Doctor of Philosophy (PhD)
Department of Chemistry
In this dissertation, the resonance coupling of chromaphoric dyes adsorbed on the surface of plasmonic nanoparticles (NPs) are investigated using a combined theoretical and experi- mental approach. Colloidal gold, gold-silver core-shell, silver-gold core-shell, and gold-silver- gold core-shell-shell NPs are considered. These NPs are thiolated with mercaptosuccinic acid, and malachite green dyes are adsorbed to the surface of the nanoparticle (NP) via elec- trostatic interactions. Second harmonic generation is used to determine the surface to the isotherm of the molecular dyes to the colloidal nanoparticle surface. Adsorption isotherms show that the SHG intensity increases as the concentration of dye increases, reaching a plateau signal at saturation. These adsorption isotherms are fit with a modified Langmuir equation to determine the best fit parameters corresponding to the free energy and adsorbate population at the surface. However, the molecular orientation and separation from the NP surface is unknown experimentally.
Strong coupling at the NP-molecule interface results in a new quantum state called a polariton. Difference extinction measurements reveal these polaritonic states overlapped in a Fano-like resonance profile. A hybrid quantum/classical theoretical model is presented to model the plasmon-molecule interactions of adsorbed molecules at the surface of a mer- captosuccinic acid capped gold and silver-gold core-shell NP. This model employs classical electrodynamics using a finite-difference time-domain (FDTD) approach for the NP response and a 3-level quantum treatment for the molecules. The coupling at the surface is highly dependent on the adsorbate/NP separation distance and molecule transition dipole angle. Increasing the separation distance or transition dipole angle results in a weaker coupling between the NP and molecule, decreasing the splitting energy. This allows us to predict the most likely separation distance and transition dipole angle for a given dye, capping agent and NP composition.
Smith, Holden Tyler, "Coupled Plasmon/Molecule Dynamics Near Core-Shell Nanoparticles: Synthesis, Ultrafast Characterization, and Quantum/Classical Modeling" (2017). LSU Doctoral Dissertations. 4151.