Synthesis and Chiroptical Properties of Chiral Lead Halide Molecular Clusters

Abstract

Chiral lead halide molecular clusters (MCs) consisting of PbBr₂, neutral achiral butylamine (BTYA), and chiral methylbenzylamine [(R/S)-MBA] with unique chiral optical properties in both the solution and solid states have been synthesized using ligand-assisted reprecipitation and depositing, separately. Ultraviolet–visible (UV–vis) electronic absorption and photoluminescence (PL) spectra show the first electronic absorption band and sharp blue emission band of the chiral MCs that peaked at 404 and 412 nm, respectively, in both solution and films. The emission asymmetry factor |g_lum| of the chiral MCs is 1.04 × 10^–3 in solution and 2.01 × 10^–3 in the film state at room temperature, indicating excellent circularly polarized luminescence (CPL) properties. This pronounced asymmetry is attributed to the chiral transfer from the chiral ligand to the BTYA-capped PbBr₂ framework due to the chiral MBA ligand coordination with Pb²⁺. The samples exhibited excellent ambient stability for over 1 month, primarily due to strong BTYA–PbBr₂ coordination. The MCs maintained their structure and CPL properties in the solid state, which is important for photonic applications.