Three-Dimensional Perovskite Phase Transition Materials with Switchable Second Harmonic Generation Properties Introduced by Homochiral (1 S ,4 S )-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 [1 S ,4 S 2,5-2.2.1-H ₂ dabch]RbX ₃ ·0.5H ₂ O (X = Cl, 1 ; Br, 2 ; I, 3 ) based on the chiral 1 S ,4 S -2,5-diazabicyclo[2.2.1]heptane (1 S ,4 S -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 P 2 ₁ 2 ₁ 2 ₁ , 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 [RbX ₃ ] _n and the organic cation [1 S ,4 S -2,5-2.2.1-H ₂ dabch] 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.