Hot-Hole-Induced Molecular Scissoring: A Case Study of Plasmon-Driven Decarboxylation of Aromatic Carboxylates,The Journal of Physical Chemistry C

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Hot-Hole-Induced Molecular Scissoring: A Case Study of Plasmon-Driven Decarboxylation of Aromatic Carboxylates
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2021-09-16 , DOI: 10.1021/acs.jpcc.1c07177
Qingfeng Zhang ₁ , Kexun Chen ₁ , Hui Wang ₁

Affiliation

Optically excited plasmonic nanostructures may function as molecular scissors with unique capabilities to cleave specific chemical bonds in molecular adsorbates through either plasmon-enhanced intramolecular electronic excitations or injection of photoexcited hot electrons into adsorbate orbitals. Here we chose plasmon-driven decarboxylation of aromatic carboxylates as a model reaction system to demonstrate that plasmonic hot holes, instead of electrons, could also be effectively harnessed to trigger regioselective bond cleavage in molecular adsorbates. We used surface-enhanced Raman scattering as an in situ spectroscopic tool to precisely monitor the decarboxylation reactions in real time and further correlate the reaction kinetics to local-field enhancements. The apparent rate constants were proportional to the fourth power of the local-field enhancements and exhibited a superlinear dependence on the excitation powers. Such a non-linear power dependence of reaction rates was a hallmark of hot-carrier-driven reactions involving multiphoton absorption rather than photothermally triggered processes, as inferred by the results of Raman thermometry. The decarboxylation reactions took place only at the surface sites with local-field intensities exceeding a certain threshold value, whereas the molecules experiencing weaker local fields below the threshold remained essentially unreactive. With the aid of density functional theory calculations, we were able to further relate the experimentally observed pH dependence of reaction kinetics to the frontier orbital energies of the hole-accepting adsorbates and the redox potentials of the electron-accepting protons, both of which could be modulated by adjusting the pH of the reaction medium.

中文翻译：

热孔诱导的分子剪断：等离子驱动芳族羧酸酯脱羧的案例研究

光激发等离子体纳米结构可以作为分子剪刀，具有独特的能力，通过等离子体增强的分子内电子激发或将光激发热电子注入吸附质轨道，切割分子吸附质中的特定化学键。在这里，我们选择等离子体驱动的芳族羧酸酯脱羧作为模型反应系统，以证明等离子体热空穴而不是电子也可以有效地用于触发分子吸附物中的区域选择性键裂解。我们使用表面增强拉曼散射作为原位光谱工具，可实时精确监测脱羧反应，并进一步将反应动力学与局部场增强相关联。表观速率常数与局部场增强的四次方成正比，并表现出对激发功率的超线性依赖性。反应速率的这种非线性功率依赖性是热载流子驱动反应的标志，涉及多光子吸收而不是光热触发过程，如拉曼温度测量的结果所推断的那样。脱羧反应仅发生在局部场强度超过某个阈值的表面位点，而经历低于阈值的较弱局部场的分子基本上保持不反应。借助密度泛函理论计算，

更新日期：2021-09-30

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