Bismuth-Based Chiral Perovskite with Different Dimensions for Second-Order Nonlinear Optical Properties

Chiral perovskites have various applications in nonlinear optics due to their asymmetric structures. Currently, nonlinear optical studies have focused on lead-based perovskite. However, the toxic element, Pb, hinders their further applications. Herein, (R/S-MBA)(4)Bi2Br10 (MBA = alpha-phenylethylamine) and (R/S-MPA)(2)BiBr5 (MPA = 1-phenylpropan-1-amine) crystals were synthesized and explored about the nonlinear optics. Both pairs of chiral perovskite enantiomers exhibit good thermal stability and symmetric circular dichroism signals. Interestingly, MPA and MBA differ by only one methylene but show significant differences in the crystal structures synthesized under the same conditions. The (R/S-MBA)(4)Bi2Br10 crystal is a zero-dimensional (0D) structure in which the [Bi2Br10](4-) dimer is spaced by an organic amine. (R/S-MPA)(2)BiBr5 crystals are 1D structures in which [BiBr6](2-) units form infinitely extended chains by angle sharing. The crystals exhibit efficient second harmonic generation response, and the intensity of (R-MPA)(2)BiBr5 is four times that of (R-MBA)(4)Bi2Br10 at 980 nm excitation wavelength. The 1D infinitely extended inorganic chain in (R-MPA)(2)BiBr5 allows for a more regular arrangement of chiral organic amines, and adjacent organic amines are arranged differently, together leading to its stronger non-centrosymmetry, which is the decisive factor of nonlinear optics. The study guides the design and deep research of novel second-order nonlinear optical materials.