Marcus Theory Of Electron Transfer Research Articles

Bridge-Length- and Solvent-Dependent Charge Separation and Recombination Processes in Donor-Bridge-Acceptor Molecules.

The photoinduced intramolecular charge separation (CS) and charge recombination (CR) phenomena in a series of donor-bridge-acceptor (D-B-A) molecules are intensively investigated as a means of understanding electron transport through the π-B. Pyrene (Pyr) and triarylamine (TAA) moieties connected via phenylene Bs of various lengths are studied because their CS and CR behaviors can be readily monitored in real time by femtosecond transient absorption (fs-TA) spectroscopy. By combining the steady-state and fs-TA spectroscopic measurements in a variety of solvents together with chemical calculations, the parameters that govern the CS behaviors of these dyads were obtained, such as the solvent effects on free energy and the B-length-dependent electronic coupling (VDA) between D and A. We observed the sharp switch of the CS behavior with the increase of the solvent polarity and B-linker lengths. Furthermore, in the case of the shortest distance between D and A when the electron coupling is sufficiently large, we observed that the CS phenomenon occurs even in low-polar solvents. Upon increasing the length of B, CS occurs only in strong polar solvents. The distance-dependent decay constant of the CS rate is determined as ∼0.53 Å-1, indicating that CS is governed by superexchange tunneling interactions. The CS rate constants are also approximately estimated using Marcus electron transfer theory, and the results imply that the VDA value is the key factor dominating the CS rate, while the facile rotation of the phenylene B is important for modulating the lifetime of the charge-separated state in these D-B-A dyads. These results shed light on the practical strategy for obtaining a high CS efficiency with a long-lived CS state in TAA-B-Pyr derivatives.

Heat transport induced by electron transfer: A general temperature quantum calculation.

Electron transfer dominates chemical processes in biological, inorganic, and material chemistry. Energetic aspects of such phenomena, in particular, the energy transfer associated with the electron transfer process, have received little attention in the past but are important in designing energy conversion devices. This paper generalizes our earlier work in this direction, which was based on the semiclassical Marcus theory of electron transfer. It provides, within a simple model, a unified framework that includes the deep (nuclear) tunneling limit of electron transfer and the associated heat transfer when the donor and acceptor sites are seated in environments characterized by different local temperatures. The electron transfer induced heat conduction is shown to go through a maximum at some intermediate average temperature where quantum effects are already appreciable, and it approaches zero when the average temperature is very high (the classical limit) or very low (deep tunneling).

Photoinduced electron transfer reactions in mixed micelles of a star block copolymer and surface active ionic liquids: Role of the anion

This work investigates the effect of different counter anions of ionic liquid (IL) co-surfactants, viz. [NTf2]−, [DCN]−, [PF6]−, [BF4]−, [Br]−, associated with the common cation (1-decyl-3-methylimidazolium, [DMIm]+), on the microenvironments of mixed micelles formed with a star block copolymer, T1304, through spectrofluorometric studies. The role of IL anions has been explored for modulating photoinduced electron transfer (PET) reactions between a series of coumarin dyes as the electron acceptors and N,N-dimethylaniline (DMAN) as the electron donor in different T1304-IL mixed micelles. It is revealed that IL co-surfactants increase the polarity in the corona region of micelles to different extents, depending on the nature of the IL anion. The PET reactions in all micellar systems follow the Marcus Inversion (MI) behavior, as predicted by Marcus electron transfer theory, but the rate constant of electron transfer and the onset of the MI along the reaction exergonicity scale, (−ΔG°)onset, varies with the IL anion. It is observed that rather than being correlated with their chaotropic/kosmotropic nature, the effect of the IL in T1304 micelles can be correlated with the hydrophobicity/hydrophilicity, and the steric bulkiness of the IL anions.

