Homogeneous Electron Transfer Research Articles

Limited Stability of 6,13-Bis(tri(isopropyl)silylethynyl)pentacene upon One-Electron Oxidation: Electrochemically Induced (4 + 2) Cycloaddition between an Alkynyl-Substituted Acene and Its Radical Cation.

6,13-Bis(tri(isopropyl)silylethynyl)pentacene, a particularly stable acene derivative important for (opto)electronic materials, turns reactive upon electrochemical one-electron oxidation. One of the typically stabilizing tri(isopropyl)silylethynyl substituents becomes involved in a (4 + 2) cycloaddition after redox umpolung. The electrosynthetic dimerization of the title compound provides easy access under mild conditions to a complex scaffold, which includes an intact pentacene, an anthracene, and a phenylene unit, all electronically separated. The product's electrochemical redox properties are explained by superimposed cyclic voltammetric features of the pentacene and the anthracene moieties. The reaction path is analyzed on the basis of electroanalytical and ESR data, and an oxidation-cycloaddition-reduction sequence is elaborated. The contribution of homogeneous electron transfers (electron transfer chain reaction) is negligible, in accordance with the relative formal redox potentials of the starting compound and the product. Quantum chemical calculations indicate that the central cycloaddition should be described as a two-step process with a distonic radical cation intermediate. We suggest an extended notation to define the contribution of the components with respect to electron count in the two-step cycloaddition, [3 + 1, 1 + 1].

Spatio-temporal detachment of homogeneous electron transfer in controlling selectivity in mediated organic electrosynthesis.

In electrosynthesis, electron transfer (ET) mediators are normally chosen such that they are more easily reduced (or oxidised) than the substrate for cathodic (or anodic) processes; setting the electrode potential to the mediator therefore ensures selective heterogeneous ET with the mediator at the electrode, rather than the substrate. The current work investigates the opposite, and counter intuitive, situation for a successful mediated electroreductive process where the mediator (phenanthrene) has a reduction potential that is negative to that of the substrate, and the cathode potential is set negative to both (Eele < EM < Es). Simulations reveal a complex interplay between mass transport, the relative concentrations of the mediator and substrate as well as the heterogeneous and homogeneous rate constants for multiple steps, which under suitable conditions, leads to separation of the homogeneous chemistry in a reaction layer detached from the electrode. Reaction layer detachment is a spatio-temporal effect arising due to opposing fluxes of the mediator radical anion M˙- and the substrate 1, which ultimately prevents 1 from reaching the electrode, thereby affording a different reaction pathway. Simulations representative of unstirred batch (1D) and flow (2D) electrolysis are presented, which qualitatively reproduce the experimental selectivity outcomes for mediated and unmediated electroreductive cyclisation of aryl iodide 1. The potential to use highly reducing homogeneous ET agents, possessing reduction potentials beyond those of the substrates, offers exciting opportunities in mediated electrosynthesis.

Homogeneous interfacial electron transfer promotes photoinduced hole extraction for phenol mineralization

We here developed a fixed-bed photocatalyst based on homogeneous contact that can synergistically promote the generation of hydroxyl radicals by facilitating semiconductor–cocatalyst-solution interfacial electron transfer.

Electrosynthesis of Au nanocluster embedded conductive polymer films at soft interfaces using dithiafulvenyl-functionalized pyrene.

Nanoparticle (NP) embedded conductive polymer films are desirable platforms for electrocatalysis as well as biomedical and analytical applications. Increased catalytic and analytical performance is accompanied by concomitant decreases in NP size. Herein, highly reproducible electrogeneration of low dispersity Au nanocluster embedded ultra-thin (∼2 nm) conductive polymer films at a micro liquid|liquid interface is demonstrated. Confinement at a micropipette tip facilitates a heterogeneous electron transfer process across the interface between two immiscible electrolyte solutions (ITIES), between KAuCl4(aq) and a dithiafulvenyl-substituted pyrene monomer, 4,5-didecoxy-1,8-bis(dithiafulven-6-yl)pyrene (bis(DTF)pyrene), in oil, i.e., a w|o interface. At a large ITIES the reaction is spontaneous, rapid, and proceeds via transfer of AuCl4- to the oil phase, followed by homogeneous electron transfer generating uncontrolled polymer growth with larger (∼50 nm) Au nanoparticles (NPs). Thus, miniaturization facilitates external, potential control and limits the reaction pathway. Atomic (AFM) and Kelvin probe force microscopies (KPFM) imaged the topography and work function distribution of the as-prepared films. The latter was linked to nanocluster distribution.

