Two 3D Rubidium Halide Organic–Inorganic Hybrid Perovskite Ferroelectrics Templated by Quasi‐Spherical Organic Amine 1,4‐Diazabicyclo[3.2.2]nonane

Abstract

The emergence of (CH3NH3)PbI3 has brought the development of three‐dimensional (3D) organic‐inorganic hybrid perovskite (OIHP) structures with ABX3 type to a higher level; however, most 3D frameworks are constructed by corner‐sharing of BX6 octahedra. Herein, we substituted the spherical molecule 1,4‐diazabicyclo[2.2.2]octane (2.2.2‐dabco) with 1,4‐diazabicyclo[3.2.2]nonane (1,4‐3.2.2‐dabcn) as a template to react with RbX (X=Br, I) in the corresponding HX acids under the consideration of reducing the molecular symmetry. Two 3D OIHP compounds [1,4‐3.2.2‐H2dabcn]RbI3⋅H2O (1) and [1,4‐3.2.2‐H2dabcn]RbBr3 (2) crystallized in non‐centrosymmetric point group mm2 before the phase transition point were isolated. Among them, the 3D inorganic framework of 1 is constructed by sharing the corner of [RbI6] octahedra, while that of 2 is constructed by sharing the corner and face of [RbBr6] octahedra to acquire large cavities to accommodate the organic amine cation [1,4‐3.2.2‐H2dabcn]2+; this 3D framework type is unprecedented in the OIHPs. As expected, compounds 1 and 2 exhibit reversible phase transition, dielectric and second harmonic generation (SHG) and ferroelectric properties, in which the phase transition temperature of 2 at 374 K is much higher than compound 1 at 280 K.

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

“…As shown in Figure , compound 1 shows a typical 3D OIHP structure, in which the inorganic rubidium halide component forms the 3D framework through octahedron [RbX 6 ] by sharing the vertices. To be noted, compared with the reported Rb halide 3D perovskite structures [(1,4-3.2.2-H 2 dabcn)­RbBr 3 ] and [(1,5-3.2.2-H 2 dabcn)­RbX 3 ] (X = Br, I) templated by 1,4-diazabicyclo[3.2.2]­nonane (1,4-3.2.2-dabcn) or 1,5-diazabicyclo[3.2.2]­nonane (1,5-3.2.2-dabcn), in the 3D cavity of compound 1 , in addition to the presence of 1 S ,4 S -2,5-diazabicyclo­[2.2.1]­heptane, water molecules are also found to be embedded in it. This is because the size of 1 S ,4 S -2,5-2.2.1-dabch is small, and itself alone cannot completely occupy the cavity formed by the inorganic framework, and water molecules are required to join together to maintain the stability of the 3D framework.…”

“…Interestingly, because the chiral space group belongs to one of the noncentrosymmetric space groups, the utilization of chiral organic molecules into OIHP can break its inherent symmetry and effectively reduce structural symmetry. − Therefore, it is more likely to obtain SHG-responsive substances by designing chiral materials. When designing synthetic molecules, choosing chiral centers gives the crystal a greater probability of crystallizing in polar space groups. ,− …”

“…Furthermore, the introduction of quasi-spherical molecules makes the crystal have asymmetry and dipole moment, which makes it easier to generate an SHG response. , In recent years, the quasi-spherical molecules such as 1,4-diazabicyclo[2.2.2]­octane, 1,5-diazabicyclo[3.2.1]­octane, 1,4-diazabicyclo[3.2.2]­nonane, and 1,5-diazabicyclo[3.2.2]­nonane have been widely used to synthesize multifunctional compounds with reversible phase transition, dielectric, SHG effects, and ferroelectric properties. ,,, This is because the quasi-spherical molecules are easy to rotate at high temperatures and disorderly form spherical structures, while they are in an ordered state at low temperatures. Therefore, the introduction of the quasi-spherical structure provides the possibility to enrich the phase transition and frequency doubling materials. ,, …”

Tuning the luminescent properties of a three-dimensional perovskite ferroelectric (Me-Hdabco)CsI3via Sn(ii) doping

“…Recently, Cai et al isolated a family of 3D molecular ferroelectric perovskites based on alkaline halides by tuning metal ions, halogen ions, and organic cations. [17][18][19] The ferroelectric properties of the reported 3D alkaline halide perovskite have been extensively studied; achieving luminescent performance of alkaline halide perovskites is a major challenge because of the alkaline halide inorganic framework without photoluminescence.…”

Dehydration Induced a Structural Transformation into a One-Dimensional Hybrid Perovskite with Second Harmonic Generation and Dual Dielectric Switching

“…The regulation of the structural transformation in hybrid organic–inorganic halides is now predominantly focused on the manipulation of cations and anions, which derives from the ordered–disordered motions of organic cations or the distortion of inorganic frameworks. − However, owing to the intricate intermolecular network between the cations and anions, it remains challenging to design functional compounds with the desired performance and the exploration of the relationship between structure and property. − Recently, the desolvation of hybrid organic–inorganic perovskite, referring to the removal of guest solvent molecules from crystals, has emerged as a novel method to induce structural transformation and regulate optical and electronic properties. − The common approaches for such desolvation encompass evaporation, freeze-drying, solvent extraction, etc. Among them, evaporation is the most widely used method where the material containing a solvent is heated, allowing the solvent molecules to evaporate and sometimes leading to structural transformation .…”