Ligand substitution in organic–inorganic hybrid zinc iodides for second-harmonic generation

Abstract

Noncentrosymmetric metal halides are promising nonlinear optical (NLO) materials that have prospective applications in optical switching technologies. However, obtaining zinc halides with large second harmonic generation (SHG) effect is of great challenge due to their ideal tetrahedral configurations. In this study, four organicinorganic hybrid zinc iodides, namely, (HIm)2[ZnI4]·H2O (1), (HIm)[ZnI3(Im)] (2), ZnI2(Im)2 (3), and [ZnI(Im)3]I (4) have been synthesized by a ligand substitution approach, where Im = imidazole. Structural analysis shows that compound 2 is noncentrosymmetric, while the remaining three compounds are centrosymmetric. Notably, compound 2 exhibits a strong SHG response of 4.0 times that of KH2PO4 under 1064 nm laser irradiation. Theoretical studies indicate that the SHG activity of compound 2 is attributed to the synergistic effect of the distorted zinc-centered tetrahedra and π-conjugated organic components. This research sheds new light on the development of zinc halide NLO materials through ligand engineering.