A[N(SO2NH2)2] (A=Na, K, Rb, and Cs): Enhancing Birefringence of Non π-Conjugated Deep-Ultraviolet Crystals via Novel Dimeric Disulfonamide [N(SO2NH2)2]⁻ Groups

Abstract

Achieving high optical anisotropy in deep-ultraviolet (DUV) crystals built from conventional non-π-conjugated tetrahedral units has long been a major challenge. Extending beyond the tetrahedral hetero-coordination substitution strategy, we introduce a base-induced dehydrogenative condensation approach that affords a novel dimeric disulfonamide [N(SO2NH2)2]⁻ unit. Using this outstanding functional unit, four alkali metal crystals A[N(SO2NH2)2] (A=Na, K, Rb, and Cs) were obtained, which all exhibited DUV transmission capability with cutoff edges below 190 nm and notable birefringence of 0.056~0.066@546 nm. Interestingly, this unit can adopt cis and trans conformations, which can offer structural flexibility and diversity for crystal design. This work highlights [N(SO2NH2)2]⁻ as a new promising functional motif for DUV birefringent and other optical crystals, while offering new insights into their rational design.