Mol. dye interactions with colloidal gold and gold- silver- gold core- shell- shell nanoparticles are studied using second
harmonic generation (SHG) , extinction spectroscopy, and transient absorption spectroscopy. The adsorption isotherms of
several dyes such as malachite green, brilliant green, and rhodamine 110 to the colloidal nanoparticle surface in water are
measured with SHG and the results are fit using the modified Langmuir model to det. the free energies of adsorption and the
adsorbate site densities. Complementary measurements of the extinction spectra of the combined dye and nanoparticle solns.
with subtractions from the spectra of the dye and nanoparticles alone at corresponding concns. reveal strong polaritonic
states from resonant coupling that depend on the dye- plasmonic nanoparticle interactions. The resonant coupling
spectroscopy agrees with computational simulations using a multiscale hybrid /classical approach, showing polariton peaks
that overlap with a Fano- type profile. The plasmonic spectra of core- shell- shell nanoparticles are controlled by changing the
shell thicknesses for improved spectral overlap with the adsorbed dyes, resulting in significantly enhanced resonant coupling
peaks. Addnl., transient absorption spectroscopy on excited- state dynamics of the dye- nanoparticle solns. show the
convolution of plasmonic and mol. dynamics to study effects from energy transfer, mol. hindrance, and optical field
enhancements. The results are compared to fluorescent quenching and enhancement measurements to understand the overall,
time- dependent optical and energetic interactions between dye mols. and colloidal plasmonic nanoparticle surfaces.
These linear, nonlinear, and ultrafast spectroscopic investigations provide important information that can be utilized for
improved plasmon- enhanced mol. sensing applications in aq. soln