Krishnadas Kumaranchira Ramankutty, Sementa Luca, Medves Marco, Fortunelli Alessandro, Stener Mauro, Fürstenberg Alexandre, Longhi Giovanna, Bürgi Thomas
Département de Chimie Physique, Université de Genève, 30 Quai Ernest-Ansermet, 1211 Geneva 4, Switzerland.
CNR-ICCOM & IPCF, Consiglio Nazionale delle Ricerche, Via Giuseppe Moruzzi 1, 56124 Pisa, Italy.
ACS Nano. 2020 Aug 25;14(8):9687-9700. doi: 10.1021/acsnano.0c01183. Epub 2020 Jul 29.
We probe the origin of photoluminescence of an atomically precise noble metal cluster, AgAu(DMBT) (DMBT = 2,4-dimethylbenzenethiolate), and the origin of chirality in its chirally functionalized derivatives, AgAu(/-BINAS)(DMBT), with = 1-7 (/-BINAS = /-1,1'-[binaphthalene]-2,2'-dithiol), using chiroptical spectroscopic measurements and density functional theory (DFT) calculations. Combination of chiroptical and luminescence spectroscopies to understand the nature of electronic transitions has not been applied to such molecule-like metal clusters. In order to impart chirality to the achiral AgAu(DMBT) cluster, the chiral ligand, /-BINAS, was incorporated into it. A series of clusters, AgAu(/-BINAS)(DMBT), with = 1-7, were synthesized. We demonstrate that the low-energy electronic transitions undergo an unexpected achiral to chiral and back to achiral transition from pure AgAu(DMBT) to AgAu(/-BINAS)(DMBT), by increasing the number of BINAS ligands. The UV/vis, luminescence, circular dichroism, and circularly polarized luminescence spectroscopic measurements, in conjunction with DFT calculations, suggest that the photoluminescence in AgAu(DMBT) and its chirally functionalized derivatives originates from the transitions involving the whole AgAuS framework and not merely from the icosahedral AgAu core. These results suggest that the chiroptical signatures and photoluminescence in these cluster systems cannot be solely attributed to any one of the structural components, that is, the metal core or the protecting metal-ligand oligomeric units, but rather to their interaction and that the ligand shell plays a crucial role. Our work demonstrates that chiroptical spectroscopic techniques such as circular dichroism and circularly polarized luminescence represent useful tools to understand the nature of electronic transitions in ligand-protected metal clusters and that this approach can be utilized for gaining deeper insights into the structure-property relationships of the electronic transitions of such molecule-like clusters.
我们使用手性光谱测量和密度泛函理论（DFT）计算，探究了原子精确的贵金属簇AgAu(DMBT)（DMBT = 2,4 - 二甲基苯硫醇盐）的光致发光起源，以及其手性官能化衍生物AgAu(/-BINAS)(DMBT)（其中 = 1 - 7，/-BINAS = /-1,1'-[联萘]-2,2'-二硫醇）中的手性起源。将手性光谱和发光光谱相结合以理解电子跃迁的本质，尚未应用于此类分子状金属簇。为了给非手性的AgAu(DMBT)簇赋予手性，将手性配体/-BINAS引入其中。合成了一系列 = 1 - 7的簇AgAu(/-BINAS)(DMBT)。我们证明，通过增加BINAS配体的数量，低能量电子跃迁经历了从纯AgAu(DMBT)到AgAu(/-BINAS)(DMBT)的意想不到的从非手性到手性再回到非手性的转变。紫外/可见、发光、圆二色性和圆偏振发光光谱测量，结合DFT计算，表明AgAu(DMBT)及其手性官能化衍生物中的光致发光起源于涉及整个AgAuS框架的跃迁，而不仅仅来自二十面体AgAu核。这些结果表明，这些簇系统中的手性光谱特征和光致发光不能仅仅归因于任何一个结构组分，即金属核或保护金属 - 配体寡聚单元，而是归因于它们之间的相互作用，并且配体壳层起着关键作用。我们的工作表明，圆二色性和圆偏振发光等手性光谱技术是理解配体保护金属簇中电子跃迁本质的有用工具，并且这种方法可用于更深入地了解此类分子状簇的电子跃迁的结构 - 性质关系。
