A Hybrid Antiperovskite with Strong Linear and Second‐Order Nonlinear Optical Responses

Antiperovskites have been studied since the 1980s because of their rich physical and chemical properties, but their linear and second‐order nonlinear optical responses remain largely unknown. Here we report a new polar crystal, Cs 3 Cl(HC 3 N 3 S 3 ) ( I ), which features a quasi‐one‐dimensional antiperovskite structure composed of ClCs 6 polyhedra and A‐site [HC 3 N 3 S 3 ] 2− rings. To our best knowledge, this kind of antiperovskite structure is reported for the first time. Remarkably, I exhibits a very strong nonlinear optical response up to 11.4 times that of the benchmark KH 2 PO 4 and exceptionally large birefringence of 0.52. The first‐principles calculations and structural analyses reveal that [HC 3 N 3 S 3 ] 2− is the “material gene” while the antiperovskite structural feature making it in a favorable arrangement. This work provides a new structural platform for the rational design of integrated optoelectronic materials with linear and second‐order nonlinear optical responses.