Roles of Near and Far Fields in Plasmon-Enhanced Singlet Oxygen Production

In plasmon-enhanced singlet oxygen (¹O₂) production, irradiation of a hybrid photosensitizer-metal nanoparticle leads to a significant alteration of the photosensitizer's ¹O₂ yield. The quest for a more rational design of these nanomaterials calls for a better understanding of the enhancement mechanism that, to this day, remains largely unexplored. Herein, we introduce a new methodology to distinguish the near- and far-field contributions to the plasmon-enhanced ¹O₂ production using a tunable model nanoplatform, Rose Bengal-decorated silica-coated metal nanoparticles. By correlating ¹O₂ production to the experimental and simulated optical properties of our nanoparticles, we effectively discriminate how the near- and far-field effects contribute to the plasmonic interactions. We show that these effects work in synergy; i.e., for nanoparticles with a similar local field, the production of ¹O₂ correlates with maximized scattering yields. Our results expound the critical plasmonic aspects in terms of near and far fields for the design of an efficient hybrid plasmonic nanoparticle photosensitizer.