Chiral Supramolecular Templating Enables Tunable Second-Harmonic Generation in Hybrid Zinc Thiocyanates

초록

Chiral organic molecules have been widely used to construct hybrid nonlinear optical (NLO) materials with second-harmonic generation (SHG) activity. However, the limited diversity of chiral building blocks has restricted both structural diversity and SHG performance. Herein, we introduce a chiral supramolecular templating strategy for engineering hybrid zinc thiocyanates with tunable SHG responses. Alkali or alkaline-earth metal ions and natural amino acids cooperatively assemble into one-dimensional (1D) chiral coordination polymers that serve as supramolecular templates, while the hard-soft acid-base principle suppresses undesired coordination between amino acid ligands and zinc ions. This coordination orthogonality enables different chiral supramolecular templates to direct the spatial organization of the SHG-active [Zn(SCN)4]2- units. The resulting hybrid solids combine wide optical bandgaps, phase-matchable birefringence, and diverse SHG responses. Notably, [K2(L-ser)][Zn(SCN)4] exhibits an SHG intensity of 8.0 & times; KH2PO4, representing the strongest response reported to date for homochiral zinc-based materials derived from natural amino acids. Theoretical analyses reveal that the [Zn(SCN)4]2- units dominate the SHG response, establishing chiral supramolecular templating as a general strategy for designing high-performance hybrid NLO materials.

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