均相氧化还原反应中 homo 和 LOMO 能级位置差异引起化学反应速率差异的文献

… rate parameters for outer-sphere electron transfer in heterogeneous and homogeneous … parameters for 11 electrochemical and 45 homogeneous self-exchange and cross reactions …

… The smaller HOMO-LUMO gap for CrF6 than MoF6 is caused both by the strongly oxidizing … accompaning electron transfer, the site of electron transfer, and rates of homogeneous redox …

… are critical in determining transfer rates. Although ET and … HOMOs and LUMOs treated in a balanced manner. Therefore, to calculate the energy gap for a radical cation in a hole transfer …

… Both the heterogeneous and the homogeneous analyses … have essentially the same E and rate constants, respectively. At … In terms of HOMO−LUMO band gap estimates, 4b we obtain …

… of the charge transferred by the sum of their hardnesses [4]. The inverse of hardness, softness [… It should be noted that for a system with a HOMO-LUMO gap, such a derivative is not well …

… to evaluate electronic properties of molecular systems with the IT quantities, we examined their feasibility and applicability to quantify frontier orbital energies and the HOMO/LUMO gap, …

and are largely similar across systems, with the exception of substituents containing lone pairs of electrons that exhibit significant deformation upon electron transfer. Our study therefore suggests that while a wide range of ET rates are observed, there is an upper limit to rate enhancements achievable by only tuning the substituent electrophilicity.

… The temperature-dependent kinetics of electron transfer is characterized in classical Marcus … MV systems have different oxidation states at two redox centers in the same molecule. An …

… Abstract Applying density functional theory (DFT)-based … Total energies ER and EO are calculated at the level of DFT for … of the electron in state R (HOMO) and full electronic relaxation …

… orbital energies and the chemical reactions.16 Plotting the global hardness responses, the halves of the HOMO-LUMO … (T) reaction barrier energies and experimental rate constants for …

… on the favorable intermolecular HOMO−LUMO interaction of the … This background led to the development of redox-mediated … through redox control of the intermolecular HOMO−LUMO …

… considered in this work is the computational cost per point. To create a fast … energy or electron affinity. Linear relationship between HOMO and LUMO energies and oxidation/reduction …

Abstract The reaction between superoxide (O2•−) and organic chemicals is of interest in many scientific disciplines including biology and synthetic chemistry, as well as for the evaluation of chemical fate in the environment. Due to limited data and lack of congeneric modelling, the involvement of superoxide in many complex processes cannot be adequately evaluated. In this study, we developed new quantitative structure–property relationship (QSPR) models for the prediction of the aqueous-phase rate constant for the reaction between superoxide and a wide variety of organic chemicals reacting via one-electron oxidation, reduction and hydrogen-transfer. It is shown that the relative importance of these pathways is related to frontier molecular orbital (FMO) interaction and to pH. The class-specific QSPRs developed have good statistics (0.84 ≤ R2 ≤ 0.92). For non-congeneric chemicals it is demonstrated that the reactivity toward superoxide can be described by applying explicit descriptions for competition kinetics and speciation. Therefore, the relationships developed in this study are useful as a starting point to evaluate more complex molecules having, for example, multiple reactive functional groups, labile H bonds, or delocalised cationic charges. However, additional kinetic data and more rigorous computation are needed to evaluate such molecules.

… redox reaction between the copper and sugar molecules. In chemistry, HOMO and LUMO are known as frontier orbitals … There was a difference in the reaction rate between ketose and …

… (5-9) SO 4 •– is a strong one-electron oxidant with a redox … quantum chemical descriptors (E HOMO , E LUMO , E LUMO –E … based on E LUMO –E HOMO , indicates the reaction rates at …

… prediction of the distance dependence of electron transfer reactions - ScienceDirect … of electron exchange reactions is a sensitive function of the donor–bridge energy gap and bri…

Significance Nature’s use of electronic coupling (HDA) and free-energy (ΔGo) gradients to vectorially control electron transport provides inspiration for artificial photosynthesis. Theoretical predictions indicate that HDA and ΔGo are not independent parameters, and are instead linked. Reported here is a broadly applicable kinetic approach that was utilized to demonstrate such behavior for four acceptor–bridge–donor compounds. When the electronic coupling was large and electron transfer was adiabatic, the free energy of the reaction |ΔGo| was less than that for nonadiabatic transfer. This finding should be taken into account in the design of hybrid materials for solar energy conversion and has broad implications to the many classes of electron-transfer reactions in biology and chemistry. Electron-transfer theories predict that an increase in the quantum-mechanical mixing (HDA) of electron donor and acceptor wavefunctions at the instant of electron transfer drives equilibrium constants toward unity. Kinetic and equilibrium studies of four acceptor–bridge–donor (A-B-D) compounds reported herein provide experimental validation of this prediction. The compounds have two redox-active groups that differ only by the orientation of the aromatic bridge: a phenyl–thiophene bridge (p) that supports strong electronic coupling of HDA > 1,000 cm−1; and a xylyl–thiophene bridge (x) that prevents planarization and decreases HDA < 100 cm−1 without a significant change in distance. Pulsed-light excitation allowed kinetic determination of the equilibrium constant, Keq. In agreement with theory, Keq(p) were closer to unity compared to Keq(x). A van’t Hoff analysis provided clear evidence of an adiabatic electron-transfer pathway for p-series and a nonadiabatic pathway for x-series. Collectively, the data show that the absolute magnitude of the thermodynamic driving force for electron transfers are decreased when adiabatic pathways are operative, a finding that should be taken into account in the design of hybrid materials for solar energy conversion.

