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

Here we report a 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 large NLO response (2.0 x KH2PO4) and moderate birefringence 0.067 at 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.