Reversible phase transition, dielectric and fluorescent properties of chiral 3D double perovskites

Organic-inorganic hybrid rare-earth double perovskite materials, as a novel multifunctional material system, have demonstrated broad application prospects in ferroelectrics, ferroelastics, piezoelectrics, ferromagnetics, superconductivity, and optoelectronic devices due to their unique organic-inorganic synergistic effects and the 4f electronic characteristics of rare-earth ions. However, current research predominantly focuses on non-chiral systems, while the integration of chiral organic amines with three-dimensional bimetallic perovskite frameworks remains less explored. In this study, based on a molecular engineering strategy, we successfully synthesized two novel chiral hybrid double perovskite compounds [R-3-HDMP]₂RbSm(NO₃)₆ (1) and [S-3-HDMP]₂RbSm(NO₃)₆ (2) (3-HDMP = hydroxy‑N,N-dimethylpyrrolidinium) through precise modification of azacyclic amine skeletons with chiral hydroxyl groups, followed by self-assembly with alkali metal salts and rare-earth metal salts in a 2:1:1 stoichiometric ratio. The enantiomeric configurations of both compounds were demonstrated through vibrational circular dichroism (VCD) spectroscopy. The structures of the compounds were characterized by the variable temperature X-ray single-crystal diffractometer. A differential scanning calorimeter was used to reveal the significant reversible phase transition behavior of 1 and 2 near 251 K/239 K. Meanwhile, the dielectric constant was evaluated to show that stepwise dielectric anomalies occurred near the phase transition temperature. In addition, the fluorescence spectra revealed the characteristic emission behavior of Sm³⁺. Obvious peaks were observed at 564 nm (corresponding to the ⁴G_5/2 → ⁶H_5/2 transition), 597 nm (corresponding to the ⁴G_5/2 → ⁶H_7/2 transition) and 646 nm (corresponding to the ⁴G_5/2 → ⁶H_9/2 transition), confirming that the energy level structure of rare earth ions in the hybrid system was well preserved. This study not only expands the material library of chiral hybrid perovskites but also provides new ideas for the collaborative design of multiferroic materials and optoelectronic functional materials.