Coordination‐Induced Amplification of Birefringence and Nonlinear Optical Response in a Chiral Metal–Organic Framework

Abstract Crystalline materials exhibiting programmable optical anisotropy are of great interest for advanced photonic applications but remain challenging. In this study, we introduce a coordination‐driven approach that significantly enhances optical anisotropy by transforming a loosely packed molecular crystal ( crystal‐1 ) into a chiral metal–organic framework (MOF) ( crystal‐2 ). This structural transformation leads to a more than 20‐fold increase in birefringence (Δ n = 0.226 at 546 nm) and activates a measurable second‐harmonic generation (SHG) activity. First‐principles calculations suggest that the observed optical enhancement is driven by three main factors: coordination‐driven enhancement of asymmetry, alignment of the π‐conjugated framework, and anisotropic electron distribution. These findings highlight the potential of coordination polymerization as a versatile approach for designing hybrid optical materials with tailored anisotropy, providing a foundation for the development of MOF‐based photonic devices.