Theoretical studies on photo-induced electron transfer process on [Thioridazine].C60 nano-complex; a first principle DFT and TD-DFT

In this study, using the density functional theory (DFT) and time dependent density functional theory (TD-DFT) methods, the physical and chemical properties of the Thioridazineand fullerene C60 nano complex were studied. The most important goal was increasing C60 dipolar moment as a novel drug delivery system to carry Thioridazineand. Several descriptors were used in the ground state, including electrochemical properties based on the HOMO and LUMO orbital energy, hardness, softness, chemical potential, and Mulliken charge. The dipole moment of this nano-complex is about 2.61D, which indicates its moderate solubility in polar solvents. The UV-Vis spectrum obtained with the CAM-B3LYP method shows that the absorption spectrum has blue-shifted by about λ = 24 nm after formation of the complex. Based on the calculations in the excited state and the hole-electron theory in the first three modes, a photo-induced electron transfer (PET) phenomenon was observed at different absorption wavelengths for the complex. Using the Marcus theory of electron transfer, the free energy of activation for electron transfer and the free energy of electron transfer for all PETs were calculated.

Interrogation of O-ATRP Activation Conducted by Singlet and Triplet Excited States of Phenoxazine Photocatalysts.

Organocatalyzed ATRP (O-ATRP) is a growing field exploiting organic chromophores as photoredox catalysts (PCs) that engage in dissociative electron-transfer (DET) activation of alkyl-halide initiators following absorption of light. Characterizing DET rate coefficients (kact) and photochemical yields across various reaction conditions and PC photophysical properties will inform catalyst design and efficient use during polymerization. The studies described herein consider a class of phenoxazine PCs, where synthetic handles of core substitution and N-aryl substitution enable tunability of the electronic and spin characters of the catalyst excited state as well as DET reaction driving force (ΔGET0). Using Stern-Volmer quenching experiments through variation of the diethyl 2-bromo-2-methylmalonate (DBMM) initiator concentration, collisional quenching is observed. Eight independent measurements of kact are reported as a function of ΔGET0 for four PCs: four triplet reactants and four singlets with kact values ranging from 1.1 × 108 M-1 s-1, where DET itself controls the rate, to 4.8 × 109 M-1 s-1, where diffusion is rate-limiting. This overall data set, as well as a second one inclusive of five literature values from related systems, is readily modeled with only a single parameter of reorganization energy under the frameworks of the adiabatic Marcus electron-transfer theory and Marcus-Savéant theory of DET. The results provide a predictive map where kact can be estimated if ΔGET0 is known and highlight that DET in these systems appears insensitive to PC reactant electronic and spin properties outside of their impact on the driving force. Next, on the basis of measured kact values in selected PC systems and knowledge of their photophysics, we also consider activation yields specific to the reactant spin states as the DBMM initiator concentration is varied. In N-naphthyl-containing PCs characterized by near-unity intersystem crossing, the T1 is certainly an important driver for efficient DET. However, at DBMM concentrations common to polymer synthesis, the S1 is also active and drives 33% of DET reaction events. Even in systems with low yields of ISC, such as in N-phenyl-containing PCs, reaction yields can be driven to useful values by exploiting the S1 under high DBMM concentration conditions. Finally, we have quantified photochemical reaction quantum yields, which take into account potential product loss processes after electron-transfer quenching events. Both S1 and T1 reactant states produce the PC•+ radical cation with a common yield of 71%, thus offering no evidence for spin selectivity in deleterious back electron transfer. The subunity PC•+ yields suggest that some combination of solvent (DMAc) oxidation and energy-wasting back electron transfer is likely at play and these pathways should be factored in subsequent mechanistic considerations.

Bell-Shaped Electron Transfer Kinetics in Gold Nanoclusters.

