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) [(o‐C5H5NO)2ZnCl2] (1) and [o‐C5H6NO]2[ZnCl4] (2) were obtained by introducing the π‐conjugated o‐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.