Charge Transfer on the Nanoscale: Current Status

Chemical Society Reviews, 2020

This tutorial review considers how the fundamental quantized properties associated with charge transport and storage, particularly in molecular films, are linked in a manner that spans nanoscale electronics, electrochemistry, redox switching, and derived nanoscale sensing.

Chemical Reviews, 2008

Annals of the New York Academy of Sciences, 2006

Capacitance and other properties of nanoelectrodes, finite-size metal clusters envisaged for use in complex molecular-electronic devices, are discussed. The applicability of classical electrostatics (Coulomb's and Gauss' law, Poisson's equation, etc.) to atomistic systems is investigated and the self-energy necessary to store a finite charge on an atom is found to be of central importance. In particular, the neglect of electron exchange is found to introduce severe limitations, with quantum calculations predicting fundamentally different electronic structures. Also, the well-known poor representation of the atomic self-energy inherent to modern DFT is discussed, along with its implications for molecular electronics calculations. An INDO/S method is introduced with new parameters for gold. This is the simplest approximate computational scheme that correctly includes quantum electrostatic, resonance, and spin effects, and is capable of describing arbitrary excited electronic states. Encouraging results are obtained for some trial problems. In particular, voltage differential between the electrodes in electrode-molecule-electrode conduction is obtained, not through an a priori prescription but rather by moving whole electrons between the electrodes and analyzing the response. The voltage drops across the molecule-electrode junctions and the central molecular region are then deduced. This alternative to the current Landauer-based 1-particle transmission equations for electrode-molecule-electrode conduction is discussed in terms of the use of the electronic states of the system. It provides a proper description not only of conduction via electrode-to-molecule charge or hole transfer but also of conduction via simultaneous charge and hole transfer via low-lying excited molecular electronic states, including the ability to account for electroluminescence and other chemical effects. In addition, various aspects of our research on the quantitative prediction of the I(V) curves for electrodemolecule-electrode conduction are reviewed, including demonstration of the equivalence of the formalisms generated by the Datta and the Mujica-Ratner groups, and the development of analytically solvable paradigms, including the conduction through a linear-chain Hückel wire.

Russian Journal of Electrochemistry

Quantum-chemical approaches that have been used lately for computing Franck–Condon barriers for electron transfer reactions are analyzed. Attention is focused on the processes whose description goes beyond the linear response approximation, including redox reactions with the cleavage of chemical bonds. Various approaches that take into account the solvation effects are discussed. The role played by the cluster models of the electrode in the description of specific interaction of reactants and products with the electrode surface is emphasized. The influence the dynamics of the nearest coordination sphere of metal aquacomplexes has on the electron transfer rate are interpreted anew. Examples of calculation of the electron penetration probability are considered, and important qualitative effects associated with the dependence of this parameter on the reactant orientation and the electrode charge are analyzed. Urgent problems the quantum electrochemistry faces in the near future are rev...

The Journal of Physical Chemistry B, 2006

The dynamics of heterogeneous electron transfer (ET) from the polycyclic aromatic chromophore perylene to nanostructured TiO 2 anatase was investigated for two different anchor groups with transient absorption spectroscopy in an ultrahigh vacuum. Data from ultraviolet photoelectron spectroscopy and from linear absorption spectroscopy showed that the donor state of the chromophore was located around 900 meV above the lower edge of the conduction band. With the wide band limit fulfilled the rate of the heterogeneous ET reaction was only controlled by the strength of the electronic coupling and not reduced by Franck-Condon factors. Two different time constants for the electron transfer, i.e., 13 and 28 fs, were measured with carboxylic acid and phosphonic acid as the respective anchor groups. The difference in the ET time constants was explained with the different extension of the donor orbital onto the respective anchor group to reach the empty electronic states of the semiconductor. The time constants were extracted by means of a simple rate equation model. The validity of applying this model on this ultrafast time scale was verified by comparing the rate equation model with an optical Bloch equation model.

Current Opinion in Electrochemistry, 2019

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Journal of the Brazilian Chemical Society, 2013

Nos últimos anos, montagens do tipo eletrodo-camada orgânica-nanopartícula têm atraído interesse de pesquisa considerável para sistemas onde o eletrodo é passivado na ausência das nanopartículas. Isso acontece porque tem-se observado que se a camada orgânica for uma boa monocamada auto-montada para passivar o eletrodo, a presença de nanopartículas "ligam" a eletroquímica faradaica, e porque a transferência de elétrons entre o eletrodo e as nanopartículas é aparentemente independente da espessura da camada orgânica. Este review 1) destaca quão importante são as observações experimentais a respeito deste fenômeno, 2) discute uma descrição teórica recente para explicar as observações que acabaram de ser apoiadas por evidências experimentais e 3) fornece um resumo sobre a aplicação desses sistemas em sensores e sistemas fotovoltaicos. In the last few years electrode-organic layer-nanoparticle constructs have attracted considerable research interest for systems where in the absence of the nanoparticles the electrode is passivated. This is because it has been observed that if the organic layer is a good self-assembled monolayer that passivates the electrode, the presence of the nanoparticles "switches on" faradaic electrochemistry and because electron transfer between the electrode and the nanoparticles is apparently independent of the thickness of the organic layer. This review 1) outlines the full extent of the experimental observations regarding this phenomenon, 2) discusses a recent theoretical description to explain the observations that have just been supported with experimental evidences and 3) provides an overview of the application of these systems in sensing and photovoltaics.

Chemical Physics, 2006

Optically induced charge transfer between adsorbed molecules and a metal electrode was predicted by Hush to lead to new electronic absorption features, but has been only rarely observed experimentally. Interfacial charge transfer absorption (IFCTA) provides information concerning the barriers to charge transfer between molecules and the metal/semiconductor and the magnitude of the electronic coupling and could thus provide a powerful tool for understanding interfacial charge-transfer kinetics. Here, we utilize a previously published model [C. Creutz, B.S. Brunschwig, N. Sutin, J. Phys. Chem. B 109 10251] to predict IFCTA spectra of metal-molecule assemblies and compare the literature observations to these predictions. We conclude that, in general, the electronic coupling between molecular adsorbates and the metal levels is so small that IFCTA is not detectable. However, few experiments designed to detect IFCTA have been done. We suggest approaches to optimizing the conditions for observing the process.

2018

Over the years many techniques have been proposed for the purpose of the formation of electrically conducting metal-molecule-metal junctions. One such technique utilizes gold-nanoparticles (AuNPs) ...

Faraday Discussions, 2006

We address some physical features associated with long-range interfacial electron transfer (ET) of metalloproteins in both electrochemical and electrochemical scanning tunneling microscopy (ECSTM) configurations, which offer a brief foundation for understanding of the ET mechanisms. These features are illustrated experimentally by new developments of two systems with the blue copper protein azurin and enzyme nitrite reductase as model metalloproteins. Azurin and nitrite reductase were assembled on Au(111) surfaces by molecular wiring to establish effective electronic coupling between the redox centers in the proteins and the electrode surface for ET and biological electrocatalysis. With such assemblies, interfacial ET proceeds through chemically defined and well oriented sites and parallels biological ET. In the case of azurin, the ET properties can be characterized comprehensively and even down to the single-molecule level with direct observation of redox-gated electron tunnelling resonance. Molecular wiring using a p-conjugated thiol is suitable for assembling monolayers of the enzyme with catalytic activity well-retained. The catalytic mechanism involves multiple-ET steps including both intramolecular and interfacial processes. Interestingly, ET appears to exhibit a substrate-gated pattern observed preliminarily in both voltammetry and ECSTM.