[C5 H12 N]SnCl3 : A Tin Halide Organic-Inorganic Hybrid as an Above-Room-Temperature Solid-State Nonlinear Optical Switch

Phase Transitions and Dynamics in Mixed Three- and Low-Dimensional Lead Halide Perovskites

Lead halide perovskites are extensively investigated as efficient solution-processable materials for photovoltaic applications. The greatest stability and performance of these compounds are achieved by mixing different ions at all three sites of the APbX3 structure. Despite the extensive use of mixed lead halide perovskites in photovoltaic devices, a detailed and systematic understanding of the mixing-induced effects on the structural and dynamic aspects of these materials is still lacking. The goal of this review is to summarize the current state of knowledge on mixing effects on the structural phase transitions, crystal symmetry, cation and lattice dynamics, and phase diagrams of three- and low-dimensional lead halide perovskites. This review analyzes different mixing recipes and ingredients providing a comprehensive picture of mixing effects and their relation to the attractive properties of these materials.

Oxidation-Induced Dissolution Recrystallization Structural Transformation Strategy Enhanced Nonlinear Optical Effect of Hybrid Chiral Tin Bromide Single Crystals

In order to reveal the integrated effect of inorganic lattice structure disturbances and chiral ligands on the structure of tin halide hybrid materials, we show the synthesis, crystal growth, dissolution recrystallization structural transformation (DRST), optical properties, energy band structure, and nonlinear optical properties of a class of chiral tin bromide R/S-2-mpip[SnBr3]Br (2-mpip is 2-methylpiperazinium) and R/S-2-mpipSnBr6 for the first time. The formation of R/S-2-mpipSnBr6 in solution was interestingly caused by irreversible DRST of R/S-2-mpip[SnBr3]Br. The second-harmonic generation response of the new phase R-2-mpipSnBr6 is significantly enhanced compared to that of the initial phase R-2-mpip[SnBr3]Br. These structural transformations of chiral tin bromides reflect, to some extent, the DRST commonality of the tin halide family induced by oxidation and serve as a starting point for investigating the structural chirality and asymmetry of chiral metal hybrid halides.

Organic Cation Modulation Triggered Second Harmonic Response in Manganese Halides with Bright Fluorescence

Zero-dimensional (0D) hybrid manganese halides have been recently synthesized and exhibited rich functional properties including fluorescence, ferroelectrics, and ferromagnetism. However, few studies on second-harmonic generation (SHG) behaviors of manganese halide crystals have been reported, presumably owing to the d-d transitions. Here, we report three manganese bromides, [TEA]₂MnBr₄ (TEA⁺ = tetraethylammonium; 1), [BTEA]₂MnBr₄ (BTEA⁺ = benzyltriethylammonium; 2), and [BTMA]₂MnBr₄ (BTMA⁺= benzyltrimethylammonium; 3), with linear and nonlinear optical properties via benzyl or ethyl/methyl substitution strategies. They feature 0D structures containing isolated [MnBr₄]^2- anions and quaternary ammonium cations with different sizes inserted for charge balance. They all show green phosphorescence, and 2 possesses good luminescence efficiency with a quantum yield of 97.8%, which is larger than those of 1 (79%) and 3 (72%). Specifically, acentric 1 and 3 present effective SHG responses about 0.48 and 0.59 times that of KDP, respectively. The result throws light on the new properties of the hybrid manganese halides and provides a new way to develop novel nonlinear optical-active organic-inorganic hybrid metal halides.

Symmetry breaking of A3M2X9-type perovskite derivatives induced by polar quaternary ammonium cations: achieving efficient nonlinear optical properties

Low-dimensional organic-inorganic metal halides, especially lead-free perovskites, are attracting increasing attention because of their environmentally friendly processing, flexible structures, chemical stability, and promising nonlinear optical properties. Herein, we report a new stable polar 0D lead-free hybrid bismuth chloride to enable the second-harmonic generation (SHG) active material (BTA)₃Bi₂Cl₉ (BTA = benzyltriethylammonium, C₆H₅CH₂N(C₂H₅)₃⁺) that was obtained by the antisolvent vapor diffusion method and crystallized in the polar Cc space group. Its structure features organic cations surrounded by face-sharing [Bi₂Cl₉]^3- dimers. (BTA)₃Bi₂Cl₉ exhibits a wide direct bandgap (3.21 eV) and a strong phase-matchable SHG conversion efficiency (1.39 × KDP). Theoretical calculation reveals that the SHG response is owing to the synergistic effect of distorted inorganic [Bi₂Cl₉]^3- anions and polar organic BTA⁺ cations. This work not only enriches the family of organic-inorganic A₃M₂X₉ (A = monovalent cations; M = trivalent metal ions; and X = halide ions) NLO crystals but also provides the possibilities for further designing novel lead-free semiconducting piezoelectric, pyroelectric and ferroelectric materials.