Although metal nanoclusters (MNCs) have shown great promise for the further development of photochemical techniques to be applied in diverse areas (e.g., photoelectronic devices, photochemical sensors, photocatalysts, and energy storage and conversion systems), the fundamental problem of their electron transfer behavior still remains unsolved. Herein, a driving force-dependent photoinduced electron transfer process of gold nanoclusters (AuNCs) is clarified for the first time from a rational-designed opposite-charged system. It was found that the electron transfer dynamic of carboxylated chitosan and dithiothreitol-commodified AuNCs (CC/DTT-AuNCs) can be satisfactorily described by the Marcus electron transfer theory. This proved model was applied to estimate the ultrafast charge separation process between CC/DTT-AuNCs and mitoxantrone, which was confirmed by fluorescence quenching and femtosecond transient absorption spectroscopy measurements. We envision that this work will open a new door for understanding the electron transfer behavior of MNCs and facilitate the design of advanced optoelectronic devices.

Molecular design of dibenzo[g,p]chrysene-based hole-transporting materials for perovskite solar cells: A theoretical study

Designed with a steric twisted, π-conjugated dibenzochrysene (DBC) core and arylamine-based electron-donating side arms, four small molecules as hole-transporting materials (HTMs) are simulated with density functional theory and Marcus theory of electron transfer. Our results show that, adding the fluorene moiety in auxiliary side arms and extending the π-conjugated structure can make the highest occupied molecular orbital (HOMO) energy levels down-shifted. By tailoring of electron-donating side arms, the HOMO levels of designed HTMs range from −4.95 to −5.24 eV, which affords a chance for the interfacial energy regulation. Meanwhile, we also find that the suitable extension of π-conjugated side arms and the accessorial sulfur-sulfur interaction may be beneficial for promoting the intermolecular electronic coupling. Coupled with the lower reorganization energy, the DBC-4 (7.08 × 10−1 cm2 v−1 s−1) displays the largest hole mobility. In addition, the better solubility can be expected for the DBC-4 due to the larger solvation free energy, whereas its stability may be somewhat lower. Adding thiophene unit in side arms makes the absorption spectra obviously red-shift. Overall, this work provides some useful clues for designing of high-efficient HTMs, and the DBC-4 is proposed as potential HTM.

Chromium isotope fractionation during reduction of Chromium(VI) by Iron(II/III)-bearing clay minerals

Chromium stable isotope ratios are used to trace the reduction of Cr(VI) to Cr(III) in both ancient and modern systems. However, quantitative interpretation of Cr isotopic signatures has been stymied by the large variability in isotopic fractionation factors for Cr(VI) reduction by different reductants. Here we determine Cr isotope fractionation factors during Cr(VI) reduction by Fe(II/III)-bearing clay minerals, which are abundant in subsurface environments. Several variables were tested: pH, total Fe content of the clay, and the fraction of reduced Fe within the clay (Fe(II)/Fe(total)). The latter controls the standard reduction potential of the clay. Our results demonstrate that neither pH nor total Fe content of the clay have major effects on isotopic fractionation. In contrast, as the effective standard reduction potential of the clay and thus the standard free energy of Cr(VI) reduction become more negative, Cr isotope fractionation factors decrease in magnitude from −4.9 to −1.3‰ according to a linear free energy relationship. This linear free energy relationship can be predicted from Marcus electron transfer theory and allows first-order predictions of Cr isotope fractionation factors to be made from the standard reduction potential or Fe(II)/Fe(total) of a clay, potentially improving our ability to model Cr isotope signatures in geochemical systems. Chromium is the first isotope system to show such a linear free energy relationship over a diverse range of reductants, including both aqueous and solid-phase reductants, and may provide a model for determining other redox-driven kinetic isotope effects in environmentally important isotope systems.

