Confinement π‐Conjugated Moiety Tailoring to Achieve Record Deep‐UV Nonlinearity in Sulfates

The development of deep ultraviolet nonlinear optical (DUV NLO) materials with simultaneous high performance across multiple properties remains a significant challenge. Key properties, such as a short UV cutoff edge, strong second‐harmonic generation (SHG) response, and suitable birefringence, are often mutually constrained. This study introduces a novel “Three Birds with One Stone” strategy, utilizing a confined π‐conjugated functional group, [OOCCH(NH 3 )CH 2 SO 3 ] − , integrated into the sulfate framework. The approach enhances both polarizability anisotropy and hyperpolarizability while preserving the large band gap inherent to sulfates. This strategy achieves a breakthrough in balancing key performance metrics. Using this new design, we successfully synthesized a novel DUV NLO sulfonate, Li[OOCCH(NH 3 )CH 2 SO 3 ] (LCNS), which demonstrates excellent optical properties, including a short UV cutoff edge (177 nm), a record SHG response (4.5 × KDP), and exceptional birefringence (0.090@589 nm) among DUV NLO sulfonates. This work not only provides a promising candidate for DUV NLO applications but also introduces an innovative strategy for the development of advanced DUV NLO materials.