Organization of Alkane Amines on a Gold Surface: Structure, Surface Dipole, and Electron Transfer

Surface molecular self-assembly is a fast advancing field with broad applications in molecular electronics, sensing and advanced materials. Although a large number of practical systems utilize alkanethiols, there is increasing interest in alkylamine self-assembled monolayers (SAMs). In this article, the molecular and electronic structure of alkylamine SAMs on Au surfaces was studied. It was found that amine-terminated alkanes self-assemble, forming a compact layer with the amine headgroup interacting directly with the Au surface and the hydrocarbon backbone tilted by around 30° with respect to the surface normal. The dense layers formed substantially decrease electron tunneling across the metal/solution interface and form a dipole layer with positive charges residing at the monolayer/vacuum interface

Molecular and Electronic Structure of Self-Assembled Monolayers Containing Ruthenium(II) Complexes on Gold Surfaces

Ru­(II) bipyridyl complexes were covalently bonded to self-assembled monolayers (SAM) on Au surfaces. Their molecular and electronic structure was studied by means of polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), photoelectron spectroscopies, scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. We found that attaching the Ru complex to the SAM does not cause great modifications to its molecular structure, which retains the alkyl chain 30 deg tilted with respect to the surface normal. Furthermore, the Ru center is located 20 Å away from the metal surface, i.e., at a sufficient distance to prevent direct electronic interaction with the substrate. Indeed the electronic structure of the Ru complex is similar to that of the free molecule with a HOMO molecular orbital mainly based on the Ru center located 2.1 eV below the Fermi edge and the LUMO molecular orbital based on the bipyridine groups located 1 eV above the Fermi level

Self-Assembled Monolayers of NH₂‑Terminated Thiolates: Order, p<i>K</i>_a, and Specific Adsorption

Self-assembled monolayers (SAMs) of amino-terminated alkanethiols on Au were characterized by a combination of electrochemical (LSV, CV, and EIS) and spectroscopic (XPS and SER) techniques. Clear correlations were obtained between the apparent surface p<i>K</i>_a values determined by impedimetric titrations and order parameters such as the content of trans conformers in the SAMs. These results contrast with previous studies that exhibit dispersions of up to 6 pH units in the reported p<i>K</i>_a values. In addition, we determined that inorganic and organic phosphate species bind specifically to these SAMs mediating adsorption and heterogeneous electron transfer of positively charged macromolecules such as cytochrome <i>c</i>