Chiral Hybrid Copper(I) Halides for High Efficiency Second Harmonic Generation with a Broadband Transparency Window

Chiral hybrid organic-inorganic metal halides (HOMHs) with intrinsic noncentrosymmetry have shown great promise for applications in second-order nonlinear optics (NLO). However, established chiral HOMHs often suffer from their relatively small band gaps, which lead to negative impacts on transparent window and laser-induced damage thresholds (LDT). Here, we have synthesized two chiral HOMHs based on Cu^I halides, namely (R-/S-MBA)CuBr₂ , which feature well-balanced NLO performances with a highly efficient SHG response, outstanding optical transparency, and high LDT. The effective second-order NLO coefficient of (R-MBA)CuBr₂ has been determined to be ≈24.7 pm V^-1 , which is two orders of magnitude higher than that of their Cu^II counterparts. This work shows the promising potential of Cu^I -based chiral HOMHs for nonlinear photonic applications in wide wavelength regions.

Near-Infrared Phosphorescent Hybrid Organic-Inorganic Perovskite with High-Contrast Dielectric and Third-Order Nonlinear Optical Switching Functionalities

Hybrid organic-inorganic perovskites providing integrated functionalities for multimodal switching applications are widely sought-after materials for optoelectronics. Here, we embark on a study of a novel pyrrolidinium-based cyanide perovskite of formula (C4H10N)2KCr(CN)6, which displays thermally driven bimodal switching characteristics associated with an order-disorder phase transition. Dielectric switching combines two features important from an application standpoint: high permittivity contrast (Δε' = 38.5) and very low dielectric losses. Third-order nonlinear optical switching takes advantage of third-harmonic generation (THG) bistability, thus far unprecedented for perovskites and coordination polymers. Structurally, (C4H10N)2KCr(CN)6 stands out as the first example of a three-dimensional stable perovskite among formate-, azide-, and cyanide-based metal-organic frameworks comprising large pyrrolidinium cations. Its stability, reflected also in robust switching characteristics, has been tracked down to the Cr3+ component, the ionic radius of which provides a large enough metal-cyanide cage for the pyrrolidinium cargo. While the presence of polar pyrrolidinium cations leads to excellent switchable dielectric properties, the presence of Cr3+ is also responsible for efficient phosphorescence, which is remarkably shifted to the near-infrared region (770 to 880 nm). The presence of Cr3+ was also found indispensable to the THG switching functionality. It is also found that a closely related cobalt-based analogue doped with Cr3+ ions displays distinct near-infrared phosphorescence as well. Thus, doping with Cr3+ ions is an effective strategy to introduce phosphorescence as an additional functional property into the family of cobalt-cyanide thermally switchable dielectrics.

Exploring a Fatigue-Free Layered Hybrid Perovskite Ferroelectric for Photovoltaic Non-Volatile Memories

Through a functional unit-transmutation strategy, a fatigue-free layered hybrid perovskite ferroelectric (C₆ H₅ CH₂ NH₃ )₂ CsPb₂ Br₇ (BCPB) has been developed, which demonstrates stable spontaneous polarization (P_s ) of 6.5 μC cm^-2 and high Curie temperature up to 425 K. Meanwhile, BCPB shows splendid bulk photovoltaic effect (BPVE) properties with noticeable zero-bias photocurrent density (5 μA cm^-2 ), and high on/off switching ratio of current (over 3×10⁵ ); these merits even overmatch the most known ferroelectric semiconductor BiFeO₃ . The unique structure with self-regulated net electrical charged layers gives rise to the fatigue-free feature of P_s and BPVE (no significant fatigue after 10⁸ polarity switching cycles), promoting the potential applications of BCPB in photovoltaic non-volatile memories. This work offers an efficient approach for exploring fatigue-free semiconducting ferroelectrics as well as excavates their further applications in next-generation electronic devices.

Stepwise Dielectric Switching Occurs in Two Photo-Responsive Complexes Possessing Two-Dimensional Structures

Two organic-inorganic hybrid complexes, (CH₃NH₃)Na[Fe(CN)₅NO]·H₂O (1) and (CH₃NH₃)₂[Fe(CN)₅NO] (2), which exhibit stepwise dielectric switching as well as photo-induced structural transformation, are synthesized and examined. In these two compounds, the photo-responsive complex anions, [Fe(CN)₅NO]^2-, connected by Na⁺ through N-Na coordination bonds or CH₃NH₃⁺ through N···H-N hydrogen bonds, form two-dimensional structures. One organic cation, CH₃NH₃⁺, that resides in the intralaminar cavity and plays a role as a template, undergoes a temperature-controlled order-disorder structural phase transition. As the frozen-thawed state change of the polar organic cations modifies the polarizability of materials, stepwise dielectric switching is observed at the phase transition temperature. Furthermore, the photo-induced linkage isomerism of [Fe(CN)₅NO]^2- building block survives in the new compounds at the low-temperature range, which is verified by variable-temperature IR spectra after photo-irradiation. The coexistence of switchable dielectric properties and photo-induced structural variation suggests multiple optical-electric roles of the present materials.

