Micromechanical Redox Actuation by Self-Assembled Monolayers of Ferrocenylalkanethiolates: Evens Push More Than Odds.

Microcantilever transducers can be valuable tools for the investigation of physicochemical processes in organized molecular films. Gold-coated cantilevers are used here to investigate the electrochemomechanics of redox-active self-assembled monolayers (SAMs) of ferrocenylalkanethiolates (Fc(CH2) nS) of different alkyl chain lengths. A significant odd-even effect is observed in the surface stress and cantilever movement generated by the oxidation of the SAM-confined ferrocenes as the number of methylene units n in the SAM backbone is varied. We demonstrate that stronger alkyl chain-chain interactions are at the origin of the larger surface stresses generated by SAMs with an even versus odd n. The findings highlight the impact of subtle structural effects and weak van der Waals interactions on the mechanical actuation produced by redox reactions in self-assembled systems.