Spatial Distribution of the Second Harmonic Emission of a Bent Organic Crystal

Abstract As adaptive organic crystals emerge as a new platform for flexible nonlinear optical (NLO) materials, understanding of the relationship between their deformation and their NLO properties is becoming critically important for the design of efficient organic optics. This study reports an organic crystalline compound that integrates a variety of mechanical properties, such as elastic bending, plastic bending, and twisting with strong second‐harmonic generation (SHG). The SHG intensity of the material, a chiral Schiff base, was found to vary across the bent region of its elastically bent crystals, with the intensity of the emission from the inner arc being stronger than that from the outer arc. On the contrary, the SHG intensity distribution in a plastically bent crystal does not appear to follow a regular trend. Density Functional Theory (DFT) calculations point out to the close molecular packing in the elastically bent region as the reason for the enhanced SHG activity of its inner arc. This study not only provides insights into the relationship between crystal deformation and the SHG activity, but it may also lead to approaches for spatial control of nonlinear optical (NLO) properties in flexible organic crystalline materials.