Cathodic Radical Cyclisation of Aryl Halides Using a Strongly-Reducing Catalytic Mediator in Flow.

Electro‐reductive radical cyclisation of aryl halides affords the corresponding hetero‐ and carbo‐cycles in an undivided flow reactor equipped with steel and carbon electrodes using an organic mediator. A dissolving metal anode is not needed, and the mediator can be employed in a sub‐stoichiometric amount (0.05 equiv), increasing the practical utility of cathodic radical cyclisation. The methodology is applied to O‐, N‐, and C‐tethers, yielding tricyclic fused and spiro systems. In the absence of mediator, the major pathway is hydrogenolysis of the C−X bond, a 2 e− process occurring at the cathode. Predominance of the radical pathway in presence of a strongly reducing mediator (M) is consistent with homogeneous electron‐transfer in a reaction layer detached from the cathode surface, where the flux of M .− leaving the electrode is such that little aryl halide reaches the cathode.

Tailored interface stabilization of FTO transparent conducting electrodes boosting electron and Li ion transport for electrochromic energy-storage devices

• Highly smooth morphology and oxygen vacancy passivated structure of W-FTO/H 2 O 2 films. • Dense and smooth surface of W-FTO/H 2 O 2 provide homogeneous electron transport. • Oxygen vacancy passivation structure of W-FTO/H 2 O 2 provides fast electron transport. • Tailored interface stabilization of WO 3 //FTO electrodes for EC energy-storage devices. Transparent conducting electrodes (TCEs) play an important role in transporting electrons to an active layer, which directly affects electrochemical reactions in electrochromic (EC) energy-storage devices. However, homogeneous and fast electron supply to electrochemically active layer is mainly limited by interfacial properties of the TCE. Especially, a rough interfacial structure leads to redundant voids for electron scattering, and an oxygen vacancy acts as an intrinsic electron-trapping site in TCE. Thus, we propose a highly smooth morphology and oxygen vacancy passivated TCE to boost electron and Li ion transport without an active material (WO 3 ) adjustment. These nanostructures are synthesized with simultaneous effects of W co-doping and H 2 O 2 during spray pyrolysis deposition (W-FTO/H 2 O 2 ) for application in EC energy-storage devices. The highly dense and smooth surface of W-FTO/H 2 O 2 provides a homogeneous electron supply to WO 3 , which induces uniform Li ion transport into WO 3 . And the oxygen vacancy passivated structure encourages electron mobility, which leads to in-depth Li ion transport. Consequently, the EC energy-storage electrodes fabricated with W-FTO/H 2 O 2 as a TCE exhibited ultra-fast switching speeds (2.3 s for coloration and 0.6 s for bleaching) and a high rate capability because of the high electron mobility. An all-solid-state cell fabricated with W-FTO/H 2 O 2 as a TCE exhibited remarkable cyclic stability (transmittance retention of 92% and specific capacitance retention of 95.8% after 2,000 continuous cycles) because of the homogeneous electron transfer at the interface. Therefore, we demonstrate that tailoring interface structure of TCE is a promising strategy to improve the performance of EC energy-storage devices.

The role of molecular interaction between GOD and metal complexes on redox mediation processes

In this work, we study the redox mediation of glucose oxidase (GOD) with a series of Co(II) polypyridine complexes [CoIIL3]2+ (L = 5-Nitro-1,10-phenanthroline, 5-Chloro-1,10-phenanthroline, 5-Bromo-1,10-phenanthroline, 1,10-phenanthroline and 5-methyl-1,10-phenanthroline) and Ferrocenecarboxylic acid (Fc-COOH), in order to understand the role of molecular interaction GOD-mediator on homogeneous electron transfer rate constant (ks), exploring Marcus cross-relation and tunneling effect model, not reported before. The ks values were calculated through a foot of the wave analysis (FOWA) from cyclic voltammetry data. Circular Dichroism spectroscopy reveals no structural changes in the enzyme in the presence of the redox mediators. The interaction energy between GOD and Co(II) complexes and a series of ferrocene derivatives (FcCOOH, Fc-CH2NH(CH3)2, Fc-1,1-CH3, Fc-CHCH2, and Fc) was calculated using DFT and molecular docking. Quantitative Structure-Activity Relationship (QSAR) analyses were explored to rationalize ks values with theoretical calculations. The results allow us to propose that the GOD-mediator interaction, should be considered for a better description of the electron transfer process, useful for potential bioelectronic applications.

