Mutual Amplification of Chirality Driven by Interfacial Interactions in In Situ Synthesized Perovskite/Polymer Composites

Two‐dimensional hybrid organic–inorganic perovskites (2D HOIPs) are promising for chiral optoelectronics and spintronics. However, long‐range chiral amplification remains difficult because conventional chiral organic spacers mainly induce localized lattice asymmetry. Here, we report an in situ polymerization strategy to construct synergistically coupled 2D tin‐based HOIP/polydiacetylene (L‐(C n ‐NH 3 ) 2 SnBr 4 /PDA) heterostructures. By changing the alkyl‐chain length of L‐(C n ‐NH 3 ) 2 SnBr 4 ( n = 4, 10, 18), the interfacial van der Waals interactions were systematically tuned. This tuning creates a mutual chirality‐amplification feedback loop: the chiral perovskite directs asymmetric PDA polymerization, while PDA provides geometric confinement to amplify the chirality of the perovskite lattice. Among these composites, L‐(C 18 ‐NH 3 ) 2 SnBr 4 /PDA shows the optimal synergy, yielding a high luminescence dissymmetry factor (| g lum |) of 3.5 × 10 −2 , representing a significant enhancement over the pristine L‐(C 18 ‐NH 3 ) 2 SnBr 4 (| g lum | of 7.0 × 10 −3 ). Furthermore, the composite also exhibits a strong nonlinear chiroptical response with a significant dissymmetry factor ( g SHG‐CD ) of 0.503. We further demonstrate the potential applications of these materials in information encryption and flexible polarized‐light applications. This work reveals interfacial chirality transfer and provides a versatile platform for chiral optoelectronic and spintronic materials.