Breaking Boundaries: Giant Ultraviolet Birefringence in Dimension‐Reduced Zn‐Based Crystals

Birefringent crystals have essential applications in optical communication areas. Low-dimensional structures with inherited structural anisotropy are potential systems for investigating birefringent materials with large birefringence. In this work, the zero-dimensional (0D) [(p-C₅H₅NO)₂ZnCl₂] (1) and [p-C₅H₆NO]₂[ZnCl₄] (2) were obtained by introducing the π-conjugated p-C₅H₅NO (4HP) into the three-dimensional (3D) ZnCl₂. Remarkably, 1 exhibits a giant birefringence of 0.482@546 nm, which is the largest among Zn-based ultraviolet (UV) compounds and 160 times that of ZnCl₂. According to structural and theoretical calculation analyses, the large optical polarizability, high spatial density, ideal distribution of the [(4HP)₂ZnCl₂]⁰ cluster, and the low dimension of 1 result in the dramatically increased birefringence compared to ZnCl₂. This work will provide a valid route for accelerating the design and synthesis of compounds with excellent birefringence in low-dimensional systems.