Amplification of Chirality in Self-Assembled Chiral Perovskite Superstructure Films

Chiral hybrid organic-inorganic perovskites (CHOIPs) represent a distinctive class of chiral materials, exhibiting remarkable potential for facilitating chiral information transfer across multiple length scales. However, the currently reported CHOIPs predominantly rely on the molecular chirality arising from the interaction between chiral organic cations and inorganic backbones, leading to suboptimal chiral expression. Herein, we report the synthesis of a CHOIP superstructure film (R-MBA)_x(S-MBA)_(1-x)BiI₄, which exhibited significantly enhanced chirality through a subtle enantiomeric excess (ee) approach. The implementation of a 20% ee in a mixture of two CHOIP enantiomers resulted in a substantial enhancement of the genuine circular dichroism (CD) asymmetry factor (g_CD > 0.03), exhibiting an increase of more than 50-fold compared to that of the enantiopure film. X-ray diffraction (XRD) analysis revealed that the superstructure adopted an identical crystalline phase to that of the pure enantiomeric ones, suggesting that the observed enhancement does not originate from intracrystalline chirality. Integrating theoretical simulations, we posit that the observed chiral enhancement is predominantly attributed to crystal transfer from the nanoscale, defined as the superstructure chirality formed by mixed enantiomers. These findings establish a novel framework for exploring superstructure chirality in CHOIPs, offering new perspectives for future research in this field.