One-pot synthesis and chiroptical activity of single Au-atom doped AuAg28 clusters protected by water-soluble chiral monothiol N‑acetyl‑(S)‑penicillamine (S-NAP)

Abstract

Physicochemical properties of atomically precise metal clusters can be modulated by incorporating different metal atoms. In this article, successful one-pot synthesis of single Au-atom doped chiral AuAg₂₈ clusters protected by water-soluble N‑acetyl‑(S)‑penicillamine (=S-NAP) is reported. The reduction of Ag and Au ions at 0 °C in the presence of S-NAP and triphenylphosphine (TPP) using tetramethylammonium borohydride (TMAB) is crucial. Importantly, upon doping of an Au atom to the monometallic Ag₂₉ cluster, which improves the cluster stability, the chiroptical activity or maximum anisotropy factor of the bimetallic AuAg₂₈ cluster is enhanced as compared to that of the monometallic species, which can be due to an increase in the rotatory strength that is probably brought about by the increased contribution of optical transition associated with helically-arranged surface shell layers. Such chiroptical behaviors suggest that the Au dopant position in the bimetallic cluster is not fluxional but rigid. Then the present results will help design some heteroatom-doped silver clusters with excellent chiroptical properties.