Dual switching of dielectric and SHG triggered by thermal driven helical axis transformation with fluorescence characteristics

Abstract

Organic–inorganic hybrid perovskites (OIHPs) have aroused widespread interest because of their exceptional performance in thermal, optical, electric, and information storage applications. However, it is relatively rare for OIHPs to respond to both temperature and light, which limits their multifunctional applications. Therefore, in this article, by incorporating [N,N-dimethyl-pyrrolidinium]⁺ as the cation, in combination with lead halide exhibiting semiconducting properties, two OIHPs (N,N-dimethyl-pyrrolidinium)PbCl₃ (compound 1) and (N,N-dimethyl-pyrrolidinium)PbBr₃ (compound 2) were successfully obtained. These compounds not only exhibit two phase transitions but also demonstrate second harmonic generation (SHG) and dielectric switching near 270 K and 278 K, respectively. Surprisingly, due to the presence of helical axes in the inorganic framework, both compounds crystallize in the chiral P6₁ space group below room temperature. The first phase transition results from the transformation of the 6₁ to the 6₃ screw axes in the inorganic framework, while the second phase transition is attributed to the order-to-disorder transformation of cations. This study provides a new perspective for designing polar multifunctional switchable phase materials.