Insights into the self-assembly of aromatic dinitroso derivatives on gold surface

Adsorption of compounds with exposed aromatic C-nitroso groups on metal surfaces provides a way for fabrication of self-assembled bilayers (SABs) owing to ability of these compounds to dimerize to azodioxides. Here, we have investigated the possibility of self-assembly and dimerization of sulfur-containing aromatic dinitroso derivatives on an Au(111) surface by using polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS), atomic force microscopy (AFM), scanning tunneling microscopy (STM), ellipsometry and water contact angle goniometry. While aromatic dinitroso derivatives are present as E-isomeric oligomers in solid state, PM-IRRAS spectra of their adlayers on gold surface revealed the presence of signals characteristic for nitroso monomers and E-azodioxy dimers. AFM and STM images of molecular adlayers showed the appearance of separate domains on an Au(111) surface suggesting formation of monolayer and bilayer-type structures. These results were further corroborated by ellipsometry measurements, which pointed to the presence of a non-uniform molecular adlayer covering gold surface. Comparison with previously studied systems of mononitroso derivatives indicates that adsorption of aromatic dinitroso derivatives on gold surface results in the formation of less ordered adlayers probably due to the steric hindrance of meta-situated nitroso groups.