Above room-temperature dielectric switching and semiconducting properties of a layered organic-inorganic hybrid compound: (C6H12N)2Pb(NO3)4

The well-studied star compound, CH3NH3PbI3, has attracted plenty of attention because of its remarkable optical and electrical properties. Consequently, new switching multifunctional hybrid compounds can be widely used in many fields such as solar cells, light-emitting diodes, optical data storage and so on. Therefore, switching multifunctional hybrid compounds with dielectric and semiconducting properties simultaneously will also find roles in the next generation of optoelectronic coupling materials. In fact, discovering an effective method to synthesize (multi)functional hybrid materials remains a pressing challenge. Thanks to the "quasi-spherical theory" proposed by Xiong et al., we used 7-azabicyclo[2.2.1]heptane as the quasi-spherical cation to construct molecule-based crystalline materials that exhibit responsive properties. Then, we tried to exploit the knowledge of crystal engineering and coordination chemistry to explain (multi)functional molecular materials. A layered organic-inorganic hybrid compound, (C6H12N)2Pb(NO3)4 (1), was grown and its dielectric switching property and semiconducting behaviour were investigated. Insights from differential scanning calorimetry measurements, variable-temperature X-ray structural studies, and dielectric spectroscopy revealed the origin of the phase transition, which is related to the motion of the organic ammonium and inorganic framework in solid-state crystals. Furthermore, 1 is also a wide bandgap semiconductor with an optical bandgap of 3.53 eV. The realization of switching and semiconducting properties simultaneously in layered Pb-based perovskites has a great significance toward research into hybrid compounds and the development of dielectric-optoelectronic integrated materials.

Molecule-based nonlinear optical switch with highly tunable on-off temperature using a dual solid solution approach

Nonlinear optical switches that reversibly convert between on/off states by thermal stimuli are promising for applications in the fields of photoelectronics and photonics. Currently one main drawback for practical application lies in the control of their switch temperature, especially for the temperature range near room temperature. By mixed melting treatment, here we describe an alloy-like nonlinear optical switch with tunable switch temperature via a dual solid solution approach within the coordination polymer system. We initially prepare a coordination polymer (i-PrNHMe2)[Cd(SCN)3], which functions as a high-contrast thermoresponsive nonlinear optical switch originating from a phase transition at around 328 K. Furthermore, by taking advantage of a synergistic dual solid solution effect, the melt mixing of it with its analogue (MeNHEt2)[Cd(SCN)3], which features an unequal anionic chain templated by an isomeric ammonium, can afford coordination polymer solid solutions with switch temperatures that are tunable in a range of 273-328 K merely by varying the component ratio.

Lead-Free Tin(IV)-Based Organic-Inorganic Metal Halide Hybrids with Excellent Stability and Blue-Broadband Emission

Lead-free zero-dimensional (0D) organic-inorganic metal halide hybrids have recently attracted special attention as luminescent materials. However, their structural stability is still a challenge for the further development. Here, we select Sn⁴⁺ as the B-site inorganic cation and obtain a new tin(IV)-based organic-inorganic metal halide hybrids (C₆N₂H₁₆Cl)₂SnCl₆ with remarkable air stability. (C₆N₂H₁₆Cl)₂SnCl₆ exhibits a blue broadband emission originating from self-trapping excitons (STEs) and the emission intensity remains stable for over three months. When the temperature rises to 450 K, the intensity of photoluminescence can maintain about 50%, indicating the good thermal stability of (C₆N₂H₁₆Cl)₂SnCl₆. This work presents a new strategy toward the tin(IV)-based photoluminescent organic-inorganic metal halide hybrids with environmentally friendly, high stability characteristics.

(C3H9NI)4AgBiI8: a direct-bandgap layered double perovskite based on a short-chain spacer cation for light absorption

A new iodide layered double perovskite (C₃H₉NI)₄AgBiI₈ (IPAB) has been developed based on a short-chain spacer cation, which is the first homologous compound in iodide double perovskites that adopt the Ruddlesden–Popper structure type.

Tin based organic–inorganic hybrid semiconductors with reversible phase transition and dielectric anomaly

Two discrete tin based organic–inorganic hybrid compounds [(FMBA)₂SnX₆] (X = Cl and Br) showed reversible phase transition and dielectric anomaly above 400 K which were originated from the order-disorder of a fluorine-substituted organic amine.

Redox-switching of ternary Ni(ii) and Cu(ii) complexes: synthesis, experimental and theoretical studies along with second-order nonlinear optical properties

The redox-switching behavior of the title compounds has been probed for the Ni(ii) derivatives using time-resolved spectroelectrochemistry under thin-layer conditions.