Defect {(WVIO7)WVI4} and Full {(WVIO7)WVI5} Pentagonal Units as Synthons for the Generation of Nanosized Main Group V Heteropolyoxotungstates.

We report on the synthesis and characterization of three new nanosized main group V heteropolyoxotungstates KxNay[H2(XWVI9O33)(WVI5O12)(X2WVI29O103)]·nH2O {X3W43} (x = 11, y = 16, and n = 115.5 for X = SbIII; x = 20, y = 7, and n = 68 for X = BiIII) and K8Na15[H16(CoII(H2O)2)0.9(CoII(H2O)3)2(WVI3.1O14)(SbIIIWVI9O33)(SbIII2WVI30O106)(H2O)]·53H2O {Co3Sb3W42}. On the basis of the key parameters for the one-pot synthesis strategy of {Bi3W43}, a rational step-by-step approach was developed using the known Krebs-type polyoxotungstate (POT) K12[SbV2WVI22O74(OH)2]·27H2O {Sb2W22} as a nonlacunary precursor leading to the synthesis and characterization of {Sb3W43} and {Co3Sb3W42}. Solid-state characterization of the three new representatives {Bi3W43}, {Sb3W43}, and {Co3Sb3W42} by single-crystal and powder X-ray diffraction (XRD), IR spectroscopy, thermogravimetric analysis (TGA), energy-dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), and elemental analysis, along with characterization in solution by UV/vis spectroscopy shows that {Bi3W43}, {Sb3W43}, and {Co3Sb3W42} represent the first main group V heteropolyoxotungstates encapsulating a defect {(WVIO7)WVI4} ({X3W43}, X = BiIII and SbIII) or full {(WVIO7)WVI5} ({Co3Sb3W42}) pentagonal unit. With 43 tungsten metal centers, {X3W43} (X = BiIII and SbIII) are the largest unsubstituted tungstoantimonate– and bismuthate clusters reported to date. By using time-dependent UV/vis spectroscopy, the isostructural representatives {Sb3W43} and {Bi3W43} were subjected to a comprehensive study on their catalytic properties as homogeneous electron-transfer catalysts for the reduction of K3[FeIII(CN)6] as a model substrate revealing up to 5.8 times higher substrate conversions in the first 240 min (35% for {Sb3W43}, 29% for {Bi3W43}) as compared to the uncatalyzed reaction (<6% without catalyst after 240 min) under otherwise identical conditions.

Homogeneous molecular catalysis of the electrochemical reduction of N2O to N2: redox vs. chemical catalysis.

Homogeneous electrochemical catalysis of N2O reduction to N2 is investigated with a series of organic catalysts and rhenium and manganese bipyridyl carbonyl complexes. An activation-driving force correlation is revealed with the organic species characteristic of a redox catalysis involving an outer-sphere electron transfer from the radical anions or dianions of the reduced catalyst to N2O. Taking into account the previously estimated reorganization energy required to form the N2O radical anions leads to an estimation of the N2O/N2O˙− standard potential in acetonitrile electrolyte. The direct reduction of N2O at a glassy carbon electrode follows the same quadratic activation driving force relationship. Our analysis reveals that the catalytic effect of the mediators is due to a smaller reorganization energy of the homogeneous electron transfer than that of the heterogeneous one. The physical effect of “spreading” electrons in the electrolyte is shown to be unfavorable for the homogeneous reduction. Importantly, we show that the reduction of N2O by low valent rhenium and manganese bipyridyl carbonyl complexes is of a chemical nature, with an initial one-electron reduction process associated with a chemical reaction more efficient than the simple outer-sphere electron transfer process. This points to an inner-sphere mechanism possibly involving partial charge transfer from the low valent metal to the binding N2O and emphasizes the differences between chemical and redox catalytic processes.

