A Second‐Order Nonlinear Optical Material Consisting of Two π‐Conjugated Groups.

This work reports a new second‐order nonlinear optical (NLO) material [C(NH2)3]3C3N3S3 (GU3TMT), consisting of π‐conjugated planar (C3N3S3)3− and triangular [C(NH2)3]+ groups. Interestingly, GU3TMT exhibits a large NLO response (2.0×KH2PO4) and moderate birefringence 0.067 at wavelength 550 nm, even though (C3N3S3)3− and [C(NH2)3]+ do not exhibit the most favorable arrangement in the structure of GU3TMT. First‐principles calculations suggest that NLO properties mainly originate from the highly π‐conjugated (C3N3S3)3− rings, and the π‐conjugated [C(NH2)3]+ triangles contribute much less to the overall NLO response. This work will inspire new thoughts with in‐depth on the role of π‐conjugated groups in NLO crystals. [ABSTRACT FROM AUTHOR]