Homochiral and Heterochiral Cation Mixing in 2D Perovskites for Enhanced Structural Asymmetry and Spin Splitting

Overcoming the constraints of single-cation phases and further enhancing structural asymmetry represent critical objectives for optimizing emergent optoelectronic and spin-related properties in two-dimensional (2D) hybrid organic–inorganic perovskites (HOIPs). Here, we demonstrate homochiral (S/S) and heterochiral (R/S) cation mixing in 2D HOIPs via a 1:1 mixing of S- and R-4-bromo-α-methylbenzylammonium with S-1-methylhexyammonium. The R/S system achieves an enhanced structural asymmetry, marked by a significant Pb–I–Pb bond angle disparity (Δβ = 9.24°), attributed to the distinctive asymmetric templating effects from mixed cations with distinct molecular structures and opposite absolute configurations. Consequently, spin–orbit-coupled hybrid density functional theory (DFT) calculations indicate a substantial spin splitting (ΔE = 78.5 meV), among the largest reported for PbI₄^2–-based 2D HOIPs. Nonequivalent chiral information from homo- and heterochiral mixing further modulates the Cotton effect for the same elemental composition. Our study demonstrates an important materials design strategy for enhancing structural asymmetry and advancing symmetry-breaking-reliant properties in organic–inorganic hybrids.