Cs 3 In(In 4 Se 7 )(P 2 Se 6 ): A Multi-Chromophore Chalcogenide with Excellent Nonlinear Optical Property Designed by Group Grafting.

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.