The impact of photon interaction frequency on plasmon-driven charge transfer to methyl viologen

Plasmonic materials, including gold and silver nanostructures, have powerful and tunable optical properties that allow them to harvest light across the visible spectrum and generate highly energetic charge carriers that can drive chemical reactions in nearby molecules. Researchers have discovered a wide variety of chemical transformations initiated by plasmon-generated charge carriers. However, we lack insights into how illumination conditions impact the charge transfer yield and efficiency in plasmon-molecule systems. In this work, we studied the effect of pulsed versus continuous wave excitation on the plasmon-driven charge transfer to methyl viologen on gold nanoparticle over mirror substrates. Pulsed and continuous wave excitation sources allowed us to understand how photon interaction frequency, or the number of photon interactions per second, influenced the steady state reduction of methyl viologen. We demonstrated that plasmon-driven charge transfer yield did not proportionally increase with increased photon interaction frequency, indicating that under pulsed illumination competing processes reduce the efficiency. Furthermore, at low photon interaction frequencies, charge transfer yield was negligible, which suggested a complex interplay between the number of photon interactions and charge transfer to methyl viologen. This work underscores the importance of illumination conditions and photon interaction frequency in plasmon-mediated charge transfer. By understanding the optimal photon interaction frequency, we can use optical engineering to achieve a similar photon flux with sunlight and efficiently drive chemical reactions.