Sulfate Derivatives with Heteroleptic Tetrahedra: New Deep‐ultraviolet Birefringent Materials in which Weak Interactions Modulate Functional Module Ordering

Deep‐ultraviolet (UV) birefringent materials are urgently needed to facilitate light polarization in deep‐UV lithography. Maximizing anisotropy by regulating the alignment of functional modules is essential for improving the linear optical performance of birefringent materials. In this work, we proposed a strategy to design deep‐UV birefringent materials that achieve functional module ordering via weak interactions. Following this strategy, four compounds CN4H7SO3CF3, CN4H7SO3CH3, C(NH2)3SO3CH3, and C(NH2)3SO3CF3 were identified as high‐performance candidates for deep‐UV birefringent materials. The millimeter‐sized crystals of CN4H7SO3CF3, CN4H7SO3CH3, and C(NH2)3SO3CH3 were grown, and the transmittance spectra show that their cutoff edges are below 200 nm. CN4H7SO3CF3 exhibits the largest birefringence (0.149 @ 546 nm, 0.395 @ 200 nm) in the deep‐UV region among reported sulfates and sulfate derivatives. It reveals that the hydrogen bond can modulate the module ordering of the heteroleptic tetrahedra and planar π‐conjugated cations, thus greatly enhancing the birefringence. Our study not only discovers new deep‐UV birefringent materials but also provides an upgraded strategy for optimizing optical anisotropy to achieve efficient birefringence.