Collaborative Research: Electronic and Geometric Structure of n-Glyme Assembled Metal Clusters

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Metal nanoparticles can be just a few nanometers in size and contain just tens to hundreds of metal atoms. When the nanoparticles are isolated from one another, exposure to light typically results in heating of the particle, which then dissipates energy into the surrounding solvent. However, connect two particles together and that light absorption can be converted into a bright luminescence. With support from the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry, Professors Christopher Ackerson (Colorado State University), Christine Aikens (Kansas State University), and Kenneth Knappenberger (Pennsylvania State University) are working to understand the mechanism of this light emission. The team combines precision nanoparticle synthesis and characterization with cutting-edge theoretical calculations and experimental spectroscopy to determine the unique luminescence properties of these systems. Their discoveries could improve bioimaging and impact emerging quantum information technologies. The project also provides a unique multi-disciplinary environment for student training, and outreach activities to K-12 students are introducing underrepresented students to scientific research. The primary thrusts of this proposal are to determine how ligand substitution affects the geometric and electronic structure of quantum-confined gold nanoclusters (AuNCs) and their assemblies, and to understand the influence of these properties on electronic relaxation dynamics and photoluminescence yields. The team is also developing an understanding of how the properties of AuNC monomers impact electronically coupled dimers and extended structures. The proposed research features structurally precise monolayer-protected gold clusters and progresses to include n-glyme-bridged multimers. The specific objectives include: 1) to determine the compatible ligands for which glyme molecules can be incorporated into the AuNC passivation shell, and to understand the range of clusters that can be assembled using glyme-driven chemistry; 2) to describe the nature of the interaction -- both electronically and geometrically -- of glyme with AuNC monomers and larger assemblies; and 3) to describe how the properties described in 1 and 2 affect state-resolved carrier dynamics of AuNC monomers, inter-cluster electronic coupling and transfer, and photoluminescence emission. These goals are being achieved by combining colloidal AuNC synthesis and purification, computational-based predictions, and experimental electron dynamics research. The proposed efforts include plans to provide student education at the graduate and undergraduate levels in three pillars of nanoscience.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.