Cadmium sulfide quantum dots functionalized with serine, proline, and aspartic acid homologs to study the influence of ligand size on the induced circular dichroism

Abstract

Chirality, a fundamental property of molecules and materials, underlies numerous critical chemical, biochemical, and optical phenomena. Chiral organic molecules, termed capping ligands, have been shown to induce chirality in intrinsically achiral nanomaterials through electronic and structural interactions, as evidenced by the emergence of a circular dichroic (CD) signal. The sign and intensity of the CD spectra have been demonstrated to reflect both the ligand's absolute configuration and its binding geometry that could be tuned by solvent, temperature, base, countercation, and ligand's concentration. To gain a deeper understanding of ligand-induced chirality and facilitate the rational design of chiral materials, it is crucial to investigate the interplay between molecules and nanomaterials at the solid–liquid interface. In this study, we investigate the influence of capping ligand size on the induced CD spectra of colloidal cadmium sulfide quantum dots (CdS QDs) by using homologous pairs of amino acids: serine-homoserine, proline-homoproline, and aspartic-glutamic acids. In parallel, we explore the impact of a third functional group (attached to the achiral carbon) and the distance between the anchoring carboxylate group and this third functional group using spectroscopic techniques. Our findings highlight the significant role of ligand molecular structure and footprint (steric demand) on the induced CD signal of semiconductor nanoparticles. This study further emphasizes the importance of circular dichroism spectroscopy in probing surface binding geometry, ligand surface orientation, and ligand-nanocrystal hybridization.