Electron Transfer Coupling Matrix Element Research Articles

The potential impact of the graphene oxide on the cytochrome c − from the insight of electron transfer theory

We have studied the electron transfer (ET) reaction between the cytochrome c (Cyt c) and the graphene oxide (GO). The ET reorganization energy, the ET coupling matrix element and the ET rate constant for Cyt c-GO system have been calculated using QM+MM method based on semi-classical Marcus theory. The total reorganization energy of Cyt c and GO system is about 0.9 eV. Although the conformation of Cyt c and the relative orientation of Cyt c to GO have little influence on the reorganization energy, they make a significant influence on the coupling matrix element, which results in the tremendously different ET rate constants by different orders of magnitudes. Comparing the ET rate constant of Cyt c-Go system with that between Cyt c and Cyt c1, it indicates that there is a competition between GO and Cyt c1 in the ET reaction with Cyt c.

FMO3-LCMO study of electron transfer coupling matrix element and pathway: Application to hole transfer between two tryptophans through cis- and trans-polyproline-linker systems

The linear-combination of fragment molecular orbitals with three-body correction (FMO3-LCMO) is examined for electron transfer (ET) coupling matrix elements and ET pathway analysis, with application to hole transfer between two tryptophans bridged by cis- and trans-polyproline linker conformations. A projection to the minimal-valence-plus-core FMO space was found to give sufficient accuracy with significant reduction of computational cost while avoiding the problem of linear dependence of FMOs stemming from involvement of bond detached atoms.

ELECTRON TRANSFER THROUGH NON-HYDROGEN AND HYDROGEN BONDED INTERMOLECULAR TUNNEL JUNCTIONS: A COMPUTATIONAL STUDY

The nature of electron transfer through intermolecular tunnel junctions has been studied. Intermolecular junctions feature non-hydrogen and hydrogen bonded interactions and are defined by the end groups of pairs of functionalized conjugated alkenes. We compared the distant dependent electron transfer from donor to acceptor group attached to the other sides of those functionalized conjugated alkenes. Study shows electron transfer coupling matrix element for these intermolecular junctions decays exponentially as a function of junction separation and quite substantial in energetically favourable hydrogen bonded intermolecular junctions.

Calculation of the electron transfer coupling matrix element in diabatic reactions

AbstractElectron transfer coupling matrix elements, T values, are evaluated for three typical electron transfer (ET) systems: phenoxyl radical–phenol, DNA fragments, and copper‐containing nitrite reductase. Fragment charge difference method is improved by introducing the Pipek‐Mezey localization method. We found that T values are stably evaluated by using beta lowest unoccupied molecular orbitals, which are significantly more easily found compared to alpha ET orbitals. This technique is essential for metal‐containing ET systems. Redox‐active orbitals for the donor and accepter sites are derived by localizing the ET orbitals, and other related parameters such as the state energy gap and the localization index are also obtained. These orbitals and parameters are very useful to characterize their ET reactions. These practical techniques can be utilized for other general ET reactions. © 2012 Wiley Periodicals, Inc.

Length-dependence of electron transfer coupling matrix in polyene wires: Ab initio molecular orbital theory study

The electron transfer (ET) properties of π-electron conjugated quasi-one-dimensional molecular wires, consisting of polyene, [>CC<]n (n = 1–11), including β-carotene, is investigated using ab initio molecular orbital theory within Koopmans theorem (KT) approach. The ET coupling matrix element, VDA, for 1,3-trans-butadiene molecule calculated with the KT approach shows excellent agreement with the corresponding results obtained with two-state model. The calculated values of VDA for the polyene oligomers exhibit exponential decrease in magnitude with increasing length of the wire. However, the decay curve exhibits three different regimes. The magnitude of the decay constant, β, decreases with the increase in length of the wire. A highly delocalized π-electron cloud in the polyene chain appears to facilitate retention of the electronic coupling at large separations between the donor and acceptor centers. Published 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009

Ab initio investigation on electron transfer in molecular electronic devices: A minimal model study

The electron transfer of a model system, Au-benzene-1,4-dithiolate-Au, in the presence of an external electric field is investigated. Both the cis- and trans-conformations are considered. The calculations show that, for both conformations, the interatomic distance between gold and sulfur on the site with an extra localized electron is shortened by about 0.17 Å when the extra electron transfers to the other site. On the other hand, the reorganization energies of both conformations are almost the same, about 29 kJ mol −1. The electron transfer coupling matrix elements are 0.42 and 0.73 kJ mol −1, while the threshold field strengths are 8.5 × 10 −4 and 7.4 × 10 −4 a.u. for the cis- and trans-conformations, respectively.

