Electron Transfer and Electron Excitation Processes in 2,5-Diaminoterephthalate Derivatives with Broad Scope for Functionalization

Derivatives of 2,5-diaminoterephthalate (DAT) are efficient fluorescence dyes that are also redox-active, thus allowing for the electrochemical manipulation of spectral properties. The electrochemical behaviour of seven DAT derivatives was studied by cyclic voltammetry in dichloromethane. In the absence of a proton donor, DATs should be oxidized in two one-electron steps. The first step is usually quasi-reversible while the second step is either quasi-reversible or irreversible. Some electrochemical properties such as the formal potentials and the ratio between the anodic and the cathodic current were determined from the cyclic voltammograms. Correlation between the formal potential of first oxidation and the absorption or the fluorescence emission wavelengths are established for this specific type of dyes. These correlations were confirmed with density functional theory calculations.     

Benzidine Derivatives: A Class of High Redox Potential Molecules for Aqueous Organic Flow Batteries

The development of water-soluble redox-active molecules with high potentials is one of the effective ways to enhance the energy density of aqueous organic flow batteries (AOFBs). Herein, a series of promising N-substituted benzidine analogues as water-soluble catholyte candidates with controllable redox potentials (0.78–1.01 V vs. standard hydrogen electrode (SHE)) were obtained by the molecular engineering of aqueous irreversible benzidines. Theoretical calculations reveal that the redox potentials of these benzidine derivatives in acidic solution are determined by their electronic structure and alkalinity. Among these benzidine derivatives, N,N,N′,N′-tetraethylbenzidine(TEB) shows both high redox potential (0.82 V vs. SHE) and good solubility (1.1 M). Pairing with H₄[Si(W₃O₁₀)₄] anolyte, the cell displayed discharge capacity retention of 99.4 % per cycle and a high coulombic efficiency (CE) of ∼100 % over 1200 cycles. The stable discharge capacity of 41.8 Ah L⁻¹ was achieved at the 1.0 M TEB catholyte with a CE of 97.2 % and energy efficiency (EE) of 91.2 %, demonstrating that N-substituted benzidines could be promising for AOFBs.     

A voltammetric study of some tris(trimethylsilyl)-methyltin derivatives

Classical d.c. polarography, supplemented by other voltammetric techniques, is used to elucidate the mechanism of reduction of di- and tri-halide derivatives of tris(trimethylsilyl) methyltm, despite the difficulties encountered in work at very negative potentials in ethanolic solutions. The dihalides are reduced in two irreversible one-electron steps; the trihalides are reduced in three one-electron steps, the first of which is quasi-reversible, the other two being irreversible. The first step in each case is adsorption-controlled while the others are diffusion-controlled. D.c. polarography is suitable for the determination of these compounds down to 5 × lO^-5 M.     

Synthesis,electrochemistry and IR spectroelectrochemistry of bisferrocenyl bridged benzene derivates

Two novel biferrocenylcarboxylate benzene derivatives, namely, 1,4-bis(2-Ferrocenecarboxylate) benzene (Fc₂B) and 1,4-bis(2-Ferrocenecarboxylate)-2′-methylbenzene (Fc₂M), have been synthesized. The as-prepared complexes have been confirmed by IR, ¹H NMR and MS. The electron transfer mechanisms of the two compounds and the other three bisferrocenyl bridged benzene complexes, 1,4-disferrocenyl benzene (Fc₂P), 1,4-bis(2-ferrocenylvinyl) benzene (Fc₂E), and 1,4-bis(2-ferrocenylacetyleneyl) benzene (Fc₂Q), have been studied by cyclic voltammetry (CV), in situ difference FT-IR (SNFTIR), and rapid-scan time-resolved FT-IR spectroelectrochemistry (RS-TRS FT-IR). The CV results suggest that the redox formal potentials of the five bridged complexes are depended on their bridged groups and abilities of withdrawing electron. IR absorption peaks arisen from intermediate appearance and disappearance in the oxidation and reduction process of Fc₂B, Fc₂E, Fc₂P and Fc₂Q were clearly observed by the in situ rapid-scan or SNFTIR spectroelectrochemistry. The results indicated the redox process of the four bisferrocenyl bridged benzene complexes involved two consecutive one-electron steps. Although the intermediate peak of Fc₂M was not observed by in situ FT-IR spectroelectrochemistry, we still thought the redox process of Fc₂M could involve two consecutive one-electron steps.     

