Collaborative Research: Excited State Dynamics of Structurally Precise Metal Nanoclusters

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These awards by the Macromolecular/Supramolecular/Nanochemistry Program in the Division of Chemistry to Christine Aikens (Kansas State University), Ken Knappenberger (Florida State University), and Chris Ackerson (Colorado State University) develop the ability to predict how metal particles with dimensions on the order of one-billionth of a meter (i.e., nanoparticles) interact with light. Such metal nanoparticles may, in the long term, become functional components in solar-to-electric energy conversion devices, optical sensors, and medical diagnostics and therapeutics, among others. Currently, the lack of understanding how light provokes energy flow through these materials limits their applications. The collaborative team combines cutting-edge theoretical and experimental spectroscopy along with precision nanoparticle synthesis and characterization. They facilitate their multi-disciplinary research project by developing graduate student training courses focused on modeling, measurement, and preparation of structurally precise photonic nanoparticles. The team is also strongly engaged in outreach to K-12 students and educators; is actively involved in incorporating research into the undergraduate curricula at each of their respective universitie;, and is committed to the involvement of underrepresented students in scientific research and education.The primary thrusts of this effort are to determine how electronic energy relaxation affects the nanophotonic properties of structurally precise metal nanoparticles in the 1-2 nm size domain. The research features an emergent class of nanophotonic materials: monolayer-protected clusters (MPCs), which can be synthesized and isolated with atomic precision. These materials represent an intermediate class of materials between bulk metallic materials and smaller photo-excited molecules. The program of study provides nanoparticle-specific descriptions for fundamental processes involved such as electron-phonon coupling, which are critical for determining the functional properties of nanophotonic materials. The research investigates the interplay between MPC structural parameters and electronic relaxation. The specific objectives are: 1) to determine the mechanisms of electron-phonon and electron-vibrational coupling and their influence on the electronic relaxation dynamics of Au25(SR)18 MPCs, where SR is an alkanethiol; 2) to understand the effects of metal doping on MPC dynamics; 3) to describe how electron-phonon coupling changes with increasing MPC dimensions; and 4) to investigate the influence of MPC ligand band structure on electron dynamics.