Cs3In(In4Se7)(P2Se6): A Multi‐Chromophore Chalcogenide with Excellent Nonlinear Optical Property Designed by Group Grafting

Abstract Non‐centrosymmetric (NCS) and polar materials capable of exhibiting many important functional properties are indispensable for electro‐optical technologies, yet their rational structural design remains a significant challenge. Here, we report a “group grafting” strategy for designing the first multi‐chromophore selenophosphate, Cs 3 In(In 4 Se 7 )(P 2 Se 6 ), that crystallizes in a NCS and polar space group of Cm . The structure features a unique basic building unit (BBU) [In(In 4 Se 10 )(P 2 Se 6 )], formed through “grafting [In 4 Se 10 ] supertetrahedra on the root of [In(P 2 Se 6 ) 2 ] groups”. Theoretical calculations confirm that this [In(In 4 Se 10 )(P 2 Se 6 )] BBU can achieve a “1+1>2” combination of properties from two chromophores, [In 4 Se 10 ] supertetrahedron and ethane‐like [P 2 Se 6 ] dimer. That makes Cs 3 In(In 4 Se 7 )(P 2 Se 6 ) exhibit excellent linear and nonlinear optical (NLO) properties, including a strong second harmonic generation (SHG) response (~6×AgGaS 2 ), a large band gap (2.45 eV), broad infrared (IR) transmission (up to 19.5 μm), a significant birefringence (0.26 @1064 nm) as well as the congruently‐melting property at ~700 °C. Therefore, Cs 3 In(In 4 Se 7 )(P 2 Se 6 ) will be a promising NLO crystal, especially in the IR region, and this research also demonstrates that “group grafting” will be an effective strategy for constructing novel polar BBUs with multi‐chromophore to design NCS structures and high‐performance IR NLO materials.