Theoretical study on redox potentials of organic radicals in different solvents

The BMK density functional theory method has been used to examine the redox potentials of organic radicals in different solvents (DMF, N,N-dimethylformamide; DMSO, dimethyl sulfoxide; MeCN, acetonitrile). The polarizable continuum solvation model (PCM) was used to describe the solvation-free energies. The one-electron electrochemical standard potentials (E ⁰) of ca. 100 organic radicals in three solvents were calculated using a single, unified theoretical method whose reliability has been tested against almost all the available experimental data. It was found that the mean absolute deviation (MAD) between the theory and experiment was about 0.08 V. With the newly developed theoretical method in hand, more redox potentials of organic radicals in these three solvents were predicted by this single, unified method. The results showed that the redox potentials of organic radicals in different organic solvents including DMF and DMSO had good correlations with their redox potentials in MeCN.     

Electrochemical reduction of 3,3′-bi(2-R-5,5-dimethyl-4-oxopyrrolinylidene)-1,1′-dioxides in water and its binary mixtures with acetonitrile

It has been shown by cyclic voltammetry for the first time for nitrons that the first step of electrochemical reduction of 3,3′-bi(2-R-5,5-dimethyl-4-oxopyrrolinylidene)-1,1′-dioxides in water and its binary mixtures with acetonitrile is a reversible one-electron process. The potentials of the first one-electron reduction peaks shift toward less negative values with an increase in the water content in the binary mixture, being in water equal to −0.14, −0.09, −0.08, and +0.19 V vs. saturated calomel electrode for dinitrons with R = Me, Ph, Bu^t, and CF₃, respectively. Such very low reduction potentials allow one to use derivatives of these dinitrons as redox-active labels in applied bioorganic electrochemistry. Dedicated to the memory of Academician N. N. Vorozhtsov on the 100th anniversary of his birth. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1227–1229, June, 2007.     

Tuneable Redox Chemistry and Electrochromism of Persistent Symmetric and Asymmetric Azine Radical Cations

Molecular organic radicals have been intensively studied in the last decades, due to their interesting optical, magnetic and redox properties. Here we report the synthesis and characterisation of persistent organic radicals from one-electron oxidation of redox-active azines (RAAs), composed of two guanidinyl or related groups. By connecting two different groups together, asymmetric compounds result. In this way a series of compounds with varying redox potential is obtained that could be oxidised reversibly to the mono- and the dicationic charge states. The accessible redox states were fully determined by chemical redox reactions. The standard Gibbs free energy change for disproportionation of the radical monocation into the dication and the neutral molecule in solution, estimated from cyclovoltammetric measurements, varies between 43 and 71 kJ mol⁻¹. While the neutral RAAs absorb predominately UV light, the radical monocations display strong absorptions covering almost the entire visible region and extending for some compounds into the NIR region. A detailed analysis of this highly reversible electrochromism is presented, and the fast switching characteristics are demonstrated in an electrochromic test device.     

Uranyl-Bound Tetra-Dentate Non-Innocent Ligands: Prediction of Structure and Redox Behaviour Using Density Functional Theory

Computational methods have been applied to understand the reduction potentials of [UO₂-salmnt-L] complexes (L=pyridine, DMSO, DMF and TPPO), and their redox behavior is compared with previous experiments in dichloromethane solution. Since the experimental results were inconclusive regarding the influence of the uranyl-bound tetra-dentate ‘salmnt’ ligand, here we will show that salmnt acts as a redox-active ligand and exhibits non-innocent behavior to interfere with the otherwise expected one-electron metal (U) reduction. We have employed two approaches to determine the uranyl (VI/V) reduction potentials, using a direct study of one-electron reduction processes and an estimation of the overall reduction using isodesmic reactions. Hybrid density functional theory (DFT) methods were combined with the Conductor-like Polarizable Continuum Model (CPCM) to account for solvation effects. The computationally predicted one-electron reduction potentials for the range of [UO₂-salmnt-L] complexes are in excellent agreement with shoulder peaks (∼1.4 eV) observed in the cyclic voltammetry experiments and clearly correlate with ligand reduction. Highly conjugated pi-bonds stabilize the ligand based delocalized orbital relative to the localized U f-orbitals, and as a consequence, the ligand traps the incoming electron. A second reduction step results in metal U(VI) to U(V) reduction, in good agreement with the experimentally assigned uranyl (VI/V) reduction potentials.     

