Deciphering the electronic and structural origin of chiroptical activity of chiral 2D perovskites

Understanding the structure-chiroptical activity relationship in chiral perovskites is of great significance as it provides a pathway to control light-matter interactions. Although many reports have shown various chiral structures with distinctive chiroptical responses, a clear structure-property relationship is still missing, partially stemming from the poor understanding of the optical activity mechanism. For instance, it remains unclear if and how the chiroptical activity is related to exciton spin splitting. Herein, we used magnetic circular dichroism to probe the exciton spin splitting in a series of chiral 2D perovskites. Our results show that the anisotropy factor of circular dichroism is indeed proportional to the exciton spin splitting energy, with larger splitting energy yielding larger anisotropy factors. Further structural analysis showed that the splitting energy is closely correlated with both the in-plane and out-of-plane distortion structural parameters of the inorganic lattice. Our work provides an important mechanistic understanding of chiroptical activity and establishes the structure-property relationship for 2D chiral perovskites.