Redox Properties of Native and Damaged DNA from Mixed Quantum Mechanical/Molecular Mechanics Molecular Dynamics Simulations

The redox properties of two large DNA fragments composed of 39 base pairs, differing only by an 8-oxoguanine (8oxoG) defect replacing a guanine (G), were investigated in physiological conditions using mixed quantum mechanical/molecular mechanical (QM/MM) molecular dynamics simulations. The quantum region of the native fragment comprised 3 G-C base pairs, while one G was replaced by an 8oxoG in the defect fragment. The calculated values for the redox free energy are 6.55 ± 0.28 eV and 5.62 ± 0.30 eV for the native and the 8oxoG-containing fragment, respectively. The respective estimates for the reorganization free energy are 1.25 ± 0.18 eV and 1.00 ± 0.18 eV. Both reactions follow the Marcus theory for electron transfer. The large difference in redox potential between the two fragments shows that replacement of a G by an 8oxoG renders the DNA more easily oxidizable. This finding is in agreement with the suggestion that DNA fragments containing an 8oxoG defect can act as sinks of oxidative damage that protect the rest of the genome from assault. In addition, the difference in redox potential between the native and the defect DNA fragment indicates that a charge transfer-based mechanism for the recognition of DNA defects might be feasible, in line with recent suggestions based on experimental observations.

Mechanistic Insight into Concerted Proton-Electron Transfer of a Ru(IV)-Oxo Complex: A Possible Oxidative Asynchronicity.

We have thoroughly investigated the oxidation of benzyl alcohol (BA) derivatives by a RuIV(O) complex (RuIV(O)) in the absence or presence of Brønsted acids in order to elucidate the proton-coupled electron-transfer (PCET) mechanisms in C-H oxidation on the basis of a kinetic analysis. Oxidation of BA derivatives by RuIV(O) without acids proceeded through concerted proton-electron transfer (CPET) with a large kinetic isotope effect (KIE). In contrast, the oxidation of 3,4,5-trimethoxy-BA ((MeO)3-BA) by RuIV(O) was accelerated by the addition of acids, in which the KIE value reached 1.1 with TFA (550 mM), indicating an alteration of the PCET mechanism from CPET to stepwise electron transfer (ET) followed by proton transfer (PT). Although the oxidized products of BA derivatives were confirmed to be the corresponding benzaldehydes in the range of acid concentrations (0-550 mM), a one-electron-reduction potential of RuIV(O) was positively shifted with increases in the concentrations of acids. The elevated reduction potential of RuIV(O) strongly influenced the PCET mechanisms in the oxidation of (MeO)3-BA, changing the mechanism from CPET to ET/PT, as evidenced by the driving-force dependence of logarithms of reaction rate constants in light of the Marcus theory of ET. In addition, dependence of activation parameters on acid concentrations suggested that an oxidative asynchronous CPET, which is not an admixture of the CPET and ET/PT mechanisms, is probably operative in the boundary region (0 mM < [TFA] < 50 mM) involving a one-proton-interacted RuIV(O)···H+ as a dominant reactive species.

Charge Transfer through Redox Molecular Junctions in Nonequilibrated Solvents.

Molecular conduction operating in dielectric solvent environments is often described using kinetic rates based on the Marcus theory of electron transfer at a molecule-metal electrode interface. However, the successive nature of charge transfer in such a system implies that the solvent does not necessarily reach equilibrium in such processes. Here we generalize the theory to account for solvent nonequilibrium and consider a molecular junction consisting of an electronic donor-acceptor system coupled to two metallic electrodes and placed in a polarizable solvent. We determine the nonequilbrium distribution of the solvent by solving diffusion equations in the strong- and weak-friction limits and calculate the charge current and its fluctuating behavior. In extreme limits, the absence of the solvent or fast solvent relaxation, the charge-transfer statistics is Poissonian, while it becomes correlated by the dynamic solvent between these limits. A Kramers-like turnover of the nonequilibrium current as a function of the solvent damping is found. Finally, we propose a way to tune the solvent-induced damping using geometrical control of the solvent dielectric response in nanostructured solvent channels.

Positional Effect of the Triphenylamine Group on the Optical and Charge-Transfer Properties of Thiophene-Based Hole-Transporting Materials.