Optoelectronic Properties of Carbon-Bound Boron Difluoride Hydrazone Dimers

The creation of dimeric boron difluoride complexes of chelating N-donor ligands is a proven strategy for the enhancement of the optoelectronic properties of fluorescent dyes. We report dimers based on the boron difluoride hydrazone (BODIHY) framework, which offer unique and sometimes unexpected substituent-dependent absorption, emission, and electrochemical properties. BODIHY dimers have low-energy absorption bands (λ_max=421 to 479 nm, ϵ=17 200 to 39 900 m ⁻¹ cm⁻¹) that are red-shifted relative to monomeric analogues. THF solutions of these dimers exhibit aggregation-induced emission upon addition of water, with emission enhancement factors ranging from 5 to 18. Thin films of BODIHY dimers are weakly emissive as a result of the inner-filter effect, attributed to intermolecular π-type interactions. BODIHY dimers are redox-active and display two one-electron oxidation and two one-electron reduction waves that strongly depend on the N-aryl substituents. These properties are rationalized using density-functional theory calculations and X-ray crystallography experiments.     

第一性原理方法预测水相核酸碱基及其代谢物的氧化还原电动势

氧化还原电动势是了解核酸中电荷/电子转移过程以及设计具有新型氧化还原活性的碱基类化合物的重要参数. 本文对82个芳香化合物的氧化还原电动势进行理论预测, 通过计算值和实验值的比较发现: 气相采用B3LYP/6-311++G(2df,2p)//B3LYP/6-31+G(d)方法, 液相采用HF-COSMORS/UAHF方法, 对运用HF- CPCM/UAHF方法在水相重新优化的构型计算溶剂化能, 能有效预测芳香化合物水相氧化还原电动势, 该理论方法计算的绝对均方根误差(RMSD)为0.124 V. 运用该理论方法成功预测了属于芳香化合物的核酸碱基及其代谢物的水相氧化还原电动势. 根据预测结果, 讨论了核酸中电荷/电子转移过程以及结构改变对设计具有新型氧化还原活性的核酸碱基类化合物的影响. 本文为设计具有氧化还原活性的新型核酸碱基类化合物提供了一种理论方法.     

Reaction center in the oxidation of amino derivatives of 2-phenylbenzimidazole in dimethylformamide

The electrochemical oxidation of amino derivatives of 2-phenylbenzimidazole on a rotating platinum disk with a ring in neutral and acidic dimethylformamide was investigated. It is shown that the investigated compounds are oxidized in two electrochemical steps that include reversible one-electron processes, as a consequence of which the potentials have thermodynamic significance and can serve as a measure of the relative reactivities of these compounds in the oxidation reaction. The imidazole ring undergoes oxidation in acidic media (HClO₄) because of protonation of the amino groups, whereas the amino group is the reaction center in neutral DMF.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 516–518, April, 1978.     

In the presence of very fast comproportionation, sampled current voltammetry and rotating disk electrode voltammetry yield equal two versus one-electron limiting current ratios. Reconciliation through analysis of concentration profiles

