The mechanism of ligand-induced chiral transmission through a top-down selective domain etching process

Abstract

Induced chirality in colloidal semiconductor nanoparticles has received much attention in the past few years as an extremely sensitive spectroscopic tool and because of the promising applications of chiral quantum dots (QDs) in sensing, quantum optics, and spintronics. Yet, the origin of chiroptical effects induced in these nanoparticles is not fully understood, partly because almost all theoretical and experimental studies performed so far are based on the comparison of the g-factor of bulk solutions, which may not truly reflect the variation of the chiral signal in a single nanoparticle. This is because, at a given absorbance value, any change in the molar absorption coefficient at the single nanoparticle level does seriously affect the estimation of the real number of nanoparticles and comparison in-between solutions. Here, we show that using a top-down chemical etching process of colloidal two-component CdSe/CdS dot-in-rods (DRs) nanoparticles can facilitate precise control of nanocrystal solutions with identical concentrations, which cannot be achieved by bottom-up hot injection technology alone. This approach is highly required for studying ligand-induced chiral conduction mechanisms because it effectively eliminates the influence of both the concentrations of nanoparticles and ligands at the same time, instead of relying only on the g-factor related to absorbance. The results showed, thanks to the top-down selective domain etching system, that the shell layer had a negative correlation with the chirality of the first exciton peak (CdSe core contribution), but a positive correlation with the chirality of the CdS shell absorption. At the same time, the core integrity is crucial for DRs to maintain high circular dichroism (CD) and circularly polarized luminescence (CPL) signals. This work, on the one hand, advances the understanding of the fundamental origin of chiral conduction effects induced in semiconductor nanoparticles, and, on the other hand, opens a path to applications using chiral materials.