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

Abstract

It has been suggested that the transport of charge in molecular electronics and redox junctions is, at the sub-nanoscale, that is, for dimensions lower than 5 nm, fundamentally related [Phys. Chem. Chem. Phys, 2020, 10.1039/D0CP01621G]. In the present work, supported on conceptual and computational methods of density functional theory, we provided additional evidence for this relationship, by showing that redox molecular structures assembled over conductive electrodes resemble, in terms of their electrochemical DOS, 2DEG structures. Owing to the fact that 2DEG structures are commonly taken as the fundamental physical model applied in the designing of field-effect transistors, an electrochemical “version” is important as a blueprint for the development of devices required in electrochemical environments. Additionally, the effect of the dielectrics of the solvent and of the counter ions over the electrochemical 2D DOS of redox molecular films was studied using hybrid computational methods. The results of computational simulation of the DOS were qualitatively compared with those obtained experimentally.

Quantum rate as a spectroscopic methodology for measuring the electronic structure of quantum dots

“…This QRS methodology allows us to define the rate at which the states of the QDs communicate with the electrode owing to an electric-field perturbation of the QD states through the electrode. Theoretically, this quantum rate can be equivalently defined as the ratio between the quantum of conductance G and the electrochemical capacitance C μ as, given by 10,11,14 where , with g s as the spin degeneracy of the electron (thus taking a value of 2) and e as the elementary charge of the electron. The term of G represents the electron transmission probability through n individual quantum channels communicating with the QDs by an energy perturbation imposed by the electrode owing to the modulation of the electric field, stating for a function that models the nature and strength of the electron coupling of the QD states with the electrode.…”

“…This QRS methodology allows us to define the rate at which the states of the QDs communicate with the electrode owing to an electric-field perturbation of the QD states through the electrode. Theoretically, this quantum rate can be equivalently defined as the ratio between the quantum of conductance G and the electrochemical capacitance C m as, given by 10,11,14…”

“…8 QRS is an electric spectroscopy method that is fundamentally based on the quantum rate theoretical principles. 9–11 For instance, besides the application of the principles to characterize single-layer graphene, 8,12 it has also been possible to access the DOS of mixed metal-oxide films 13 and organic assemblies, 14 such as molecular redox-active films. 11 Furthermore, quantum rate theory has been useful for the study of quantum electrochemical principles, 11,15 for example demonstrating that charge transfer resistance is essentially a specific setting of the quantum conductance principle.…”

Beyond the Laviron Method: A New Mathematical Treatment for Analyzing the Faradaic Current in Reversible, Quasi-Reversible, and Irreversible Cyclic Voltammetry of Adsorbed Redox Species

“…Understanding the voltammetric responses of adsorbed redox species on metal electrodes is relevant to several technical areas including molecular electronics, electrocatalysis, and chemical sensors. − Accordingly, an extensive literature exists for deciphering cyclic voltammetric data as a function of physical parameters of interest. − Curiously, although methods to fit and analyze the reversible and irreversible voltammetric responses of adsorbed redox species were developed early on, , strategies to understand quasi-reversible voltammetric responses remain scarce with one notable exception. This curious gap in the literature reflects the severe complexity in the mathematic relations between the surface concentrations of redox species and the operative rate expression (vide infra).…”

Ab Initio QM/MM Simulation of Ferrocene Homogeneous Electron-Transfer Reaction

“…Furthermore, in a typical electroactive molecular layer, − there are specific intermolecular interactions that originate from the mesoscopic two-dimensional character of these structures . The confinement of electroactive molecules (such as redox switches) to few nanometers (i.e., from 0.8 to 2 nm) of the surface of an electrode modifies the electron-transfer process occurring between the molecules and the electrode states ,,− and, in such conditions, additionally, the charge transfer occurs in a heterogeneous situation.…”