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

This work reports a new second-order nonlinear optical (NLO) material [C(NH 2 ) 3 ] 3 C 3 N 3 S 3 (GU 3 TMT), consisting of π-conjugated planar (C 3 N 3 S 3 ) 3- and triangular [C(NH 2 ) 3 ] + groups. Interestingly, GU 3 TMT exhibits a large NLO response (2.0×KH 2 PO 4 ) and moderate birefringence 0.067 at wavelength 550 nm, even though (C 3 N 3 S 3 ) 3- and [C(NH 2 ) 3 ] + do not exhibit the most favorable arrangement in the structure of GU 3 TMT. First-principles calculations suggest that NLO properties mainly originate from the highly π-conjugated (C 3 N 3 S 3 ) 3- rings, and the π-conjugated [C(NH 2 ) 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.