Electron hopping and electronic conductivity in monolayers of alkanethiol-stabilized gold nano-clusters at the air/water interface

Morphology of Langmuir monolayers of gold clusters stabilized with a series of alkanethiols was investigated at the air/water interface with Brewster Angle Microscopy which revealed substantial differences depending on the length of the alkyl chains (clusters stabilized with C₈ and C₁₆ thiols were investigated). 2D electrochemical measurements carried out with line micro-band electrodes showed negligible electronic conductivity of all monolayers even in their most compressed state, apparently due to the presence of the stabilizing alkyl chains on the surface of the clusters. The same electrochemical measurement showed, however, full redox conductivity in the monolayers of gold nano-cluster stabilized with alkanethiols, 20% of which were terminated with ferrocene. In those cases, redox conductivity is supported by a facile electron hopping (self-exchange rate constant was measured to be ≥ 4.4 × 10⁶ M^-1 s^-1) between neighboring ferrocene/ferrocenium sites.