Competitive Chirality Induction in Two-dimensional Germanium Iodide Perovskites Enabling Highly Anisotropic Nonlinear...

Chiral metal halide perovskites (CMHPs) are a promising class of chiroptical materials with significant potential applications in chiral-optoelectronic and chiral-spintronic devices. However, their chirality induction generally stems from the incorporation of chiral ligands, which constitutes compositional diversity and functional versatility. Herein, we report a significant chiral expression resulting from two distinct mechanisms: chirality transfer induced by chiral organic cations and mirror symmetry breaking driven by stereochemically active lone pairs, both contributing to controlled chirality induction. Homochiral germanium iodide perovskites, (R/S-BrMBA)₂GeI₄ (R/S is Rectus/Sinister) can be achieved by employing chiral (R/S)-BrMBA cations to induce chirality via hydrogen bonding. In contrast, two enantiomorphous helical germanium iodide perovskites, P/M-(rac-BrMBA)₂GeI₄ (P/M is Plus/Minus and rac is racemic), are formed via the co-assembly of racemic rac-BrMBA cations and germanium iodide networks, where chirality arises from spontaneous symmetry breaking induced by the stereochemically active 4s² electron pair. Remarkably, benefiting from the inherent chirality, both (R-BrMBA)₂GeI₄ and P-(rac-BrMBA)₂GeI₄ crystals exhibit exceptional anisotropic nonlinear optical properties with large anisotropy factors (g_SHG-CD) up to 0.71 and 0.83 and laser damage thresholds of 697.5 and 535.2 GW cm^{- 2}, surpassing most previously reported CMHPs. This study provides insight into the interplay of chiral organic ligands and inorganic ions in the chiral induction, transfer, and functions of metal halide perovskites.