Computational investigations of electronic structure modifications of ferrocene-terminated self-assembled monolayers: effects of electron donating/withdrawing functional groups attached on the ferrocene moiety

Abstract

The electrochemical properties of chemically modified electrodes have long been a significant focus of research. Although the electronic states are directly related to the electrochemical properties, there have been only limited systematic efforts to reveal the electronic structures of adsorbed redox molecules with respect to the local environment of the redox center. In this study, density functional theory (DFT) calculations were performed for ferrocene-terminated self-assembled monolayers with different electron-donating abilities, which can be regarded as the simplest class of chemically modified electrodes. We revealed that the local electrostatic potentials, which are changed by the electron donating/withdrawing functional groups at the ferrocene moiety and the dipole field of coadsorbed inert molecules, practically determine the density of states derived from the highest occupied molecular orbital (HOMO) and its vicinities (HOMO-1 and HOMO-2) with respect to the electrode Fermi level. Therefore, to design new, sophisticated electrodes with chemical modification, one should consider not only the electronic properties of the constituent molecules, but also the local electrostatic potentials formed by these molecules and coadsorbed inert molecules.

Probing consequences of anion-dictated electrochemistry on the electrode/monolayer/electrolyte interfacial properties

“…11 ) ascribed to the highest occupied molecular orbital (HOMO) of Fc, comprised of the six 3d electrons from Fe 51 , 52 . Based on the geometry of the cyclopentadienyl (Cp) ligands, Fc has the electronic configuration (a 1 ′) 2 (e 2 ′) 4 and (a 1g ) 2 (e 2g ) 4 for the eclipsed (D 5h ) and staggered (D 5d ) conformations, respectively 53 , 54 . The XPS Fe 2p (core level) and UPS valence spectra can be tracked together because the Fc HOMO is localised to the Fe heteroatom causing them to be strongly correlated 55 , 56 .…”

Recent advances on ferrocene-based photoinitiating systems

“…Considering its low oxidation potential, ferrocene is also an excellent electron-donating group so that numerous push-pull dyes were designed with this iron (II) complex. [173][174][175][176][177][178][179][180] This metallocene which is a cheap compound is also characterized by a low toxicity so that this complex is an ideal candidate for the design of photoinitiators. [181][182][183][184][185][186][187] Compared to the aforementioned dyes, ferrocene-based photoinitiating systems exhibit advantages and disadvantages that are listed in the Table 1.…”

In situ and ex situ approaches for molecular scale understanding of electrochemical interfaces

“…Next, STM studies of the surface of the emersed electrode is presented. 57) Since the aforementioned ferrocene monolayer is difficult to be observed by STM due to slightly disordered adsorption, highly oriented pyrolytic graphite (HOPG) electrode was used here as the electrode. The electrolyte was LiPF 6 , which is commonly used as an electrolyte in Li-ion batteries, and a mixture of carbonate solvents (ethylene carbonate (EC) and dimethyl carbonate (DMC)) were used as solvents.…”

“…21) Thus, it is possible to obtain complementary information to in situ measurements, but it is currently challenging to apply this technique to cases where the affinity between the electrolyte solution and electrode is high. 57) For example, if a hydrophilic electrode is emersed from an aqueous electrolyte solution, the exposed aqueous solution remains on the electrode surface, and the electrolyte precipitates on the surface during vacuum evacuation, making it impossible to obtain any desired information. We are currently working to improve the emersion method so that it can be applied to a wide variety of sample systems.…”