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