Enhanced Third‐Order Nonlinear Optical Performance in Chiral‐Induced Non‐Planar Covalent Organic Frameworks

Abstract The covalent linkages in covalent organic frameworks (COFs) extend π‐electron delocalization, providing an ideal platform for constructing materials with excellent third‐order nonlinear optical (NLO) properties. However, excessive π‐conjugation within COF planes leads to increased exciton generation, which weakens the NLO response of COFs. In this study, a chiral induction strategy is employed to effectively disrupt the planarity of the COF structure, resulting in chiral non‐planar COFs. The resulting chiral non‐planar R‐TpPz exhibits a significant improvement in NLO performance compared to its planar counterpart, TpPz. Specifically, the third‐order nonlinear absorption coefficient (β_eff) and refractive index (n₂) of R‐TpPz are −126 cm GW⁻¹ and 1.74 × 10⁻³ cm² GW⁻¹, respectively. The improvement of third‐order NLO properties is attributed to the enhanced built‐in electric field and optimized charge transfer pathways caused by the disruption of planarity. This study provides a new approach for the development of high‐performance NLO COF materials.