Second-order nonlinear optical properties of copper-based hybrid organic-inorganic perovskites induced by chiral amines.

Recently, chiral hybrid organic-inorganic perovskites (HOIPs) are drawing wide attention due to their intrinsic noncentrosymmetric structures which result in fascinating properties such as ferroelectronics and second-order nonlinear optics (NLO). However, previous research mainly focused on chiral lead-based halide perovskites ignoring that the toxic Pb element is harmful to humans and the environment. Herein, we successfully synthesized block-like ( R -/ S -NEA) 2 CuCl 4 (NEA = 1-naphthylethylamine) and needle-like ( R -/ S -CYHEA) 6 Cu 3 Cl 12 (CYHEA = 1-cyclohexylethylamine) single crystals, which crystallize in the Sohncke P 2 1 and I 2 space group, respectively. Each pair of chiral perovskite enantiomers shows mirror circular dichroism (CD) signals. The thin films show an efficient second harmonic generation (SHG) response and the NLO coefficients of ( R -NEA) 2 CuCl 4 and ( R -CYHEA) 6 Cu 3 Cl 12 are 11.74 and 3.04 pm V -1 , respectively, under 920 nm excitation with Y-cut quartz as a reference, which shows that the chiral amine has a significant effect on the SHG behavior. The high SHG response of ( R -NEA) 2 CuCl 4 is perhaps due to the rigidity of the aromatic amine, which leads to highly asymmetrical space groups. Our results provide guidelines for designing and tuning the SHG response in chiral HOIPs.