Homochiral and Heterochiral Cation Mixing in 2D Perovskites for Enhanced Structural Asymmetry and Spin Splitting
Yiyang Xie, Heshan Hewa-Walpitage, Jack Morgenstein, Volker Blüm, Z. Valy Vardeny, David B. Mitzi
Abstract
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 (Δ E = 78.5 meV), among the largest reported for PbI 4 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.