Seuret-Hernández Halis Yenis, Gamboa-Suaréz Antonio, Morera-Boado Cercis
Centro de Investigaciones Químicas, IICBA, Universidad Autónoma Del Estado de Morelos, Cuernavaca, 62209, Morelos, Mexico.
Cátedra Conacyt-Centro de Investigaciones Químicas, IICBA, Universidad Autónoma Del Estado de Morelos, Cuernavaca, 62209, Morelos, Mexico.
J Mol Graph Model. 2022 Sep;115:108234. doi: 10.1016/j.jmgm.2022.108234. Epub 2022 May 29.
This work presents a theoretical detailed analysis of the surface-enhanced Raman spectroscopy (SERS) of the pyridine - Au, pyridine - Ag and pyridine - AgAu model systems considering different symmetries of the clusters. In addition to the well-known Td geometry of this twenty atoms metal cluster, low energy structures have been analyzed (Cs and Cb). Density functional methodology with the use of PBE, PBE0, and scalar - relativistic pseudopotentials have been employed for the electronic structure calculations of these molecule-metal complexes. The projected state density analysis has shown a different behavior that distinguishes vertex (V) pyridine position from surface (S) adsorption site on both Td and Cs geometries. Adsorption of pyridine on the V position is always energetically favored as compared to S substitution. The chemical mechanism of enhancement has been analyzed through charge-transfer in the adsorption of pyridine to the metal cluster and charge-transfer excitations between both moieties. There is a close relationship between the amount of charge transfer from the pyridine molecule to the cluster and the SERS enhancements. The highest enhancement factors were obtained precisely for the Au cubic structure, where 10 order enhancements were calculated. A back - donation of charge triggers the highest enhancements obtained for this case. The bimetallic case also shows an improvement in the enhancements as compared to Td and Cs geometries. In addition, a direct relationship between resonant charge - transfer excitations in the 500-530 nm range and SERS enhancement have been obtained. Cs and cubic clusters show higher chemical enhancements than Td structures, thus representing a promise as SERS substrates.
这项工作对吡啶-Au、吡啶-Ag和吡啶-AgAu模型系统的表面增强拉曼光谱（SERS）进行了理论上的详细分析，考虑了团簇的不同对称性。除了这种二十原子金属团簇众所周知的Td几何结构外，还分析了低能量结构（Cs和Cb）。采用了使用PBE、PBE0和标量相对论赝势的密度泛函方法对这些分子-金属配合物进行电子结构计算。投影态密度分析显示了不同的行为，这区分了Td和Cs几何结构上顶点（V）吡啶位置与表面（S）吸附位点。与S取代相比，吡啶在V位置的吸附在能量上总是更有利。通过吡啶吸附到金属团簇时的电荷转移以及两个部分之间的电荷转移激发，分析了增强的化学机制。从吡啶分子到团簇的电荷转移量与SERS增强之间存在密切关系。精确地对于Au立方结构获得了最高的增强因子，其中计算出了10个数量级的增强。电荷的反向捐赠引发了这种情况下获得的最高增强。与Td和Cs几何结构相比，双金属情况也显示出增强的改善。此外，在500-530nm范围内的共振电荷转移激发与SERS增强之间获得了直接关系。Cs和立方团簇显示出比Td结构更高的化学增强，因此作为SERS基底具有前景。
