The effect of distant substitution patterns present in novel 3-mercaptopropionic acid-based ligands on the structure and optical properties of gold nanoclusters.

This work highlights the effect of substitution patterns present in capping ligands that are away from the binding site on the structure and properties of gold nanoclusters (AuNCs). As the capping ligands are known to influence the properties of AuNCs, studies in this direction are required to explore and enhance the vast potential offered by nanoclusters. However, only a handful of ligands have been systematically used to date to study this correlation. Additionally, in the majority of these studies, even when using similar/isomeric ligands, the synthesized AuNCs were found to have different compositions and structures, making it difficult to draw a straightforward conclusion about the role of ligands in the properties of AuNCs. Emphasizing this aspect, we synthesized three ligands based on 3-mercaptopropionic acid. The ligand structure was varied by the incorporation of electron-donating groups at positions distant from the binding site. The three AuNCs synthesized using these ligands were characterized with the help of UV-vis spectroscopy, FTIR spectroscopy, fluorescence spectroscopy, XPS, MALDI-TOF mass spectrometry and TGA. Interestingly, all three AuNCs synthesized had similar dominant stoichiometric distributions, which indicated that any change in their properties must be due to the effect of the substitution patterns of the ligands. This allowed us to precisely compare the role of ligands on the optical properties of AuNCs. The clusters were found to be weakly fluorescent in the blue region. We observed that the fluorescence quantum yield and lifetimes of the nanoclusters increased with the electron-donating ability of the substituents.