Hydrogen‐Bond‐Driven Metal‐Free Crystal (C 6 H 7 N 2 O)(NH 2 SO 3 ) with Giant Birefringence and Solar‐Blind Ultraviolet Transmission

Abstract Resolving the inherent giant birefringence‐wide bandgap trade‐off constitutes a critical challenge in developing high‐performance birefringent crystals for advanced optical applications. Herein, a strategy based on the coupling of molecular units and hydrogen bond‐directed crystal engineering is proposed to develop a novel metal‐free nicotinamide sulfamate salt (C 6 H 7 N 2 O)(NH 2 SO 3 ), which features a 2D layered structure. Remarkably, (C 6 H 7 N 2 O)(NH 2 SO 3 ) achieves an outstanding birefringence of 0.452@535 nm, along with a short UV cutoff edge of 274 nm. This work not only presents a superior solar‐blind UV birefringent crystal but also establishes a promising design paradigm for simultaneously optimizing giant birefringence and wide bandgap in hydrogen‐bond‐driven organic crystalline systems.