[CON<sub>3</sub>H<sub>6</sub>BF<sub>4</sub>]: An Efficient Metal‐Free Borate with Optimized Birefringence Achieved by Structural Design Strategy
Muhammad Arif, Xu Liu, Hangwei Jia, Zhihua Yang, Xueling Hou, Shilie Pan
Abstract
Abstract Deep‐ultraviolet (UV) birefringent materials are urgently needed for advancing light polarization in deep‐UV lithography. In crystal engineering, maximizing anisotropy by classical template alteration demonstrates its efficiency in achieving superior performance characteristics. Consequently, a novel planar deep‐UV functional building unit (FBU), [CON 3 H 5 ], is proposed, acquired by amino modulation within the urea template. This article presents a methodical investigation of novel fluoroborate [(CON 3 H 6 )BF 4 ] (AUBF), designed by unifying a planar π ‐conjugated functional cation with a fully fluorinated non‐ π ‐conjugated tetrahedron in a single system. The compound exhibits well‐balanced properties, owing to its parallel molecular arrangement, and has been characterized as a high‐performing deep‐UV birefringent material. As is known to all, it is the first semi‐organic urea‐based compound to reach the deep‐UV region with a cutoff edge at 196 nm, and a substantial birefringence of 0.127@546 nm, similar to that of the previously reported urea‐based compounds as well as commercial birefringent crystal α ‐BBO (0.123@546 nm). This work not only identifies a novel birefringent gene with improved optical anisotropy but also opens the door for synthesizing novel deep‐UV birefringent materials via a structural regulation design strategy.