Ligand exchange reactions have become a highly versatile post-synthetic strategy to accurately engineer the ligand shell of atomically precise noble metal nanoclusters. Modifying the chemical structure of the exchanging ligand with chromophore substituents or adding chiral centers allow direct functionalization of the cluster with desired properties. As such, post-functionalized gold nanoclusters with unique physicochemical properties find applications in optoelectronics, catalysis and biomedicine. Herein, we successfully carried out ligand exchange reactions between the chiral Au₃₈(2-PET)₂₄ cluster (both racemic and enantiopure forms) and the helically chiral but configurationally labile 2-thio[4]helicene ligand (TH4). The reaction products with a composition of Au₃₈(2-PET)_24−x(TH4)_x were analyzed using UV-vis spectroscopy and MALDI mass spectrometry. It was found that up to ten 2-PET ligands can be replaced with the helicene ligand on the cluster surface according to MALDI analysis. Consequently, the UV-vis and CD spectra of the cluster have been strongly affected by the ligand exchange reaction. The intensities of the CD signals of Au₃₈(2-PET)_24−x(TH4)_x were drastically reduced and red shifted with respect to the reference Au₃₈(2-PET)₂₄ cluster. Moreover, the appearance of the other enantiomer in the HPLC chromatogram revealed the partial racemization of the cluster. DFT calculations were performed and they support the experimental observations and show that the observed chiroptical changes in UV-vis and CD spectra are exchange-site dependent. The calculations also demonstrate that charge transfer (CT) transitions occur between the Au₃₈ cluster and the helicene ligand. Thus the ligand is directly involved in these transitions and contributes to the electronic states comprising those transitions.

中文翻译：

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手性Au38簇上的配体交换反应：CD调节，是由配体壳组成的修饰引起的。

配体交换反应已成为一种高度通用的合成后策略，可以精确地设计原子精确的贵金属纳米簇的配体壳。用生色团取代基修饰交换配体的化学结构或添加手性中心，可以使簇直接官能化并具有所需的特性。因此，具有独特的物理化学性质的后功能化金纳米簇可用于光电，催化和生物医学。在这里，我们成功地进行了手性金₃₈（2-PET）₂₄簇（外消旋和对映纯形式）和螺旋手性但构型不稳定的2-硫代[4]螺旋烯配体（TH4）之间的配体交换反应。Au ₃₈组成的反应产物（2-PET）₂₄ - _x（TH4）_x使用紫外可见光谱和MALDI质谱分析。根据MALDI分析，发现簇表面上的多达十个2-PET配体可以被螺旋烯配体代替。因此，该簇的UV-vis和CD光谱受到配体交换反应的强烈影响。Au ₃₈（2-PET）_{24- x}（TH4）_x的CD信号强度相对于参考Au ₃₈（2-PET）₂₄显着降低并发生红移簇。此外，HPLC色谱图中其他对映异构体的出现表明簇的部分消旋。进行了DFT计算，它们支持实验观察，并表明观察到的紫外-可见光谱和CD光谱的手性变化取决于交换位点。该计算还表明，在Au ₃₈簇和螺旋烯配体之间发生了电荷转移（CT）跃迁。因此，配体直接参与这些转变，并有助于构成这些转变的电子态。