Schürmann Robin, Nagel Alessandro, Juergensen Sabrina, Pathak Anisha, Reich Stephanie, Pacholski Claudia, Bald Ilko
Institute of Chemistry, University of Potsdam, D-14476 Potsdam, Germany.
Department of Physics, Freie Universität Berlin, D-14195 Berlin, Germany.
J Phys Chem C Nanomater Interfaces. 2022 Mar 24;126(11):5333-5342. doi: 10.1021/acs.jpcc.2c00278. Epub 2022 Mar 15.
Surface-enhanced Raman scattering (SERS) is an effective and widely used technique to study chemical reactions induced or catalyzed by plasmonic substrates, since the experimental setup allows us to trigger and track the reaction simultaneously and identify the products. However, on substrates with plasmonic hotspots, the total signal mainly originates from these nanoscopic volumes with high reactivity and the information about the overall consumption remains obscure in SERS measurements. This has important implications; for example, the apparent reaction order in SERS measurements does not correlate with the real reaction order, whereas the apparent reaction rates are proportional to the real reaction rates as demonstrated by finite-difference time-domain (FDTD) simulations. We determined the electric field enhancement distribution of a gold nanoparticle (AuNP) monolayer and calculated the SERS intensities in light-driven reactions in an adsorbed self-assembled molecular monolayer on the AuNP surface. Accordingly, even if a high conversion is observed in SERS due to the high reactivity in the hotspots, most of the adsorbed molecules on the AuNP surface remain unreacted. The theoretical findings are compared with the hot-electron-induced dehalogenation of 4-bromothiophenol, indicating a time dependency of the hot-carrier concentration in plasmon-mediated reactions. To fit the kinetics of plasmon-mediated reactions in plasmonic hotspots, fractal-like kinetics are well suited to account for the inhomogeneity of reactive sites on the substrates, whereas also modified standard kinetics model allows equally well fits. The outcomes of this study are on the one hand essential to derive a mechanistic understanding of reactions on plasmonic substrates by SERS measurements and on the other hand to drive plasmonic reactions with high local precision and facilitate the engineering of chemistry on a nanoscale.
表面增强拉曼散射（SERS）是一种有效且广泛应用的技术，用于研究由等离子体基底诱导或催化的化学反应，因为该实验装置使我们能够同时触发和跟踪反应并识别产物。然而，在具有等离子体热点的基底上，总信号主要源自这些具有高反应活性的纳米级体积，而在SERS测量中关于整体消耗的信息仍然模糊不清。这具有重要意义；例如，SERS测量中的表观反应级数与实际反应级数不相关，而有限时域差分（FDTD）模拟表明表观反应速率与实际反应速率成正比。我们确定了金纳米颗粒（AuNP）单层的电场增强分布，并计算了AuNP表面吸附的自组装分子单层中光驱动反应的SERS强度。因此，即使由于热点处的高反应活性在SERS中观察到高转化率，AuNP表面上的大多数吸附分子仍未反应。将理论结果与4-溴硫酚的热电子诱导脱卤反应进行比较，表明等离子体介导反应中热载流子浓度具有时间依赖性。为了拟合等离子体热点中等离子体介导反应的动力学，类分形动力学非常适合解释基底上反应位点的不均匀性，而改进的标准动力学模型也能同样很好地拟合。这项研究的结果一方面对于通过SERS测量从机理上理解等离子体基底上的反应至关重要，另一方面对于以高局部精度驱动等离子体反应并促进纳米级化学工程也至关重要。
