Giant Optical Activity in 2D Hybrid Copper Halides: Novel Material for Second Harmonic Generation

Hybrid organic–inorganic metal halides have emerged as highly promising materials for a wide range of applications in optoelectronics. Incorporating chiral organic molecules into metal halides enables the extension of their unique optical and electronic properties to chiral optics. By using chiral ( R )‐ or ( S )‐methylbenzylamine (R‐/S‐MBA) as the organic component, we synthesized chiral hybrid copper halides, (R‐/S‐MBA) 2 CuCl 4 , and investigated their optical activity. Thin films of this material showed a record anisotropic g‐factor as high as approximately 0.06. We discuss the origin of the giant optical activity observed in (R‐/S‐MBA) 2 CuCl 4 by theoretical modeling based on density functional theory (DFT) and demonstrate highly efficient second harmonic generation (SHG) in these samples. Our study provides insight into the design of chiral materials by structural engineering, creating a new platform for chiral and nonlinear photonic device applications of the chiral hybrid copper halides.