IR spectroscopic characterization of SAMs made from a homologous series of pyridine disulfides

A homologous series of pyridine-terminated organic disulfides has been used to prepare self-assembled monolayers (SAMs) of the corresponding thiolates on Au substrates. A characterization using IR-spectroscopy reveals surprisingly large differences between the members of the homologous series. We find a strong evidence for partial protonation of the pyridine-terminated organic surfaces exposed by the corresponding SAMs in particular in the case where the SH-group is directly attached to the pyridine ring. The assignment of the vibrational frequencies is based on ab initio calculations for the investigated thiol monomers.