A novel theoretical methodology is proposed to estimate the magnitude of internal reorganization energy for electron transfer and charge recombination processes in donor-bridge-acceptor (D-B-A) type molecular dyads. The potential energy surface for each process is plotted for the shortest path by assuming a displaced but slightly distorted harmonic oscillator model. Structural changes occurring upon photoexcitation and ionization were exploited to calculate the activation energies needed for electron transfer reactions with the aid of involved vibrational modes. D-B-A dyads consisting of octathiophene (T8) paired with three (di)imide acceptors (naphthalene diimide (NDI), benzene diimide (BDI), and naphthalimide (NI)) were studied as model systems for theoretical calculations. It has been found that T8NDI and T8BDI possess very low activation energies for both forward electron transfer and charge recombination, and hence the rates for relevant processes should be very rapid. In contrast, the activation energies for such processes for T8NI were found to be relatively large, and free energy estimations predict that the charge recombination mechanism in T8NI falls into the inverted regime of Marcus semiclassical electron transfer theory. All of the calculated properties of the dyads are in very good agreement with the available experimental data, suggesting the suitability of the proposed theoretical approach in revealing the photoinduced electron transfer mechanisms of molecular dyads.

… electron transfer. DFT calculations revealed that increasing the torsion angle enlarges the HOMO–LUMO energy gap … excitation energy E IT and smallest thermal activation energy ΔG*, …

Long-range electron transfer may occur via two fundamentally different mechanisms depending on the combination of electron donor, acceptor, and the bridging medium between the two redox partners. Activating the so-called hopping mechanism requires matching the energy levels of the donor and the bridge. If electrons from the donor can thermodynamically access bridge-localized redox states, the bridge may be temporarily reduced before the electron is forwarded to the acceptor. As a result, electron transfer rates may demonstrate an extremely shallow dependence on distance. When transient reduction of the bridging medium is thermodynamically impossible, a tunneling mechanism that exponentially depends on distance becomes important for electron transport. Fifty years ago, superexchange theory had already predicted that electron transfer rates should be affected by donor-bridge-acceptor energetics even in the tunneling regime, in which the energy gap (Δε) is too large for electrons to hop from the donor onto the bridge. However, because electron tunneling rates depend on many parameters and the influence of donor-bridge energy gaps is difficult to distinguish from other influences, direct experimental support for the theoretical prediction has been difficult to find. Because of remarkable progress, particularly in the past couple of years, researchers have finally found direct evidence for the long-sought but elusive tunneling-energy gap effect. After a brief introduction to the theory of the tunneling mechanism, this Account discusses recent experimental results describing the importance of the tunneling-energy gap. Experimental studies in this area usually combine synthetic chemistry with electrochemical investigations and time-resolved (optical) spectroscopy. For example, we present a case study of hole tunneling through synthetic DNA hairpins, in which different donor-acceptor couples attached to the same hairpins resulted in tunneling rates with significantly different dependences on distance. Recent systematic studies of conjugated molecular bridges have demonstrated the same result: The distance decay constant (β), which describes the steepness of the exponential decrease of charge tunneling rates with increasing donor-acceptor distance, is not a property of the bridge alone; rather it is a sensitive function of the entire donor-bridge-acceptor (D-b-A) combination. In selected cases, researchers have found a quantitative relationship between the experimentally determined distance decay constant (β) and the magnitude of the tunneling-energy gap (Δε). The rates and efficiencies of charge transfer reactions occurring over long distances are of pivotal importance in light-to-chemical energy conversion and molecular electronics. Tunneling-energy gap effects play an intriguing role in the formation of long-lived charge-separated states after photoexcitation: The kinetic stabilization of these charge-separated states frequently exploits the inverted driving-force effect. Recent studies indicate that tunneling-energy gap effects can differentiate the distance dependences of energy-storing charge-separation reactions from those of energy-wasting charge-recombination processes. Thus, the exploitation of tunneling-energy gap effects may provide an additional way to obtain long-lived charge-separated states.

A unified theory of homogeneous and electrochemical electron-transfer rates is developed using statistical mechanics. The treatment is a generalization of earlier papers of this series and is concerned with seeking a fairly broad basis for the quantitative correlations among chemical and electrochemical rate constants predicted in these earlier papers. The atomic motions inside the inner coordination shell of each reactant are treated as vibrations. The motions outside are treated by the ``particle description,'' which emphasizes the functional dependence of potential energy and free energy on molecular properties and which avoids, thereby, some unnecessary assumptions about the molecular interactions.

… donor and acceptor as a uniform medium, the electronic coupling (and the probability for … The energy gap between HOMO and LUMO in the heme is between —11.4 and—9.7 eV and …

… gap between non-adiabatic ab initio simulations and model approaches such as the Marcus theory. … From now on, we consider one orbital wm (HOMO or LUMO) per fragment, instead of …

… between the HOMO of the donor and the LUMO of the … ISM and Marcus theory: ( 1 ) Marcus theory assumes that the … mol-l; (2) Marcus theory calculates the internal reorganization energy …

… rate, stability, and optoelectronic properties. Different π-linkers have resulted in smaller HOMO-LUMO energy gap … The reorganization energy analysis predicted the ambipolar behavior …