Hybrid organic-inorganic perovskite solar cells (PSCs) have shown significant potential for use in the energy field. Typically, hole-transporting materials (HTMs) play an important role in affecting the power conversion efficiency (PCE) of PSCs. A deep understanding of the structure-property relationship plays a vital role in developing efficient HTMs. Herein, the relationship between the structure and properties of two small organic HTMs H2,5 and H3,4 were systematically investigated in terms of the electronic and optical properties, the hole-transporting behavior by using density functional theory (DFT) and Marcus electron transfer theory. The results demonstrated that the high power conversion efficiency of the H2,5-based PSC was caused by strong interactions with the perovskite material on the interface and an enhanced hole mobility in H2,5 compared with H3,4. The strong interaction derives from the short bond length of O atom of HTM and Pb atom of perovskite material, and the highly hole mobility derives from the quasi-planar conjugated conformation and tight packing model of neighboring molecules in H2,5. In addition, we found that the planar structure enhances the intermolecular interaction between HTM and perovskite materials compared with the 'V'-shaped molecule. Importantly, we also note that the HOMO level of the isolated molecule is not always proportional to the open-circuit voltages of PSCs since the HOMO level might move toward a higher level when the interaction between HTM and interface of perovskite was included. The work gives essential information for rational designing efficient HTMs.

Tuning Electron-Transfer Reactivity of a Chromium(III)–Superoxo Complex Enabled by Calcium Ion and Other Redox-Inactive Metal Ions

Calcium ion plays an indispensable role for water oxidation by oxygen-evolving complex (OEC) composed of a manganese-oxo cluster (Mn4CaO5) in Photosystem II. In this context, the effects of Ca2+ ion and other redox-inactive metal ions on the redox reactivity of high-valent metal-oxo and metal-peroxo complexes have been studied extensively. Among metal-oxygen intermediates involved in interconversion between H2O and O2, however, the effects of Ca2+ ion and other redox-inactive metal ions (Mn+) on the redox reactivity of metal-superoxo complexes have yet to be reported. Herein, we report that electron transfer (ET) from octamethylferrocene (Me8Fc) to a mononuclear nonheme Cr(III)-superoxo complex, [(Cl)(TMC)CrIII(O2)]+ (1), occurs in the presence of redox-inactive metal ions (Mn+ = Ca2+, Mg2+, Y3+, Al3+, and Sc3+); in the absence of the redox-inactive metal ions, ET from Me8Fc to 1 does not occur. The second-order rate constants (ket) of ET from Me8Fc to 1 in the presence of a redox-inactive metal ion increased with increasing concentration of Mn+ ([Mn+]), exhibiting a second-order dependence on [Mn+]: ket = kMCET[Mn+]2, where kMCET is the fourth-order rate constant of metal ion-coupled electron transfer (MCET). This means that two Mn+ ions are bound to the one-electron reduced species of 1. Such a binding of two Mn+ ions associated with the ET reduction of 1 resulted in a 92 mV positive shift of the one-electron reduction potential of 1 (Ered) with increasing log([Mn+]). The log kMCET values increased linearly with the increasing Lewis acidity of Mn+ (ΔE), which was determined from the g values of O2•--Mn+ complexes. The driving force dependence of log ket of MCET from ferrocene derivatives to 1 in the presence of Mn+ has been well-evaluated in light of the Marcus theory of electron transfer.

Photoinduced Ultrafast Electron Transfer and Charge Transport in a PbI2/C60 Heterojunction

Charge transport and electron transfer in a PbI2/C60 heterojunction were investigated. The charge carrier mobilities and trap densities of PbI2 were extracted from current–voltage characteristics of hole- and electron-only devices. Femtosecond transient absorption spectroscopy was used to elucidate the photophysical processes occurring in the heterojunction. For a pristine PbI2 film, trap-limited bimolecular recombination was the dominant mechanism in the case of low pump fluence. We observed photoinduced ultrafast electron transfer from PbI2 to C60 with a rate constant of 0.45 ps–1. Semiclassical Marcus electron transfer theory was used to estimate the electronic coupling between the conduction band edge of PbI2 and the lowest unoccupied molecular orbital of C60. We also fabricated a solar cell using the PbI2/C60 heterojunction. Electron transfer and charge extract efficiencies in our cell were also deduced. The performance-limiting factors for solar cells based on PbI2 were discussed and a strategy to improve the device performance was developed. Our work is useful for ultraviolet-harvesting transparent solar cells and other photophysical and photochemical applications.