Homogeneous electron-transfer reaction between anionic species of anthraquinone derivatives and molecular oxygen in acetonitrile solutions: Electrochemical properties of disperse red 60

In this work, the voltammetric behaviour of disperse red 60 (DR60) in acetonitrile solutions in the presence of water and dioxygen (O2) is reported for the first time. DR60 can be reduced in two one-electron steps to form first the anion radical and then the dianion. The first reduction process of DR60 is affected by the water content of the acetonitrile, with digital simulations of the cyclic voltammetric waves supporting interactions between the radical anion and water molecules. Additionally, the presence of O2 modifies the first voltammetric process of DR60, suggesting the occurrence of homogeneous electron transfer reaction between anion radicals of DR60 and O2. Furthermore, the water content of the acetonitrile also affects the reduction wave of O2, with digital simulations supporting the occurrence of two association steps with the superoxide intermediate. The homogeneous electron transfer reaction between the quinone and oxygen species was also examined by reacting bulk electrolyzed solutions containing the anions of DR60 and O2 with neutral species of O2 and DR60, respectively, and recording the variation in the colour of the electrolyzed solutions. An equilibrium constant value was obtained from the difference between the formal reduction potentials of DR60 and O2 (−0.9955 and −0.9770, respectively, both vs. Ag in CH3CN with 0.5 M n-Bu4NPF6), indicating the direction of the homogenous electron transfer reaction (Keq = 2.013). Similarly, to confirm the occurrence of the homogeneous electron transfer reaction between O2 and another quinone based molecule, cyclic voltammetry and bulk electrolysis experiments were carried out on 9,10-anthraquinone (AQ), and its equilibrium constant value was also obtained (Keq = 4.392).

Photochemical Properties of Re(CO)3 Complexes with and without a Local Proton Source and Implications for CO2 Reduction Catalysis

Herein, we present a detailed study on the photophysical properties and the excited state reactivity of two mononuclear Re(CO)3 complexes with imdazol-pyridine ligands equipped with and without a local proton source, [Re(CO)3LCl], where for 1: L = 2,4-ditert-butyl-6-(6-(1-methyl-1H-imidazol-2-yl)pyridin-2-yl)phenol and 2: L = 2-(3,5-ditert-butyl-2-methoxyphenyl)-6-(1-methyl-1H-imidazol-2-yl)pyridine. Time-resolved IR and UV/vis spectroscopy revealed that excitation of 1 and 2 is followed by population of the triplet excited state within <100 fs, where structural and vibrational relaxation to the T1 equilibrium structure is observed on the picosecond time scale. The T1 state can be viewed as a MLCT state as all ν(CO) features in the transient infrared (TRIR) spectra are shifted to higher wavenumbers upon excitation, which is indicative for a decreasing Re → CO π-backdonation. The T1 states have considerably long lifetimes at room temperature of 160 ns for 1 and 430 ns for 2 in dmf and they can be successfully quenched by the sacrificial electron donors triethanolamine (TEOA) and 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH). The quenching rates are 2 orders of magnitude larger for BIH than for TEOA, as the latter reaction is endergonic. However, both species are not active in the photochemical CO2-to-CO conversion. We rationalize this for 2 by the low steady-state concentration of the initial reduction product, [Re(CO)3LCl]−, which ejects chloride rather fast. Thus, the second, homogeneous electron transfer process between [Re(CO)3LCl]− and [Re(CO)3L(solvent)] forming the active species [Re(CO)3L]−, has a very low probability and decomposition pathways come to the fore. 1 decomposes under irradiation in the presence of BIH or TEOA forming the initial photoproduct 3. We tentatively assume that the ligand in 3 is deprotonated and switches from a N,N- to a N,O–-coordination mode. This indicates that in the excited state the Re–N bond is cleaved quite easily, as this decomposition pathway has not been observed under electrochemical conditions.

An investigation of homogeneous electrocatalytic mechanism between ferrocene derivatives and l-cysteine/N-Acetyl-l-cysteine

The homogeneous electrocatalytic mechanism with a fast catalytic chemical reaction between a series of ferrocene derivatives and l-cysteine/N-Acetyl-l-cysteine (NAC) is systematically investigated. A comparison of different cyclic voltammetric waveforms is given to illustrate the interaction between kinetic parameter (λ) and excess factor (γ) in kinetic zone diagram via changing the scan rates and substrate/mediator ratio on both glassy carbon (GC) and boron doped diamond (BDD) working electrode experimentally. A split wave phenomenon is observed between ferroceneacetic acid (FAA) and l-cysteine. Also, the waveforms revealed that electron withdrawing groups (EWG) on the substrate hinders the kinetics of the homogeneous electron transfer while those on the mediator facilitates the same process. The homogeneous electrocatalytic order of the studied mediator is as follows: 1,1′-ferrocenedicarboxylic acid (FDA) > FAA > hydroxymethylferrocene (HMF) > 1-hydroxyethylferrocene (HEF) and the corresponding density functional theory (DFT) calculation is applied to support this statement. Furthermore, the second-order rate constant between FAA and l-cysteine is given by the support of numerical simulation (175 (mol m−3)−1 s−1). The present study would facilitate the understanding of homogeneous electrocatalytic process, especially those possessing a fast catalytic chemical step.

