Electronic Structures and Photoluminescence of Monolayer-Protected Metal Clusters

我们开发了一种化学成分明确的硫代酸保护金簇的合成方法。该方法基于聚丙烯酰胺凝胶电泳（PAGE）、凝胶渗透色谱（GPC）和质谱表征的粒度分离。利用各种光谱方法和理论计算对合成的硫代金（Au: SR）簇的电子结构和几何结构进行了研究。研究结果总结如下。1)相应Au(I)-SR聚合物还原形成的Au: SR团簇与生长团簇的捕获中间体相对应。我们观察到几个神奇编号的金团簇，如Au25(SG)18和Au55(SC18)32，其中GSH和C18SH分别代表谷胱甘肽和十八烷硫醇。2)小Au: SR团簇的光致发光量子产率为10^<-3>- 10^<-4>，明显大于大块金团簇的量子产率（10^<-10>）。这种增强可归因于准分子电子结构。无论核心大小如何，发射波长几乎是恒定的。这表明PL来源于附着在金团簇表面的Au-SR环结构。该结构模型得到了理论研究的支持。

We have developed a synthetic method of thiolate-protected gold clusters with well-defined chemical compositions. The method is based on size separation by using polyacrylamide gel electrophoresis (PAGE) and gel permeation chromatography (GPC) and mass spectrometric characterization. Electronic and geometrical structures of the thiolated gold (Au : SR) clusters thus synthesized were studied by using various spectroscopic methods and theoretical calculations. The findings are summarized as follows.1)The Au : SR clusters formed by reduction of the corresponding Au(I)-SR polymer correspond to trapped intermediates of the growing clusters. We observed several magic-numbered gold clusters such as Au25(SG)18 and Au55(SC18)32, where GSH and C18SH represent glutathione and octadecanethiol, respectively.2)The small Au : SR clusters exhibit photoluminescence with quantum yield of 10^<-3>- 10^<-4>, which is significantly larger than that of bulk gold (10^<-10>). This enhancement is attributable to the quasi-molecular electronic structures. The emission wavelengths are nearly constant irrespective of the core size. This suggests that the PL originates from the Au-SR ring structures attached on the gold cluster surface. This structure model is supported by theoretical studies.