Flat-Shaped Copper Nanoclusters with Near-Infrared Absorption for Enhanced Photothermal Conversion

Atomically precise metal nanoclusters have emerged as a prominent area of research in recent years, yet the majority of previous studies have primarily concentrated on gold and silver ones. The challenge of controlling the shape of copper nanoclusters in order to investigate their relationship to properties remains a significant concern in contemporary scientific research. In this study, we successfully achieved shape control of a copper nanocluster with a rare flat oblate structure using a combination of multiple ligands (trifluoroacetic acid, 4-fluorothiophenol, and triphenylphosphine). The resulting nanocluster, with the composition Cu₆₂(4-F-PhS)₃₀(CF₃COO)₈(PPh₃)₆H₁₀, features a flat metal core of aspect ratio as high as 2.6, which is stabilized by ligands attached to or bridged onto the flat kernel. Unlike most previously reported copper nanoclusters, Cu₆₂ exhibits absorption in the near-infrared range. Density functional theory calculations reveal that the main occurrence of near-infrared transitions takes place at the equatorial radius of the Cu₆₂ nanocluster metal core, corresponding to the radial exciton oscillation caused by the confinement of a flattened inner core structure, similar to the plasmon resonance in metal nanoparticles. The unique flattened oblate structure of the nanocluster can also promote the photothermal conversion efficiency (PCE). The temperature of the cluster solution increases from room temperature to around 90 °C in just 10 min, achieving a PCE of approximately 56%. This study not only has the potential to stimulate further research on both the control of copper nanocluster structures and the exploration of their applications but also provides a model system for investigating the relationship between structure and photothermal conversion of copper nanomaterials.