Deep-ultraviolet sulfamate halides with halogen-centered secondary building units for enhanced optical anisotropy

The insufficient birefringence of non-π-conjugated optical materials presents a significant challenge for their deep-ultraviolet (DUV) applications. In this work, four DUV sulfamate halide co-crystals, AX(NH3SO3) (A = Rb, Cs; X = Cl, Br), were successfully synthesized through functional chromophore engineering. All four compounds exhibit promising DUV transparent windows, with RbCl(NH3SO3) and CsCl(NH3SO3) demonstrating short DUV cut-off edges below 185 nm. Remarkably, a significant improvement in birefringence, ranging from 0.069 to 0.075, was observed in all four crystals. These values represent the highest birefringence observed for non-π-conjugated DUV optical materials and exhibit optical anisotropy comparable to that of DUV materials containing π-conjugated groups. Theoretical analysis using the real-space atom-cutting method reveals that the [XAm] (X = Cl, Br; A = Rb, Cs) secondary building units (SBUs) contribute significantly to the birefringence. The incorporation of halogen-centered chromophores provides a novel strategy for designing non-π-conjugated DUV materials with enhanced birefringence and phase-matching capabilities.