Chirality-Induced Second Harmonic Generation in Supramolecular 4-Nitro-D-Phenylalanine Hybrid Crystal

Abstract

The direct correlation between chirality and second-harmonic generation (SHG) remains underexplored in nonlinear optical (NLO) materials. Herein, we report a pair of dextroisomer and enantiomer crystals, 4-nitro-D-phenylalanine nitrate, (D-NPA, P212121) and its racemate rac-4-nitro-phenylalanine nitrate (rac-NPA, P21/c). D-NPA exhibits excellent SHG performance (2.8 × KDP) and a large birefringence (Δnobv. = 0.131), while rac-NPA is SHG inactive. This pair directly demonstrates that the chirality plays a decisive role in the formation of NCS structure and SHG properties. Theoretical calculations indicate that the SHG primarily originates from the benzene rings and nitro groups in the organic component, their contribution rates are 56% and 47% respectively, and the large birefringence is closely related to the parallel alignment of the NO3 -groups.