State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, PR China.
Nanoscale. 2018 Sep 13;10(35):16787-16794. doi: 10.1039/c8nr05253k.
We have synthesized Ag12 nanoclusters (NCs) with mercaptosuccinic acid (H2SMA) as the ligand. This cluster is found to be water-soluble and has satisfactory stability with [Ag12(HSMA)6Na6]2+, as determined by high-resolution mass spectrometry. Interestingly, it is noted that both the H2SMA ligand and Ag12 clusters do not display interference Raman signals, suggesting that this material is a good candidate as a substrate for surface-enhanced Raman spectroscopy (SERS). As a result, we observe enhanced Raman activity of pyrazine molecules adsorbed on Ag12 NCs along with a large red-shift up to ∼27 cm-1. To fully demonstrate the charge transfer interactions between pyrazine and Ag12 clusters, by utilizing first-principles calculations, we estimate polarizability tensor and conduct electronic natural population analysis (NPA), natural bond orbital (NBO) analysis, deformation density analysis (DDA) and charge decomposition analysis (CDA). In view of the minimized contribution from local surface plasmon resonance (LSPR), such a comprehensive study of metal NCs, which are free of Raman interference, provides a modelling method towards the long-debated chemical mechanism in SERS theory.
我们合成了以巯基琥珀酸（H2SMA）作为配体的 Ag12 纳米团簇（NCs）。高分辨率质谱表明，该团簇具有水溶性和令人满意的稳定性，为 [Ag12(HSMA)6Na6]2+。有趣的是，我们注意到 H2SMA 配体和 Ag12 团簇都没有显示出干扰拉曼信号，这表明该材料是表面增强拉曼光谱（SERS）的一个很好的候选基底。因此，我们观察到吸附在 Ag12 NCs 上的吡嗪分子的增强拉曼活性，同时观察到高达约 27 cm-1 的大红移。为了充分证明吡嗪与 Ag12 团簇之间的电荷转移相互作用，我们利用第一性原理计算来估计极化张量并进行电子自然布居分析（NPA）、自然键轨道（NBO）分析、变形密度分析（DDA）和电荷分解分析（CDA）。考虑到局部表面等离子体共振（LSPR）的最小贡献，这种对无拉曼干扰的金属 NCs 的综合研究为 SERS 理论中长期争论的化学机制提供了一种建模方法。
