Circular dichroism and circularly polarized luminescence of ligand-protected molecular metal clusters: insights into structure-chiroptical property relationships.

Molecular noble metal clusters are an emerging class of circularly polarized luminescent (CPL) nanomaterials. Many of the ligand-protected metal clusters exhibit discrete electronic absorption bands, which are assigned to their structural components such as metal core, ligands and metal-ligand interfaces. This implies the suitability of the chiroptical spectroscopic approach to unravel the structure-chiroptical property relationships in molecular metal clusters. Due to the tremendous developments in computational methods for investigating chiroptical properties, along with circular dichroism (CD) and CPL spectroscopy, understanding of the structure-chiroptical properties of these clusters is rapidly progressing. This review discusses various strategies such as the use of chiral ligands, metal atom substitution, ligand exchange, co-crystallization with chiral ligands, ., for inducing and enhancing the CPL of such metal clusters. This review demonstrates the potential of combined CD-CPL spectroscopic investigations and theoretical calculations to unravel the origins of photoluminescence and CPL activity of chiral metal clusters.