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.