Ligand Effects on Luminescence of Atomically Precise Gold Nanoclusters

Great efforts have been made to establish the structure-property relationships of ligand-protected metal nanoclusters. An alkynyl-protected gold nanocluster Au₂₈(^<i>t</i>BuC₆H₄C≡C)₂₀ (<b>Au</b>_<b>28</b><b>-C</b>_<b>2</b>) was synthesized and structurally characterized. It has an isostructural metal kernel and a quite similar ligand shell to its counterpart Au₂₈(^<i>t</i>BuC₆H₄S)₂₀ (<b>Au</b>_<b>28</b><b>-S</b>), which provides a valuable platform for studying ligand effects on the luminescence of clusters. The emission intensity of <b>Au</b>_<b>28</b><b>-C</b>_<b>2</b> in solution is ∼10-fold that of <b>Au</b>_<b>28</b><b>-S</b>. The only structural difference between these two clusters is the donor atom or group, i.e., C≡C for <b>Au</b>_<b>28</b><b>-C</b>_<b>2</b> versus S for <b>Au</b>_<b>28</b><b>-S</b>. Temperature-dependent experiments indicate that the two Au₂₈ clusters have different thermodynamic behaviors and radiative processes. The study on the excited-state dynamics by transient absorption spectroscopy indicates that <b>Au</b>_<b>28</b><b>-C</b>_<b>2</b> has a larger triplet-state population than <b>Au</b>_<b>28</b><b>-S</b>. This work shows important ligand effects on the emission properties of metal nanoclusters, which provide new perspectives for the designed synthesis of functional metal nanoclusters.