Simultaneous Boosting of Second Harmonic Generation and Circularly Polarized Luminescence in Chiral Hybrid Metal Halides Through Enhanced Octahedral Distortion

Chiral hybrid metal halides (HMHs), characterized by their non-centrosymmetric crystal structures and exceptional photophysical properties, are promising for second-order nonlinear and linear optics, including second-harmonic generation (SHG) and circularly polarized luminescence (CPL). However, chiral HMHs with simultaneously strong SHG response and efficient CPL still present a challenge, due to the distinct structural and electronic requirements of these properties. Here, we report a halogen substitution strategy within inorganic octahedra to modulate the crystal structure and simultaneously enhance both SHG and CPL properties. Three pairs of chiral Sb-based HMHs are synthesized: (R/S-MBA)₂IASbBr₆ (MBA = α-methylbenzylammonium, IA = imidazole, abbreviated as R/S-SbBr₆), (R/S-MBA)₂IASbBr_2.8Cl_3.2 (R/S-SbBr_2.8Cl_3.2), and (R/S-MBA)₂IASbCl₆ (R/S-SbCl₆). The gradual halogen substitution from R/S-SbBr₆ to R/S-SbCl₆ significantly enhances the structural chirality of inorganic octahedra, resulting in a strong SHG response intensity of 1.4 × KDP and a high luminescence dissymmetry factor of 3.82 × 10^-2. The combination of SHG and CPL performance outperforms that of previous chiral HMHs. Experimental results and theoretical calculations indicate that these enhancements originate from gradually increased octahedral distortions induced by halogen substitution. This work establishes a structural optimization strategy for advancing high-performance SHG and CPL in chiral HMHs, paving the way for their broader photonic applications.