A Three-Dimensional Molecular Perovskite Ferroelastic with Two-Step Switching of Quadratic Nonlinear Optical Properties Tuned by Molecular Chiral Design

Molecular
perovskite materials have recently attracted extraordinary
interest from the academic community owing to their excellent multifunctional
properties. Nevertheless, although massive efforts have been made,
molecular ferroelastics with three-dimensional (3D) perovskite structures
are still rare. Herein, we report two 3D organic–inorganic
hybrid perovskites [(2-hydroxy-propyl)-tripropyl-ammonium]­[Mn­(dca)3] (1) and [(2-hydroxy-1-methyl–ethyl)-tripropyl-ammonium]
[Mn­(dca)3] (2) [dca = dicyanamide, N­(CN)2]. The different position of the chiral center results in
a tremendous difference in the properties. Compound 1 displays only one phase transition; however, intriguingly, 2 has three phase transitions and represents ferroelastic
behavior with exceptional two-step switching of quadratic nonlinear
optical (NLO) properties. To the best of our knowledge, this is the
first molecular ferroelastic with two-step switching of quadratic
NLO properties. The results demonstrate that the molecular chiral
design works, and this finding opens up a new avenue to designing
multifunctional molecular perovskite materials.

近年来，由于分子钙钛矿材料卓越的多功能性，该领域吸引了学术界极大的关注。尽管已经投入了大量的研究努力，但具有三维（3D）钙钛矿结构的分子铁电体仍然较为罕见。在本研究中，我们报道了两种三维有机-无机杂化钙钛矿 [(2-羟基丙基)-三丙基铵]­[Mn­(dca)3] (1) 和 [(2-羟基-1-甲基-乙基)-三丙基铵] [Mn­(dca)3] (2) [dca = dicyanamide, N­(CN)2]。手性中心的不同位置导致了性能的巨大差异。化合物1仅表现出一种相变；然而，引人注目的是，化合物2具有三种相变，并展现出非凡的两步切换的二次非线性光学（NLO）性能。据我们所知，这是第一种具有二次NLO性能两步切换的分子铁电体。这些结果证明了分子手性设计的有效性，并为设计多功能分子钙钛矿材料开辟了新的途径。