Hydrogen bonding regulation-oriented design of pyridine sulfonate as a promising UV birefringent crystal...

Birefringent materials, capable of manipulating light polarization, are pivotal in advanced optical technologies. Traditionally, the development of such materials has predominantly focused on purely inorganic compounds, which often exhibit limited birefringence. Herein, we present a new 3-pyridinesulfonate birefringent crystal, Ca(3-C₅H₄NSO₃)₂·4H₂O, synthesized via a hydrogen-bonded regulation strategy designed to enhance the coplanarity of [3-pySO₃] groups. As expected, Ca(3-C₅H₄NSO₃)₂·4H₂O demonstrates a notably large birefringence of 0.286@532 nm, exceeding that of most commercially available birefringent crystals. Furthermore, this compound demonstrates outstanding environmental stability and a short ultraviolet (UV) absorption cutoff edge at 257 nm, accompanied by a wide band gap of 4.4 eV. A combination of structural analysis and theoretical calculations unraveled the crucial role of hydrogen bonds in optimizing the arrangement of [3-pySO₃] rings. This arrangement effectively induces a high degree of coplanarity and facilitates the formation of a quasi-2D layered structure, thereby contributing to the exceptional optical anisotropy of Ca(3-C₅H₄NSO₃)₂·4H₂O. These findings highlight Ca(3-C₅H₄NSO₃)₂·4H₂O as a promising UV birefringent crystal and underscore the efficacy of hydrogen bond engineering for designing new materials with enhanced birefringent properties.