Probing ligand-induced modulation of metallic states in small gold nanoparticles using conduction electron spin resonance.

Thiolate-protected gold nanoparticles have a rich history as model systems for understanding the physical and chemical properties of metallic nanoscale materials that, in turn, form the basis for applications in areas such as molecular electronics, photocatalytic systems, and plasmonic solar cells. It is well known that the electronic properties of gold nanoparticles can be tuned by modifying the geometry, size and dielectric surrounding of the particle. However, much less is known of how modifications to the surface chemistry modulates the electronic properties of gold nanoparticles. In part, this stems from the fact that there are few good tools for measuring the electronic properties with the sensitivity required for following the response to subtle changes in surface chemistry. In this work, we demonstrate conduction spin electron resonance (CESR) to be a sensitive and selective probe to determine how changes in surface chemistry of gold nanoparticles affect the metallic states near the Fermi energy. Using a series of para-substituted aromatic thiolate ligands, we find that the g-factor, as measured using CESR, correlates well with experimental and computational parameters often used to understand ligand effects in classical inorganic complexes. This suggests classical inorganic reasoning can function as a framework for understanding how to control the electronic properties of gold nanoparticles using their surface chemistry.