Homogeneous electron-transfer of chlorophyll and its derivative chlorophyllin at gold electrode

Introduction: Chlorophyll is a light harvesting pigment, which absorbs light in the visible spectrum of sunlight and promotes electron transfer, Chlorophyllin (CHL) is One of the most important derivative molecules of chlorophyll. Nowadays, chlorophyll pigment and its derivatives are utilised in organic photosynthetic solar cells for their desirable photovoltaic properties. Cyclic voltammetry (CV) is an essential technique. It is extensively used to study electroactive species to interpret the intermediates of reactions, supply information about the thermodynamics of oxidation-reduction reactions and elucidate the kinetics of electron transfer reactions. Materials and Methods: Prior to the electrochemical study, the working gold (Au) electrode surface was prepared by immersing it in the various concentrations of chlorophyllin for a period time. The electrolyte was degassed by using N2 for approximately 30 minutes inside a Faraday cage before any electrochemical experiment was performed. A three electrode system was used with, Ag/AgCl as a reference electrode, graphiteas a counter and the working electrode (Au). Results and Discussion: As a route to develop new chemical systems for artificial photosynthesis, this work reports the effectiveness of different parameters in transferring electrons between chlorophyllin (CHL) pigment and the working electrode surface (gold). These parameters such as the adsorption time, the electrolyte nature and concentration and chlorophyllin concentration are investigated. The use of chlorophyllin as a redox mediator is examined, with a gold electrode being employed. The importance of gold electrode surface preparation in determining the mechanism of redox is described, and the environment of adsorption process of the different concentrations of chlorophyllin on the surface of the gold electrode has been elucidated in this study. Conclusiones: The electrochemical method showed that the cyclic voltammetry responses of studied adsorption chlorophyllin pigment on the gold electrode were more efficient. In addition, the redox reaction was successful electrochemically in aqueous solution thanthe organic solution. It was suggested that electrons reduce to the chlorophyllin pigment by adding active species in the bulk solution homogeneous transfer. Finally, detections of chl on spinach leaves using various methods are reported.

Revisiting the role of π acceptor character of polypyridinc ligands in the redox behavior of tris and bis Fe(II) complexes and in the electron transfer with glucose oxidase

In this work we revisit the role of π-acceptor character of polypyridinc ligands in the electrochemical behavior of bis and tris Fe(II) complexes [FeL3]2+ and [FeL′2]2+ and in the electron transfer with a representative redox enzyme, glucose oxidase GOD; (L = 1,10-phen, 5-chloro-1,10-phen, 5-nitro-1,10-phen, 5-methyl-1,10-phen, 4-methyl-1,10-phen, 5,6-dimethyl-1,10-phen, 4,7-dimethyl-1,10-phen, 2,2′-bipy, 5,5′-dimethyl-2,2′-bipy, 4,4′-dimethyl-2,2′-bipy, L′ = 2,2′6′,6″-terpy and 4-chloro-2,2′:6′,6″-terpy). The compounds presented a reversible electron transfer [Fe(II)Ln]2+ → [Fe(III)Ln]3+ 1e, (n = 1,2) followed by an unexpected coupled chemical reaction, ECi mechanism. It was established that the redox potential (E°) and the rate constant (kf) of couple reaction are tuned by the pKa of non-coordinated ligand (π acceptor character descriptor). Using UV–vis spectroelectrochemistry different products are proposed for the ECi mechanism. DFT calculations, allow us to state that changes in E°, and pKa are related to HOMO energies. Linear relationships among the electrochemical and kinetic values E°, kf, with the pKa of the ligands were obtained. Using Foot of the Wave Analysis (FOWA) the homogenous electron transfer rate constant (ks) for GOD mediation was calculated. From data obtained in this work and choosing similar complexes from literature, it was explored the role of redox potential in this redox mediation.

