Mixed self-assembled monolayers of rigid biphenyl thiols: Impact of solvent and dipole moment

The formation of mixed self-assembled monolayers (SAMs) of different 4'- substituted-4-mercaptobiphenyl (with X = CH₃, CF₃, and SCH₃) on gold, from different solvents, has been investigated. Monolayer thickness values, estimated by ellipsometry, contact angle measurements, and external reflection absorption infrared (ERFTIR) spectroscopy confirms that > 90% of the monolayer is formed after 1 h of adsorption. The dielectric constant of the solvent, the permanent dipole moment of the substituted mercaptobiphenyl, their adsorption and desorption kinetics, and their intermolecular dipole- dipole interactions in the SAM were all found to play a crucial role in the final composition of the mixed SAMs.