A model for kinetic isotope fractionation during redox reactions

Stable isotopes are used to track redox reactions in both ancient and modern geochemical systems. However, because the magnitude and even the direction of fractionation depend on the reaction pathway, extracting information about redox conditions from isotopic signatures is difficult. Quantitative understanding of the fundamental thermodynamic controls on redox-driven fractionation may improve the reliability of fractionation models in natural systems. Here we develop a mechanistic framework based on Marcus electron transfer theory to model redox-driven kinetic isotope fractionation as a function of the corresponding equilibrium fractionation and thermodynamic parameters. The framework predicts that for related reactions, (1) kinetic fractionation during electron transfer should be proportional to and in the same direction as equilibrium fractionation and (2) the magnitude of kinetic fractionation should decrease linearly as the standard free energy of the reaction decreases and the reaction becomes more thermodynamically favorable. Furthermore, kinetic fractionation should be log-linearly correlated with the rate constant of electron transfer, such that a faster redox reaction induces less kinetic fractionation. To illustrate the application of the model to stable isotope systems, we discuss examples of kinetic isotope fractionation during reduction of chromium (VI) and nitroaromatics by aqueous and solid-phase reductants respectively. For both these systems, altering the standard reduction potential of the reductant to vary the standard free energy of the redox reaction produces large changes in the magnitude of kinetic fractionation, which can be quantitatively predicted with our model. The proposed framework thus may be valuable for modeling redox-driven kinetic isotope fractionation in a broad range of geochemically relevant systems for both traditional light stable isotopes (e.g., nitrogen) and nontraditional metal isotopes (e.g., chromium).

Probing impacts of π-conjugation and multiarm on the performance of two-dimensionally expanded small molecule hole-transporting materials: A theoretical investigation

Apart from the spiro-like molecule architecture, a large number of two-dimensionally expanded small molecule hole-transporting materials (HTMs) have been investigated to improve their electronic, optical and charge transport properties. Compared with the variety of synthesized molecules, the systemic studies on the effects of molecular geometry are still less reported. To further explore the useful clues for the rational design of two-dimensional small molecule materials, a series of new designed (4–8) and the model (1–3) HTMs are simulated by combining of the density functional theory and the Marcus theory of electron transfer. Our results show that, by adding oxygen-bridge in the core unit and additional electron-donor, the highest occupied molecular orbital (HOMO) levels of designed HTMs are slightly up-shifted, whereas introducing carbon-carbon single bond makes the HOMOs more stabilized due to the slight break of molecular π-conjugation. Meanwhile, by rigidifying and extending the π-conjugated core structure and adding of extra electron-donors, the reorganization energies are obviously lowered and the transfer integrals are increased. Accordingly, the hole mobilities of designed HTMs are distinctly enlarged. Moreover, our results also indicate that the weak light absorption in visible region, easy charge dissociation, and good solubility and stability can be expected for these designed molecules, and we hope that our results could be helpful for the design of high-efficient HTMs.

Regioselective Oxybromination of Benzene and Its Derivatives by Bromide Anion with a Mononuclear Nonheme Mn(IV)-Oxo Complex.

