by Pb atoms from four adjacent four octahedrons. The degree of distortion increases as the quadrilateral deviates further from a square shape and vice versa. This quadrilateral shape not only visually represents the magnitude of distortion but also confirms its direction. During the transition from kite to square distortion under external stimuli, the positions of the Pb atoms vividly illustrate the symmetry-breaking process, corresponding to a shift from high to low symmetry states. The electrical and optoelectronic properties, including ferroelectricity, pyroelectricity, piezoelectricity, nonlinear optical properties, and characteristics related to bulky photovoltaic effects, some of them exhibit direction dependence nature. This perspective employed a visible structural distortion approach to elucidate symmetry breaking and coupling distortion transitions with eight optoelectronic physical properties in 2D layered perovskite. We review recent research advancements and outline current challenges that help us to understand the structure-property relationship of 2D perovskite.

Investigating the Structure-property Relationships of Two Cd-based Hybrid Multifunctional Compounds with High Tc, Bright Fluorescence and Wide Band-gap

Organic-inorganic hybrid multifunctional materials have shown significant application in lighting and sensor fields, owing to their prominent performance and diversity structures. Herein, we synthesized two multifunctional compounds: (propyl-quinuclidone)2 CdBr4 (1) and (F-butyl-quinuclidone)2 CdBr4 (2). By introducing light-emitting organic cation with flexible long chain, 1 and 2 exhibit excellent transition properties and bright blue-white fluorescence. Then, combine fluorescence lifetime and first-principal calculation, providing evidence for the electron transfer emission. Subsequently, investigated the impact of substituent carbon chain length (methyl to butyl), structural rigidity (C-C to C-F) and halide framework (Cl to I) on the fluorescence properties. Results indicate that Cd⋅⋅⋅Cd distance and structural rigidity play an important role in fluorescence. Overall, our research provides valuable insight and example for chemical modifications enhance compound performance.

Silver/Antimony-Base Multifunctional Double Perovskite with H/F Substitution Enhance Properties

Two-dimensional double perovskites have experienced rapid development due to their outstanding optoelectronic properties and diverse structural characteristics. However, the synthesis of high-performance multifunctional compounds and the regulation of their properties still lack relevant examples. Herein, we synthesized two multifunctional compounds, (C6H14N)4AgSbBr8 (1) and (F2-C6H12N)4AgSbBr8 (2), which exhibit high solid-state phase transition temperature, bistable dielectric constant switching, second harmonic generation (SHG), and bright emission. Through H/F substitution, the transition temperature increases and achieves a smaller band gap attributed to reduced interlayer spacing. Furthermore, we investigated the broad emission mechanism of the compounds through first-principles calculation and variable-temperature fluorescence, confirming the presence of the STE1 emission. Our work provides insight into the further development of multifunctional compounds and chemical modification that enhances compound properties.