The self-assembly of metal nanoparticles driven by interactions of surface-anchored ligands such as DNA, multivalent thiolates, and proteins results in 1-, 2-, and 3-dimensional nanoparticle superstructures. In the case of widely studied gold nanoparticle superstructures, the assembly is almost always mediated by thiol-anchored ligands. This results in largely static and stable structures due to the comparatively strong Au-S bond precluding dynamic events. We report generalized assembly of gold nanoclusters by the non-thiolate ligand diglyme into discrete and dynamic structures. A modified Brust-Schiffrin synthesis alters the surface of the resulting thiolate-protected gold nanoclusters by incorporating a single molecule of diglyme into the shell layer. To understand this surprising phenomenon, the assembly of Au20(SC2H4Ph)15-diglyme into Au20(SC2H4Ph)15-diglyme-Au20(SC2H4Ph)15 is explored in detail. The dimerization is validated by size exclusion chromatography, mass spectrometry, IR spectroscopy, calorimetry, and electron microscopy. Assembly is enabled through weak oxygen-gold interactions between the terminal methoxy groups in diglyme and the cluster cores. We establish a dissociation constant for dimer to monomer conversion of 20.4 µM. Theoretical models validated by transient absorption spectroscopy predict a low-spin monomer and a high-spin dimer. Close spatial coupling allows electron delocalization between the nanoparticle cores, resulting in emergent optical, electronic, and structural properties. This new generic route for dynamic assemblies of gold nanoparticles has applications in sensing, plasmonics and biology that are absent in discrete metal nanoparticles.

Dynamic assemblies of gold nanoclusters enabled by surface modifications

249th National Meeting (2015)

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