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.