Unique cation-template three-dimensional hybrid material demonstrates dielectric switchable response

The halogen substitution strategy of inorganic skeletons triggers dielectric and band gap regulation of hybrid perovskites

Organic-inorganic hybrid perovskites (OIHPs) with dielectric switching functions have aroused comprehensive scientific interest, benefitting from their promising applications in sensors and information storage. However, to date, most of these materials discovered thus far possess a single function and are limited in their applicability, failing to meet the requirements of diverse applications. Moreover, the discovery of these materials has been largely serendipitous. Building multifunctional OIHPs with dielectric switching and semiconductors remains a daunting task. In this context, by introducing [C7H16N]+ as cations and in combination with lead halide with semiconducting properties, two OIHPs [C7H16N]PbI3 (1) and [C7H16N]PbBr3 (2) ([C7H16N]+ = (cyclopropylmethyl) trimethylammonium) have been successfully designed. They have dielectric switching properties close to 253 and 279 K and semiconducting behavior with band gaps of 2.67 and 3.22 eV. The phase transition temperature increased by 26 K through halogen substitution. In summary, our findings in this study provide insights into the application of the halogen substitution regulation strategy and open up new possibilities for designing perovskite semiconductors with dielectric switching functionality.

Halogen engineering of organic-inorganic hybrid perovskites displaying nonlinear optical, fluorescence properties and phase transition

In order to meet the needs of social development, increasing research attention has been paid to multifunctional molecular-based phase-transition materials. The traditional phase-transition materials with a single functional property can be transformed into magnificent ones by adding additional functional properties-for instance photoluminescence and magnetic order- because having two or more functional properties simultaneously greatly broadens the fields of their applications. At present, there are very few multifunctional phase-transition materials showing excellent performance, and the crystal structure design and performance optimization of materials still need to be studied in depth. Herein, we report the development of two organic-inorganic hybrid materials: (MBA)₂ZnI₄ (1, MBA = 4-methoxybenzylammonium) with switchable dielectricity and a high phase-transition temperature (T_c = 359.55 K), and (MBA)₂ZnBr₄ (2) with green luminescence (λ_exc = 314 nm) and nonlinear optical properties (0.75× KDP). A two-dimensional (2D) fingerprint analysis of the Hirshfeld surface plots revealed a significant difference between the hydrogen-bonding interaction before the phase transition and that afterwards. The two compounds were further verified, from energy band structure calculations, to be direct-band-gap semiconductors. In conclusion, this work has provided a viable strategy, involving the application of chemical modifications, for designing various functional materials.

Three-Dimensional Perovskite Phase Transition Materials with Switchable Second Harmonic Generation Properties Introduced by Homochiral (1S,4S)-2,5-Diazabicyclo[2.2.1]-heptane

Switchable second harmonic generation (SHG) materials have potential applications in information storage, signal processing, and so on because they can switch between SHG-on and SHG-off states. In this work, we designed and synthesized three organic-inorganic hybrid Rb halide three-dimensional (3D) perovskite materials [1S,4S 2,5-2.2.1-H₂dabch]RbX₃·0.5H₂O (X = Cl, 1; Br, 2; I, 3) based on the chiral 1S,4S-2,5-diazabicyclo[2.2.1]heptane (1S,4S-2,5-2.2.1-dabch). The selection of homochiral organic cations ensures that the compounds 1∼3 crystallize in the noncentrosymmetric and chiral space group P2₁2₁2₁, which further leads to reversible SHG responses of the three compounds. Through differential scanning calorimetry (DSC) and dielectric measurements, it revealed that the phase transition point of the compounds 1∼3 increased with RbCl, RbBr, and RbI. This is because the hydrogen interaction H···X between the inorganic framework [RbX₃]_n and the organic cation [1S,4S-2,5-2.2.1-H₂dabch]²⁺ is increased with the order of I > Br > Cl. This study can provide an effective molecular design strategy for the exploration and construction of temperature-tunable SHG switching materials.

Metal ion induced dual switchable dielectric and luminescent properties in hybrid halides

A new multi-functional organic-inorganic hybrid compound was successfully obtained by regulating metal halides. Apart from excellent luminescence properties, in particular, the introduction of a Mn halide successfully achieved a dual-switchable dielectric property, which could lead to very interesting exploration in sensors.

Metal ion modulation triggers dielectric double switching and green fluorescence in A2MX4-type compounds

Multifunctional switching materials show great potential for applications in sensors, smart switches, and other fields due to their ability to integrate different physical channels in one single device. However, multifunctional responsive materials with multiple switching and luminescence properties have rarely been reported. Here, we report three organic-inorganic hybrids: [TMAA]₂[CoCl₄] (compound 1), [TMAA]₂[CdBr₄] (compound 2) and [TMAA]₂[MnCl₄] (compound 3). Compound 1 and compound 2 undergo two reversible phase transitions at high temperature (328.95/359.25 K and 350.45/393.15 K, respectively). Since the inorganic skeleton has a strong influence on the luminescence properties of such structured substances, Cd and Co were replaced with Mn, after which compound 3 was obtained as expected. The above strategy triggered bright green luminescence with a quantum yield of 35.19%, and significantly increased the phase transition temperature of compound 3 to above 400 K. The above results show that the regulation of the inorganic skeleton provides a new strategy for researchers to develop dual phase change/luminous materials.

Above-Room-Temperature Ferroelastic Phase Transitions in Two Tetrafluoroborate-Based Hexagonal Molecular Perovskites

ABX₃-type molecular perovskites provide an important platform to tune phase transitions, via judiciously choosing A-, B-, and X-site components, to approach advanced functional materials for applications. Although tetrafluoroborate can act as X-site component to assemble ten instances of ABX₃ molecular perovskites, only two of them possess hexagonal perovskite structures. Herein, we report two tetrafluoroborate-based hexagonal molecular perovskites, A[Na(BF₄)₃], by judiciously choosing two different A-site cations: 1-methyl-1,4-diazabicyclo[2.2.2]octane-1,4-diium (Hmdabco²⁺) for 1 and 1-methylpiperazine-1,4-diium (H₂mpz²⁺) for 2. They have high-temperature phases in the same space group (P6₃/mmc) revealing highly disordered A-site cations. Upon cooling, 1 undergoes two-step P6₃/mmc ↔ P3̅c1 ↔ P2₁/n transitions at 344 and 338 K, respectively, including a ferroelastic one (3̅mF2/m) accompanied by a spontaneous strain of 0.013. In contrast, the smaller H₂mpz²⁺ cation with more adoptable conformations induces a one-step sharp P6₃/mmc ↔ P2₁/c ferroelastic transition (6/mmmF2/m(s)) at 418 K in 2, leading to more significant symmetry breaking and a considerable spontaneous strain of 0.129. This study provides important clues to modulate structural phase transitions by tuning diverse components for the multicomponent dense hybrid crystals.

Near-room-temperature dielectric switch and thermal expansion anomaly in a new hybrid crystal: (Me2NH2)[CsFe(CN)5(NO)]

A new hybrid crystal, (Me2NH2)[CsFe(CN)5(NO)], featuring a double-layered nitroprusside-based inorganic framework with cubic-like cages encapsulating organic cations, undergoes a near-room-temperature phase transition accompanying with dielectric switch and thermal expansion anomaly....

Thermally stimuli-responsive materials with transformable double channels of nonlinear optical and dielectric

Organic-inorganic hybrid materials have received extensive attention and in-depth research in the past few decades due to their superior properties and potential applications in storage, sensing, dielectric switches, actuators and...