Electron Transfer through 3D Mono layers on Au-25 Clusters

S Antonello and G Arrigoni and T Dainese and M De Nardi and G Parisio and L Perotti and A Rene and A Venzo and F Maran, ACS NANO, 8, 2788-2795 (2014).

DOI: 10.1021/nn406504k

The monolayer protecting small gold nanoparticles (monolayer-protected clusters, MPCs) is generally represented as the 3D equivalent of 20 self-assembled monolayers (SAMs) on extended gold surfaces. However, despite the growing relevance of MPCs in important applied areas, such as catalysis and nanomedicine, our knowledge of the structure of 3D SAMs in solution is still extremely limited. We prepared a large series of monodisperse Au-25(SCnH2n+1)(18) clusters (n = 2, 4, 6, 8, 10, 12, 14, 16, 18) and studied how electrons tunnel through these monolayers. Electron transfer results, nicely supported by H-1 NMR spectroscopy, IR absorption spectroscopy, and molecular dynamics results, show that there is a critical ligand length marking the transition between short ligands, which form a quite fluid monolayer structure, and longer alkyl chains, which self-organize into bundles. At variance with the truly protecting 20 SAMs, efficient electronic communication of the Au-25 core with the outer environment is thus possible even for long alkyl chains. These conclusions provide a, different picture of how an ultrasmall gold core talks with the environment through/with its protecting but not-so- shielding monolayer.

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