A species having three sequential redox states is able to react with its higher oxidation (or lower reduction) state producing two equivalents of its middle redox state. A possible electrochemical signature of that comproportionation reaction is that the faradaic current from the two-electron process (I_1,1) might not be twice the current of the corresponding one-electron process (I_1,2). In this paper, using redox-active species with well-separated one- and two-electron processes, such as N,N′-di-n-heptylviologen, N-methyl-4-benzoylpyridinium perchlorate, TCNQ, TTF, N,N′-dimethylphenazine and TMPD, it is reported that within a wide range of the experimental parameters, two seemingly different electrochemical methods, namely sampled current voltammetry (SCV), a diffusion-controlled method, and rotating disk electrode (RDE) voltammetry, a convection-dominated method, give equal mass-transfer limited current ratios (I_1,2/I_1,1). These phenomena have been traced to the fact that close to the electrode distance-normalized concentration profiles generated from both SCV and RDE voltammetry are superimposable. Digital simulations have confirmed these conclusions, and have led to the elucidation of the relative roles of the comproportionation reaction rate constant, k_f, and the diffusion-layer thickness, δ, in determining the value of the (I_1,2/I_1.1)_{SCV or RDE} ratio: when the diffusion-layer is thicker, the comproportionation reaction time is longer and limiting (I_1,2/I_1,1) ratios are reached with lower k_f values. (The larger δ corresponds to longer sampling times in SCV and slower electrode rotation rates in RDE voltammetry.). Ultimately, the limiting values of the (I_1,2/I_1,1)_{SCV or RDE} ratios are controlled by the relative values of the diffusion coefficients of all three species involved in the comproportionation reaction. According to our results, the (I_1,2/I_1,1)_{SCV or RDE} ratio can afford kinetic information on the comproportionation reaction, and comprises a diagnostic criterion for the relative diffusion coefficients of a redox-active species and its one-electron oxidized (or reduced) form.     

The extended Koopmans' theorem Fock operator and the generalized overlap amplitude one-electron operator

The wave function of a system may be expanded in terms of eigenfunctions of the N −1 electron Hamiltonian times one-particle functions known as generalized overlap amplitudes (GOAS). The one-electron operator whose eigenfunctions are the GOAS is presented, without using an energy-dependent term as in the one-particle Green function or propagator approach. It is shown that this operator and the extended Koopmans' theorem (EKT) one-electron operator are of similar form, but perform complementary roles. The GOA operator begins with one-electron densities and total energies of N −1 electron states to generate the two-matrix and total energy of an N-electron state. The EKT operator begins with the two-matrix of an N-electron state to generate one-electron densities and ionization potentials (or approximations thereto) for N −1 electron states. However, whereas the EKT orbitals must be linearly independent, no such restriction applies to the GOAS. © 1996 John Wiley & Sons, Inc.     

Switching from Metal- to Ligand-Based Oxidation in Cobalt Complexes with Redox-Active Bisguanidine Ligands

The control of the redox reactivity, magnetic and optical properties of the different redox states of complexes with redox-active ligands permits their rational use in catalysis and materials science. The redox-chemistry of octahedrally coordinated high-spin Co^II complexes (three unpaired electrons) with one redox-active bisguanidine ligand and two acetylacetonato (acac) co-ligands is completely changed by replacing the acac by hexafluoro-acetylacetonato (hfacac) co-ligands. The first one-electron oxidation is metal-centered in the case of the complexes with acac co-ligands, giving diamagnetic Co^III complexes. By contrast, in the case of the less Lewis-basic hfacac co-ligands, the first one-electron oxidation becomes ligand-centered, leading to high-spin Co^II complexes with a radical monocationic guanidine ligand unit (four unpaired electrons). Ferromagnetic coupling between the spins on the metal and the organic radical in solution is evidenced by temperature-dependent paramagnetic NMR studies, allowing to estimate the isotropic exchange coupling constant in solution. Second one-electron oxidation leads to high-spin Co^II complexes with dicationic guanidine ligand units (three unpaired electrons) in the presence of hfacac co-ligands, but to low-spin Co^III complexes with radical monocationic, peralkylated guanidine ligand (one unpaired electron) in the presence of acac co-ligands. The analysis of the electronic structures is complemented by quantum-chemical calculations on the spin density distributions and relative energies of the possible redox isomers.     

Polarogmphic study of azo derivatives of 3-hydroxypyridine

It was established that in most cases azo derivatives of 3-hydroxypyridine are reduced successively in two one-electron steps at more positive potentials than azobenzene on a dropping mercury electrode in anhydrous dimethylformamide (DMF) with a 0.05 N solution of tetraethylammonium perchlorate as the base electrolyte. However, one two-electron wave was observed for some compounds; this is evidently associated with self-protonation owing to the presence of the appropriate substituents. Some 3-hydroxypyridine derivatives exist in DMF in various tautomeric forms, as a result of which additional reduction waves appear. More pronounced reduction with respect to the azo group is observed only for three of the investigated compounds.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1240–1244, September, 1981.     

