Redox-Controlled Ion-Pairing Association of Anionic Surfactant to Ferrocene-Terminated Self-Assembled Monolayers.

The redox-induced pairing from aqueous solution of a homologous series of sodium n-alkyl sulfate (NaCnSO4) surfactants of 6, 8, 10, and 12 carbons with gold-tethered self-assembled monolayers (SAMs) of ferrocenyldodecanethiolate (FcC12SAu) is investigated by cyclic voltammetry combined with surface plasmon resonance (SPR) spectroscopy. The adsorbed layer thicknesses and surface coverages are consistent with the formation of a monolayer of CnSO4(-) at the oxidized FcC12SAu SAM/aqueous solution interface. A comparison of the anodic charge density with the SPR data indicates that approximately 60% of the adsorbed surfactant anions are paired with SAM-bound ferroceniums, suggesting an interdigitated layer structure.