Influence of intermolecular H-bonding on the acid-base interfacial properties of -COOH and ferrocene terminated SAM

We have explored the intermolecular interactions within a two-component self-assembled monolayer, a model system to develop our understanding of interfacial chemistry in molecular level. The redox signal of 11-ferrocenyl-1-undecanethiol (FcC11) reversibly responded to the formation of intermolecular H-bonding: The intermolecular H-bonding between the terminal carboxyl groups of MSA promoted the formation of MSA assemblies, which increased the influence of MSA on the neighboring molecules (FcC11). Meanwhile, the disordered FcC11 appeared within the locally ordered FcC11 patches, resulting in the presence of a new couple of redox peaks in the cyclic voltammograms. The surface coverage that corresponding to the H-bonding affected FcC11 increased exponentially from 0 to 3.49 × 10⁻¹⁰ mol cm⁻² as a function of the time of MSA assembly. The pK_1/2 value (the pH when half of the –COOH groups are ionized) that determined for the FcC11/MSA modified gold substrate was obviously higher than the alkanoic acids in aqueous solution. The results show that the intermolecular H-bonding between MSA molecules plays a key role in controlling the molecular assembly within the two-component self-assembled monolayer, which provides an approach for regulating the structural changes of the model membrane in molecular level.