Electronic Structure of Self-Assembled Monolayers Modified with Ferrocene on a Gold Surface: Evidence of Electron Tunneling

Abstract

The electron transfer mechanism for the prototypical system ferrocenoyl-glycylcystamine (Fc-Gly-CSA) on Au(111) is investigated within the framework of density functional theory. Different Fc-Gly-CSA/Au systems, including the explicit methanol solvent and sodium perchlorate counterion, are studied. As seen from the partial density of states, electronic contributions close to the Fermi energy are found to derive only from the ferrocene units and gold atoms, while the contributions from electronic states located on the molecular spacers (Gly-CSA) are detected at lower energies, with or without the effects of the environment. These results strongly indicate a direct ferrocene-to-gold tunneling as the electron transfer mechanism across the interface.

Capacitance spectroscopy and density functional theory

“…It is important to note that CS is only experimentally resolved for the surface tethered film configuration since the redox process can store energy only here and an associated capacitance can be measured by CS. 29 We initially analysed, through eqn (14) and/or eqn (18), the variation of the total energy of the system with respect to charge Fig. 4) we can directly observe the influence of the electronic structure arising from the electrode-molecule coupling on the capacitance through the generation of new energetic states and the contribution of this process to measurable charging.…”

“…Similar observation regarding electrode-molecular energetic coupling was also confirmed recently. 29 We initially analysed, through eqn ( 14) and/or eqn (18), the variation of the total energy of the system with respect to charge Fig. 4 As discussed in the main text the positively charged gold clusteralkylthiolate-ferrocenium [AuS-(CH 2 ) 6 -Fc + ] is the chemical entity that contributes most to the redox capacitance associated with this junction.…”

Two-Dimensional Nature and the Meaning of the Density of States in Redox Monolayers

“…Electron tunneling coupling was confirmed, by others, for calculations performed in a cluster of a single molecule attached to a gold slab. Nonetheless, using a single molecule over gold slabs, there are limitations in the simulation of the properties of the redox monolayer because the 2D electronic character (Figure b) is lost in these types of simulations.…”

“…Observing the blue curve of Figure 3b, it is evidenced that the redox DOS and the states in the electrode are electronically coupled, in agreement with previous work by our group 34 which is also corroborated by the work conducted by others. 57 The electronic coupling between the redox and electron states allows us, at the Fermi level of the junction, corresponding to the halfoxidized state, to access the redox activity through the experimental measurement of C μ ̅ . The electronic coupling is controlled by a tunneling mechanism, which is not so steep (see Figure 4), permitting the electrons to overcome the electrostatic barrier imposed by the alkyl.…”

Hydrogen-Bond-Assisted, Concentration-Dependent Molecular Dimerization of Ferrocenyl Hydantoins

“…Ferrocene was exploited as an organometallic scaffold for the assembly of foldamers via intramolecular H-bonding and as a redox probe in the study of ET through peptides and other biomolecules . For example, self-assembled monolayers (SAMs) formed by Fc-terminated α-helical peptides served as suitable model systems for studying the ET through helical peptides …”