Atom-Response-Theory-Guided Design of Chiral Niobium Halides with both a Large Nonlinear Coefficient and Strong Chiroptical Nonlinearity

Chiral hybrid organic–inorganic metal halides (HOIMHs) with noncentrosymmetric structure have attracted significant attention for nonlinear optics (NLO). Herein, guided by atom response theory (ART), we screened representative lead-free metal halide polyhedra and found that [NbCl 6 ] − exhibits the highest linear polarizability. Therefore, we constructed the first chiral niobium-based HOIMHs, ( R / S -3BrMBA)NbCl 6 ( R / S -Nb ), and investigated their NLO properties. As expected, S -Nb exhibits efficient second harmonic generation (SHG) under 770–1000 nm excitation. Most importantly, the effective second-order NLO coefficient ( d eff ) of S -Nb reaches 6.77 pm/V, representing the highest value among the reported zero-dimensional chiral HOIMHs. Moreover, S -Nb demonstrates strong SHG circular dichroism (SHG-CD) under circularly polarized excitation, with an anisotropy factor ( g SHG-CD ) of 1.37, which is one of the highest values among chiral HOIMHs. Our results highlight the potential of chiral niobium halides toward nonlinear chiroptical applications and provide an effective ART-guided strategy for designing high-performance NLO material through polarizability and band-gap engineering.