Influence of Methyl Substituent Position on Redox Properties of Nitroaromatics Related to 2,4,6‐Trinitrotoluene

The environmental remediation of military installation sites is very important due to frequently large presence of carcinogenic derivatives of explosives in the ground and in ground waters. These nitroaromatic explosives and their derivatives are assessed by sensing devices. It is highly important to have insight on the reasons affecting the reduction potentials of these compounds. The redox properties of mono‐, di‐ and tri‐nitroaromatic compounds are studied with cyclic voltammetry at a glassy carbon electrode for comparison. We show that the presence of a methyl group in the aromatic system leads into more negative reduction potentials. The ease of nitro group reduction vary from meta>para>ortho positions relative to a methyl group. The redox properties were also studied at various pH ranging from 2 to 10. Acidic environments facilitated the reduction processes at lower potentials. These findings will have a profound influence upon understanding the processes during reductive decontaminations of the polluted sites as well as for construction of highly sensitive sensors for their determination.     

Conjugated and Non-conjugated Polymers Containing Two-Electron Redox Dihydrophenazines for Lithium-Organic Batteries

Organic p-type cathode materials have recently attracted increasing attention due to their higher redox potentials and rate capabilities in comparison to n-type cathodes. However, most of the p-type cathodes based on one-electron redox still suffer from limited stability and low specific capacity (<150 mAh g⁻¹). Herein, two polymers, conjugated poly(diethyldihydrophenazine vinylene) ( CPP ) and non-conjugated poly(diethyldihydrophenazine ethylidene) ( NCPP ) containing two-electron redox dihydrophenazine, have been developed as p-type cathode materials. It is experimentally and theoretically found that the conjugated linkage among the redox centers in polymer CPP is more favorable for the effective charge delocalization on the conjugated polymer backbone and the sufficient oxidation in the higher potential region (3.3–4.2 V vs. Li/Li⁺). Consequently, the CPP cathode displays a higher reversible specific capacity of 184 mAh g⁻¹ with excellent cycling stability.     

N‐methylpicolinium derivatives as the coinitiators in photoinitiating systems for vinyl monomers polymerization

Five N‐methylpicolinium derivatives were investigated to test their abilities to function as second coinitiators in free radical photopolymerization initiated by N,N′‐diethylcarbocyanine—n‐butyltriphenylborate photoredox pair ( P19B2 ). As it is shown by the kinetic data, an addition of picolinium derivatives into P19B2 photoinitiating system visibly increases the efficiency of photoinitiation. The results suggest that the rates of photoinitiation depend on the rate of the picolyl radicals formation. The redox potentials of tested N‐methylpicolinium derivatives were measured and the calculation of free energy change for the possible electron transfer reactions between all components of the system (both stable and transient individuals) was performed. The results suggest that cyanine dyes are able to start a specific chain of an electron transfer reactions involving different coinitiators (borate salt and N‐alkylpicolinium derivatives), giving as a result one photon—two‐radicals photochemical response. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 576–588, 2009     

Macrocycles,derivatives of nitrogen-containing heterocycles 2. Synthesis and electrochemical properties of diindolizinadiquinoxalinacyclooxaalkaphanes

Phenylindolizinylquinoxalinomonopodands, obtained by the reaction of 1-(phenylindolizin-2-yl)quinoxalin-2(1H)-one with corresponding dibromotrioxa- and dibromopentaoxaalkanes, undergo oxidative dehydrocyclization assisted by molecular iodine to yield new redox-active diindolizinadiquinoxalinacyclooxaalkaphanes. Using CVA, the indolizine fragments of the heterocyclophanes in acetonitrile are found to undergo three-step oxidation with transfer of one electron in each step. The first and the third steps are reversible, whereas the second is irreversible. The oxidation at potentials of the first peak leads to the stable radical cations registered by ESR (g = 2.0024, a _2N = 0.26 mT).     

Novel polyviologens: Photochromic redox polymers with film-forming properties

Several novel polyamides containing the N,N′-dialkyl-4,4′-dipyridinium (“viologen”) system were made by interfacial condensation of N,N′-bis(aminoalkyl)-4,4,-dipyridinium salts with di-, tri-, or tetrafunctional acid chlorides. These materials are useful redox polymers which turn deeply colored when reduced chemically or electrically, or when exposed to light.