Regulation of metal valence states for enhancing second harmonic generation performance of chiral tin halides

Chiral metal halide perovskites (MHPs) possess an inherent noncentrosymmetric structure, offering a promising platform for the development of second-order nonlinear optical (NLO) materials. Recent research has emphasized the influence of metal valence states on the physical and chemical properties of perovskites. In this work, a series of novel chiral tin-based MHPs were constructed by adjusting the metal valence states, thereby tuning the second-order NLO performance. Through the oxidation strategy, (<i>R</i>-/<i>S</i>-3-methylpiperidine)₂SnBr₃Br (R-/S-2Sn) can be easily transformed into centimeter-scale (<i>R</i>-/<i>S</i>-3-methylpiperidine)₂SnBr₆ (R-/S-4Sn) crystals. This transformation significantly enhances the second harmonic generation (SHG) response owing to the reduction in crystal spatial symmetry following the change in the valence states of tin. This work highlighted the potential of low-dimensional chiral tin-based MHPs in high-performance NLO applications, offering a foundation for future exploration in this field.