Optically Active Au–Cu Bimetallic Nanoclusters: Insights into the Alloying Effect on the Chiroptical Behavior

Inspired by the knowledge that the chiroptical activity of Cu and Ag nanoclusters (NCs) is generally about several-fold larger than that of the corresponding Au NCs but poor stability and that alloy metal particles often demonstrate unique stability, in this contribution the synthesis of the chiral Au–Cu alloy NCs was attempted via reduction of varying mole fractions of metal precursors by sodium borohydride in the presence of d-/l-penicillamine (d-/l-Pen), to gain insights into the alloying effect on the chiroptical activity. As a result, the g factors of ∼0.57 × 10–3, obviously larger than that of the pure Au NCs, are found for the bimetallic Au–Cu NCs, suggesting that the incorporation of Cu heteroatoms plays a dramatic role for the creation of the strong optically active metal nanostructures. More importantly, compared with those of monometallic Cu counterparts, the optical active stability of bimetallic Au–Cu NCs is obviously improved because of the alloy formation. The location of the copper dopant, observed from the transmission electron microscopy results and deduced by the X-ray photoelectron spectroscopy measurements, can be speculated to be incorporated in both the “core” region and the “staple” region. Additionally, it was found that the different thiolated chiral molecule ligands exert influence on the chiroptical behavior of the Au–Cu NCs. Thus, the alloy formation strategy could produce novel nanostructures with the characteristic of large and stable chiroptical activity.