Li Zhandong, Ehtesabi Sadaf, Gojare Siddhi, Richter Martin, Kupfer Stephan, Gräfe Stefanie, Kurouski Dmitry
Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843, United States.
Institute of Physical Chemistry and Abbe Center of Photonics, Friedrich Schiller University Jena, Helmholtzweg 4, 07743 Jena, Germany.
ACS Photonics. 2023 Aug 30;10(9):3390-3400. doi: 10.1021/acsphotonics.3c00893. eCollection 2023 Sep 20.
Noble metal nanostructures absorb light producing coherent oscillations of the metal's electrons, so-called localized surface plasmon resonances (LSPRs). LSPRs can decay generating hot carriers, highly energetic species that trigger chemical transformations in the molecules located on the metal surfaces. The number of chemical reactions can be expanded by coupling noble and catalytically active metals. However, it remains unclear whether such mono- and bimetallic nanostructures possess any sensitivity toward one or another chemical reaction if both of them can take place in one molecular analyte. In this study, we utilize tip-enhanced Raman spectroscopy (TERS), an emerging analytical technique that has single-molecule sensitivity and sub-nanometer spatial resolution, to investigate plasmon-driven reactivity of 2-nitro-5-thiolobenzoic acid (2-N-5TBA) on gold and gold@palladium nanoplates (AuNPs and Au@PdNPs). This molecular analyte possesses both nitro and carboxyl groups, which can be reduced or removed by hot carriers. We found that on AuNPs, 2-N-5TBA dimerized forming 4,4'-dimethylazobenzene (DMAB), the bicarbonyl derivative of DMAB, as well as 4-nitrobenzenethiol (4-NBT). Our accompanying theoretical investigation based on density functional theory (DFT) and time-dependent density functional theory (TDDFT) confirmed these findings. The theoretical analysis shows that 2-N-5TBA first dimerized forming the bicarbonyl derivative of DMAB, which then decarboxylated forming DMAB. Finally, DMAB can be further reduced leading to 4-NBT. This reaction mechanism is supported by TERS-determined yields on these three molecules on AuNPs. We also found that on Au@PdNPs, 2-N-5TBA first formed the bicarbonyl derivative of DMAB, which is then reduced to both bihydroxyl-DMAB and 4-amino-3-mercaptobenzoic acid. The yield of these reaction products on Au@PdNPs strictly follows the free-energy potential of these molecules on the metallic surfaces.
贵金属纳米结构吸收光，产生金属电子的相干振荡，即所谓的局域表面等离子体共振（LSPRs）。LSPRs可以衰减产生热载流子，即高能量物种，它们会引发位于金属表面的分子中的化学转变。通过耦合贵金属和催化活性金属，可以增加化学反应的数量。然而，如果两种化学反应都能在一种分子分析物中发生，那么这种单金属和双金属纳米结构对其中一种或另一种化学反应是否具有任何敏感性仍不清楚。在本研究中，我们利用针尖增强拉曼光谱（TERS），一种具有单分子灵敏度和亚纳米空间分辨率的新兴分析技术，来研究2-硝基-5-硫代苯甲酸（2-N-5TBA）在金和金@钯纳米片（AuNPs和Au@PdNPs）上的等离子体驱动反应性。这种分子分析物同时具有硝基和羧基，它们可以被热载流子还原或去除。我们发现，在AuNPs上，2-N-5TBA二聚形成4,4'-二甲基偶氮苯（DMAB）、DMAB的二羰基衍生物以及4-硝基苯硫酚（4-NBT）。我们基于密度泛函理论（DFT）和含时密度泛函理论（TDDFT）的伴随理论研究证实了这些发现。理论分析表明，2-N-5TBA首先二聚形成DMAB的二羰基衍生物，然后脱羧形成DMAB。最后，DMAB可以进一步还原生成4-NBT。TERS测定的这三种分子在AuNPs上的产率支持了这一反应机理。我们还发现，在Au@PdNPs上，2-N-5TBA首先形成DMAB的二羰基衍生物，然后被还原为二羟基-DMAB和4-氨基-3-巯基苯甲酸。这些反应产物在Au@PdNPs上的产率严格遵循这些分子在金属表面的自由能势。
