Chirality‐Dependent Photoluminescence Redshift of 2D Perovskites Under High Pressure

ABSTRACT The precise discrimination between the racemate and its enantiomers is critical in materials science. Given the nonintuitive limitation of traditional methods, luminescence‐based identification translates microscopic structural differences into macroscopic optical signals, providing an ideal pathway for visual chiral identification. However, subtle luminescence disparity between racemates and enantiomers, coupled with scarce mechanistic insights, hinders the development of this field. Herein, using (Rac, S, R)‐3BrMBA 2 PbI 4 2D perovskites as paradigms, a visual identification window based on high‐pressure‐induced chirality‐dependent luminescence redshift is constructed; within 0–8 GPa, Rac‐3BrMBA 2 PbI 4 exhibits a remarkable transition from green to red emission, whereas S‐ and R‐3BrMBA 2 PbI 4 remain green‐emitting. Excited‐state and electron‐hole effective mass calculations substantiate the free‐exciton origin of emission. Comparative band and structural analyses reveal that the remarkable redshift of Rac‐3BrMBA 2 PbI 4 stems from substantial direct bandgap reduction, induced by stable octahedral contraction within its high‐symmetry structure. Conversely, pressure induces asymmetric halogen bond formation and enhances asymmetric hydrogen bonds in chiral enantiomers. This amplified asymmetry significantly increases the spin‐splitting via chirality transfer but facilitates inefficient phonon‐assisted indirect transitions and the limited bandgap narrowing, limiting the emission redshift. This work leverages high pressure to amplify luminescence disparity between the racemate and enantiomers, elucidating symmetry's pivotal role in 2D perovskite emission and offering a new perspective for visual chiral identification.