Oxybromination of aromatic compounds by high-valent metal-oxo intermediates has yet to be explored despite extensive studies on the oxybromination of aliphatic C-H bonds of hydrocarbons. Herein, we report the regioselective oxybromination of methoxy-substituted benzenes by a nonheme MnIV-oxo complex binding scandium ions, [(Bn-TPEN)MnIV(O)]2+-(Sc(OTf)3)2 (1), in the presence of tetrabutylammonium bromide. The regioselective oxybromination occurs at the carbon atom with the highest positive charge via electron transfer (ET) from the methoxy-substituted benzenes to 1. ET driving force dependence of the rate constants of ET from methoxy-substituted benzenes to 1 is well fitted in light of the Marcus theory of ET. Under photoirradiation, the oxybromination of benzene by 1 can be achieved via ET from benzene to the photoexcited state of 1, although no reaction occurs between benzene and the ground state of 1 in the dark. To the best of our knowledge, this is the first example of reporting the stoichiometric regioselective oxybromination of the benzene ring by a synthetic high-valent Mn(IV)-oxo complex and the catalytic regioselective oxybromination reaction with a Mn(II) complex and a terminal oxidant.

Small Reorganization Energy for Ligand-Centered Electron-Transfer Reduction of Compound I to Compound II in a Heme Model Study

The electron-transfer (ET) processes from electron-donor substrates to oxoiron(IV) porphyrin π-cation-radical species (Cpd I) are key steps in their oxygenation reactions. Here, we have evaluated the rate constants of the outer-sphere ET reduction of Cpd I model complexes of meso-tetramesitylporphyrin (1) and 2,7,12,17-tetramesityl-3,8,13,18-tetramethylporphyrin (2) in light of the Marcus theory of ET to determine the ET reorganization energies (λ). The λ values of the ligand-centered ET reduction of Cpd I model complexes are much smaller than those of the metal-centered ET reduction of various oxoiron(IV) complexes. Moreover, the λ value of 1 is larger than that of 2, resulting from the difference in the nature of the a1u/a2u porphyrin π-cation-radical orbitals.

Effect of mono-halogen-substitution on the electron transporting properties of perylene diimides: A density functional theory study

Density functional theory and Marcus electron transfer theory were used to explore the electron transporting properties of a series of mono-halogenated perylene diimides X-PDI (X = F, Cl, Br), as well as their parent compound H-PDI. The electronic structures, absorption spectra, electron mobility, and adsorption properties were investigated. It is found that the theoretically simulated absorption spectra reproduce very well the experimentally available data. The predicted electron mobilities follow the order of F-PDI < H-PDI < Cl-PDI ≈ Br-PDI, which is in accordance with the experimental trend. Furthermore, our theoretically designed molecule Cl-PDI exhibits good hydrophobicity, stability and solubility. Importantly, the electron mobility of Cl-PDI is very similar as that of Br-PDI. Considering that mono-bromine-substituted perylene diimide Br-PDI has been observed to be an excellent electron transporting material in inverted perovskite solar cell, mono-chlorine-substitution Cl-PDI is also expected to be a potential ETM.

Mechanistic Theoretical Investigation of Self-Discharge Reactions in a Vanadium Redox Flow Battery.

Compared to the studies of new electrolyte and electrode chemistries aimed to push the energy and power density of battery systems, investigations of self-discharge reactions contributing to capacity fading are still very limited, especially at the molecular level. Herein, we present a computational study of oxidation-reduction reactions between vanadium ions in solution leading to battery self-discharge due to the crossover of vanadium species through the membrane in all-vanadium redox flow batteries (RFB). By utilizing Car-Parrinello molecular dynamics (CPMD) based metadynamics simulations in combination with the Marcus electron transfer theory, we examine the energetics of condensation reactions between aqueous vanadium ions to form dimers and their subsequent dissociation into vanadium species of different oxidation states after electron transfer has occurred. Our results suggest that multiple self-discharge reaction pathways could be possible under the vanadium RFB operation conditions. The study underscores the complexity of vanadium polymerization reactions in aqueous solutions with coupled electron and proton transfer processes that can lead to the formation of various mixed-valence vanadium polymeric structures.