Unraveling Lattice Void Occupancy Engineering for Regulating Optical/Dielectric Responses in Hybrid Crystals

Organic–inorganic hybrid phase transition materials have become a key direction in the current research of advanced functional materials due to their unique structural designability, excellent thermal stability, and rich functional diversity. However, the mechanisms by which the dynamic evolution of the lattice microenvironment regulates the phase transition behavior are still poorly understood. Here, we explored the relationship and modulation mechanism between lattice void occupancy and phase transition temperature and clarified how microstructure modulation precisely controls phase transition temperature while optimizing optical/electrical response properties. By means of halogen engineering (F → Cl → Br) to modify the [TEMA]+ cation (TEMA = triethylmethylammonium), we synthesized four phase transition materials [TEMA][Cd(SCN)3], [TEFA][Cd(SCN)3], [TECA][Cd(SCN)3], and [TEBA][Cd(SCN)3] (TEFA = triethylfluoromethylammonium, TECA = triethylchloromethylammonium, TEBA = triethylbromomethylammonium). The halogen substitution strategy can effectively modulate the lattice void occupancy to increase the phase transition temperature, in which the Cl/Br substitution-induced halogen bonding of the inorganic frameworks can be directed to build up the polar structure and produce nonlinear optical switching effects. This study illustrates the intrinsic correlation of structure–property relationship of organic–inorganic hybrid phase transition materials, which provides innovative ideas and a theoretical basis for the development of high-performance phase transition materials.