Emergent Circularly Polarized Luminescence from Self-Assembled Chiral-Ligand-Functionalized CsPbBr3 Nanocrystals

Abstract

Chiral surface ligands can impart optical activity to all-inorganic perovskite nanocrystals, but how this affects chiroptical properties of their assemblies remains unclear. Here we show that self-assembly of CsPbBr3 nanocubes synthesized with a small amount of added chiral ligand N-benzylcinchonidinium bromide (BCD-Br) results in measurable circularly polarized luminescence (CPL). BCD-Br-treated nanocrystals show weak circular dichroism but no detectable CPL in colloidal dispersion. Upon assembly into CsPbBr3 and mixed halide superlattices, they exhibit CPL with a luminescence dissymmetry factor, g lum, of (5 ± 2) × 10–3, whereas untreated controls remain near the noise level. Polarization-resolved transient absorption (TA) reveals an extended spin lifetime of hundreds of picoseconds in BCD-Br-treated nanocrystals, while linear-response time-dependent density functional theory (LR-TDDFT) calculations suggest that inter-nanocrystal coupling can enhance the chiroptical response. These results support the idea that ordered nanocrystal assembly can convert weak ligand-induced chirality into an emergent chiroptical response in perovskite nanocrystal solids.