Synthesis, Crystal Structure, and Prediction of Hole Mobilities of 2,7‘-Ethylenebis(8-hydroxyquinoline)

A novel bis(8-hydroxyquinoline) compound based on formylquinolinol has been synthesized and characterized by X-ray single-crystal diffraction, IR, UV, 1H NMR, MS, and elemental analysis. It is reported that the formylation of 8-hydroxyquinoline gives substitution at the 7-position by X-ray structure analysis. In comparison with the spectrum for 8-hydroxyquinoline, the fluorescence spectrum of this novel bis(8-hydroxyquinoline) species shows a red shift. The optimized geometrical structures of the neutral and cationic states on 2,7‘-ethylenebis(8-hydroxyquinoline) were optimized at the DFT B3LYP/cc-pvdz level. The results are in good agreement with the reference and experimental values. The hole mobility of 2,7‘-ethylenebis(8-hydroxyquinoline) has been predicted by the reorganization energy and electron-transfer coupling matrix elements using quantum mechanics (QM), and the value is 1.612 cm2/(V s).

Ab initio quantum chemical study of electron transfer in carboranes

The electron transfer (ET) properties of 10- and 12-vertex carboranes are investigated by the ab initio Hartree–Fock method within the Marcus-Hush (MH) two-state model and the Koopman theorem (KT) approach. The calculated value of the ET coupling matrix element, V AB, is consistently higher in the KT approach than in the MH two-state model. For the carborane molecules functionalized by –CH 2 groups at C-vertices, V AB strongly depends on the relative orientation of the planes containing the terminal –CH 2 groups. The predicted conformation dependence of V AB offers a molecular mechanism to control ET between two active centers in molecular systems.

Predictions of Hole Mobilities in Oligoacene Organic Semiconductors from Quantum Mechanical Calculations

We estimate the hole mobility for oligoacene crystals using quantum mechanics (QM) to calculate the reorganization energy and electron-transfer coupling matrix elements and molecular dynamics (MD) to do the thermal averaging. Using an incoherent transport model we calculate a hole mobility of 6.5 cm2/(V s) for pentacene crystals at 300 K. This can be compared to recent experimental results of 5 cm2/(V s). However, we find that an alternative packing into the crystal could lead to a hole mobility of 15.2 cm2/(V s). This suggests that current materials might still be improved by a factor of ∼3. Such calculations might be useful for finding solid-state structures that would increase the hole mobility for use in high-performance molecular devices.

Ab initio Hartree–Fock study of electron transfer in organic molecules

Electron transfer (ET) in σ-bonded organic cage structures (bicyclo[1.1.1]pentane, cubane, and bicyclo[2.2.2]octane) has been studied with the help of ab initio Hartree–Fock calculations in the framework of a two-state model. The calculated values of the ET coupling matrix element VAB exhibit strong dependence on the basis set employed. A minimal basis set underestimates the value of VAB with respect to an extended (double-zeta and polarization) basis set. The ET shows correlation with the electronic and geometrical structure of the molecules studied. It is found that the more strained the chemical bonds in the cage structure are, the stronger is the coupling between the two states participating in ET. Furthermore, the ET matrix element VAB is calculated to have its maximum value when the two end groups attached to the cage structures are coplanar, and its minimum value when two end π groups are perpendicular to each other. However, for coplanar end-groups, minimal changes are noted in the value of VAB with respect to the rotation of the σ-bonded cage. The dependence of ET on the relative orientation of the planes of the end groups offers a mechanism for designing molecular switches.

Coupling matrix element of electron self‐exchange reactions in solution

AbstractOn the basis of the common feature among the electron transfer process and the ion hydration process as well as the relevant experimental kinetic data of electron trader reaction, a new accurate hydration potential function scheme for the determination of electron transfer coupling matrix element is presented. The coupling matrix element between two hydrated ions of the reacting system in solution is calculated. The results and the applicability of this scheme are discussed.

Direct evaluation of the electron transfer integral for self-exchange reactions in solution

This paper presents several new theoretical schemes for experimentally determining the electronic coupling matrix element of the self-exchange electron transfer reactions between hydrated redox ion pairs in solution by using the experimental electron transfer rate data. The activation energies are determined by using a new hydration potential function model proposed here in which the potential energy surfaces are obtained by fitting the relevant thermodynamic data with an analytical function. The results have shown that the accurate and approximate schemes in the limit of weak electronic coupling are very valid in determining the electron transfer coupling matrix element of the self-exchange reactions in solution. Although inclusion of the Newton approximation may slightly decrease the values of the coupling matrix element, they are still in good agreement with those from the accurate method and the other theoretical methods. The implication that the value of the coupling matrix element is small for this system (<100 cm −1) is that the electron transfer reactions between the hydrated ion pairs in solution are nonadiabatic in nature.

Theoretical Studies of Electron Transfer and Electron Localization at the Semiconductor−Liquid Interface

We present new models and simulations of electron transfer (ET) at the semiconductor−liquid interface (SLI). The simulations are of a “first principles” molecular dynamics type and therefore incorporate electronic structure calculations. An In(H2O)62+/3+ redox species, water, and InP semiconductor system are focused on. We discuss the problem of electron localization at this interface, especially as it relates to ET. The study allows the mechanism of the ET process to be analyzed. Rate constant calculations are performed with the dynamics of the entire system incorporated. We apparently present the first calculation of electron transfer coupling matrix elements for the SLI.