When metals get all excited!

Light doesn’t just reveal chemistry — it can power it. Plasmonic metals like gold and silver use light to generate energetic “hot” charge carriers and intense local fields, enabling reactions that don’t occur under normal conditions. These effects have made plasmon-driven chemistry a promising route for creating new materials and nanoscale structures. The Optical Nanospectroscopy Group (Janina Kneipp) examined how allyl mercaptan reacts on silver and gold nanoparticles and how localized surface plasmon resonances influence that chemistry. Using enhanced Raman techniques and full-spectrum analysis, they track the reaction as it forms alkyl oligomers with oxidized sulfur groups. Reaction rates shift with excitation wavelength and intensity, and direct evidence of carbon–metal bond formation points to hot-electron activation of the molecule’s double bond. their  results show that aligning plasmon resonances with interband transitions greatly boosts reaction efficiency, revealing how plasmonic surfaces can drive bond activation and enable the tailored fabrication of functional nanomaterials. Find out more in their ACS Catalysis Article!

Abstract

The generation of hot charge carriers from plasmonic metals has been harnessed in a range of plasmon-catalyzed reactions. Here, we report the chemical reaction of allyl mercaptan (2-propene-1-thiol) on different plasmonic silver and gold substrates and elucidate the role of localized surface plasmon resonances in the reaction. The decay of localized plasmons can create hot carriers. Additionally, high local fields of the plasmonic nanoparticles at a matching energy range enhance directly optically excited interband transitions in metal nanoparticles. Moreover, the high local fields enable observation of surface-enhanced Raman scattering (SERS) and also nonlinear surface-enhanced hyper-Raman scattering (SEHRS) from the reaction product. We introduce monitoring of the reaction-related change based on the full spectral profile represented by the principal component scores rather than by individual spectral signals, and thereby can base the kinetic description on different reactant and product functional groups at the same time. As evidenced by the plasmon-enhanced vibrational spectra collected in the course of the reaction, allyl mercaptan forms alkyl oligomers with different chain lengths with oxidized sulfur groups. The direct observation of carbon–metal bond formation on silver and gold nanostructures and the dependence of the reaction rates on the excitation wavelength and intensity indicate an activation of the reaction by hot electrons. We propose that their interaction with the double bond initiates a radical oligomerization that is accompanied by a plasmon-supported elimination of hydrogen to enable the formation of unsaturated chains. A high reaction efficiency is observed when plasmon resonances fall in the energy range of interband transitions, as it occurs in some experiments conducted with gold nanoparticles, and when high local fields can enhance the production of hot carriers. The activation of double bonds on plasmonic surfaces can be used to produce functionalized nanostructures and materials.