Y(C6H5SO3)3·9H2O: strategic integration of ligand substitution and π-conjugated group linkage in sulfates for enhanced ultraviolet nonlinear optical properties

Ultraviolet (UV) nonlinear optical (NLO) materials are critical for laser frequency conversion to extend wavelength ranges. Sulfates have emerged as a promising family of UV NLO materials, yet their NLO performance is constrained by the low optical anisotropy of the constituent [SO4]2− groups. In this study, we investigate the [C6H5SO3]− group, formed by substituting a ligand of the non-π-conjugated [SO4]2− unit with a π-conjugated benzene ring, and demonstrate that this group has a strong second harmonic generation (SHG) response and large birefringence. Leveraging this optimized structural unit, we successfully synthesize the first UV NLO benzenesulfonate, Y(C6H5SO3)3·9H2O. This compound exhibits enhanced UV optical properties, including a short cutoff edge of 280 nm, a relatively large SHG efficiency (0.8 × KDP), and a large birefringence of 0.16 at 1064 nm. This work not only presents Y(C6H5SO3)3·9H2O as a competitive UV NLO material, but also highlights the [C6H5SO3]− group as a highly effective structural motif for the future development of advanced UV NLO materials.