Active Tuning of Strong Coupling States between Dye Excitons and Localized Surface Plasmons via Electrochemical Potential Control

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Here we report the tuning of a number of excited dye molecules that were strongly coupled with the localized surface plasmons (LSPs) of Au nanostructures by electrochemical potential control. Using the redox-state-tuned dye molecules and several types of metal nanostructures with distinct LSP energies, active control of the high coupling strength was achieved via an electrochemical potential-based control method. One interesting finding of the present work is that the parabolic behavior of the coupling strength in the range between 0.10 and 0.27 eV is dependent on the electrochemical potential; this has not been observed previously. Anticrossing plots showing the energies of the upper and lower states of the coupling to the LSP energy suggest that the number of dye molecules contained in the cavity-confined LSP field is controlled not only by the redox states of the dye molecules but also by the interactions between the dyes and the metal surfaces. The present finding provides a novel route to control lig...