Self-assembled monolayers of ruthenocene-substituted biphenyl ethynyl thiols on gold

Ruthenocene is a promising electrochemical agent and a potential one-electron reservoir with a stable and irreversible redox system. In this respect, two new molecules, RcCCC6H4C6H4SAc (REBTA) and RcCCC6H4C6H4SH (REBTH) (Rc = (η5-C5H5)Ru(η5-C5H4); Ac = C(O)Me) were synthesized. The single crystal structure of REBTA was determined, showing that this compound forms a 3D-network structure set-up by π–π interactions of C6H4/C6H4 and C6H4/C5H5 units. Cyclic voltammetric measurements were carried out with REBTA, REBTH, and RcCCH for comparison. In view of possible electrochemical applications, REBTH and REBTH were used to prepare self-assembled monolayers (SAMs) on Au(1 1 1) substrates. The resulting SAMs were characterized by high-resolution X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy. The films were found to be well-ordered and densely packed, even though with a lower density than the analogous films formed from similar ferrocene-substituted molecules, which can be explained by the somewhat larger volume of the ruthenocene moiety, hindering the molecular packing. The presence of the acetyl protection group did not affect the quality of the resulting films significantly, even though some differences between the individual SAMs were found, dependent on the deprotection agent or its absence in the primary solution. The protection group was completely removed in all cases, even when no deprotection agent was used.