Solvent effect on chiroptical properties of chiral atomically thin CdSe nanoplatelets capped with enantiomeric ligands

Chiral semiconductor nanostructures have growing interest due to applications in enantioselective catalyst and separation, chiral sensing, photonics and spintronics. Here, we have studied solvent effect on the optical and chiroptical properties of atomically thin 2 and 3 monolayers (0.6 and 0.9 nm) thick CdSe nanoplatelets (NPLs) grown by a colloidal method and capped with chiral N-acetyl-l-cysteine ligand. An analysis of the dependence of circular dichroism on the dielectric constants of organic solvents demonstrates an order-of-magnitude increase in the dissymmetry factor for heavy-hole (HH) and light-hole (LH) excitons with a decrease in the dielectric constant of the solvent achieving 2‧10⁻² for the thinnest 2 ML NPLs. It was supplemented by a change in the contributions of HH and LH excitons to the absorption spectra and variation in the spectral position of excitons, which can be explained by the effect of dielectric screening of 2D excitons. Our study demonstrates approaches to control the rotational strength of 2D excitons in chiral semiconductor NPLs simply by changing the surrounding environment, which is important for chiroptical applications.