Coupling between molecular and plasmonic resonances: Effect of molecular absorbance

In this work, we show using both experiments and classical electrodynamic simulations that plasmon splitting in resonant molecule-coated nanoparticles increases linearly as the square root of absorbance of the molecular layer. This linear relationship shows the same universal behavior established in analogous systems such as cavity-polariton and surface plasmon polariton systems. To explain this behavior, a simple physical mechanism based on linear dispersion and absorption is proposed. The insights obtained in this study can be used as a general principle for designing resonant molecule-coated nanoparticles for realizing tunable nanophotonic devices and molecular sensing.