Single-molecule manipulation of copper nanoclusters for modulating nonlinear optics

The molecular-level elucidation of structure-property relationships of metal nanoclusters is quite valuable for further structure design and performance optimization. Nevertheless, the single-molecule manipulation of metal nanoclusters for controlling their physic-chemical properties remains a grand challenge. Herein, we demonstrate that the third-order nonlinear optical (NLO) performance of structurally precise copper nanoclusters can be efficiently modulated by single-molecule chemistry. Two analogous clusters, [Cu₂₅(RS)₁₈H₁₀]³⁻ (Cu₂₅) and [Cu₂₆(RS)₁₈H₁₀(PPh₃)]²⁻ (Cu₂₆, RSH is 2-fluorobenzenethiol), have been attained and structure determined in the work. Both clusters feature a centered cuboctahedron Cu₁₃ core with a similar shell structure, save for the addition of one more PPh₃Cu⁺unit on the Cu₂₆ cluster. Remarkably, the single molecule difference in the structure has essentially altered their properties including optical characteristics and stability. In comparison to Cu₂₅, Cu₂₆ displays better optical limiting activity. Theoretical calculations suggest that the substantial electron transfer from the PPh₃ ligand to the metal core boosts the NLO performance of Cu₂₆. This work not only showcases that structurally precise copper nanoclusters are a promising class of optical limiting (OL) materials but also deepens the understanding of fabricating nanoparticulate materials via the single molecule strategy.