Thiolated DAB Dendrimers-Gold Nanoparticles as Self-Assembled Layers for the Direct Electrochemistry of HRP

In this work, three generations of a thiolated DAB dendrimer have been used as bonding-layer between electrodeposited and colloidal gold nanoparticles of several sizes to develop electrocatalytic self-assembled layers for the covalent immobilization and direct electrochemistry of horseradish peroxidase (HRP). This study covers the kinetic, electrochemical and analytical characterization of all the prepared biosensors with the aim of developing the best electrocatalytic basis for future oxidase-peroxidase bienzymatic biosensors or biosensors based on the HRP inhibition. The best results were obtained with the dendrimer of third generation and 16 nm colloidal gold nanoparticles, which showed a homogeneous electron transfer rate constant of 422 s−1. This self-assembled monolayer was the most efficient to contact with the HRP active centre and allowed to determine hydrogen peroxide at an applied potential −0.3 V in three linear ranges of 0.4-200; 200–700 and 700–4000 μM with high sensitivities of 590; 441 and 303 μA mM−1 cm−2 respectively, low detection limit of 20 nM and fast response. The obtained apparent overall rate and Michaelis-Menten constants for this optimal biosensor were 0.047 A M−1 and 1.16 mM respectively. This last one, is significantly lower than the intrinsic K'M revealing the very high enzymatic efficiency of the developed devices.

Medicinal Electrochemistry of Halogenated and Nitrated Pterocarpanquinones

Electrochemical methods are considered useful tools for simulations of biological redox reactions. The activities of quinones depend on their bioreduction. Biologically active pterocarpanquinones LQB-149 (nitroderivative), 150 and 151 (bromo and chloroderivatives, respectively) were electrochemically investigated by cyclic voltammetry, differential pulse voltammetry, and in situ UV-Vis spectroelectrochemistry, in aprotic media (N,N-dimethylformamide (DMF) + tetra-N-butylammonium (TBAPF6)). The data obtained regarding their reduction mechanisms, positive reactivity with oxygen and analysis of the electrogenerated intermediates were useful in explaining their biological outcomes. The appearance of bands at 397 and 480 nm, for the halogenated compounds, suggests the generation of transient quinonemethides (QM), electrophilic intermediates related to their activity. As an additional proof for the intermediacy of QM, in the redox processes, chemical reduction of LQB-150, in the presence of hexanethiol was performed and led to a thioalkylated quinone. For the nitroderivative, a broad band appeared at 432 nm, corresponding to the generation of the nitroradical anion, giving rise to a dianion diradical, after reduction at the second wave potential. Computational data correlate well with electrochemical experiments. Homogeneous electron transfer to oxygen, yielding reactive oxygen species, the generation of electrophilic species and the radical reactivity, explain partially the mechanism of biological action.

Efficient homogeneous and isomorphic blocking layer – Skeleton rutile TiO2 electron transfer structure for quantum dot sensitized solar cells

Abstract Blocking layer and transfer skeleton of the electron transfer layer are found to play a crucial role in devices efficiency improvement. We develop a homogeneous and isomorphic electron transfer structure of rutile TiO2 by preferred orientation growth in a facile two-step hydrothermal synthesis. The aligned TiO2 nanowire array skeleton (TS) about 2.47 μm long grew neatly over the isomorphic ultra-thin blocking layer (BL). Those homogeneous and isomorphic structures promote the charge injection and transfer capability by means of increased driving force by higher Fermi-level and decreased resistance, in which the cell photocurrent and PCE improve significantly. Of the cells with isomorphic transfer structure, the PCE is 2.87%, the short-circuit current (Jsc) is 6.74 mA/cm2, open-circuit voltage (Voc) is 0.91 V and fill factor (FF) is 38.4% under one sun illumination (100 mW/cm2).

Synthesis and NMR characterization of a spirosilole tetra-anion: a homogeneous four-electron reductant

Abstract The development of highly selective homogeneous electron transfer reagents is highly desirable for synthetic chemistry. An isolable spirosilole tetra-anion described in this paper has been proved to be a promising soluble electron transfer reagent. The reduction of octaphenyl-1,1′-spirobisilole (1) with lithium resulted in the formation of the isolable spirosilole tetra-anion in good yield. The tetra-anion (2) has been characterized by nuclear magnetic resonance (NMR) and cleanly underwent electron transfer reactions with dioxygen, carbonyl groups, and transition metal halides to yield reduction products with the regeneration of 1.

Synthesis of K2Se solar cell dopant in liquid NH3 by solvated electron transfer to elemental selenium

This study explores the rich chemistry of elemental selenium reduction to monoselenide anions. The simplest possible homogeneous electron transfer occurs with free electrons, which is only possible in plasmas; however, alkali metals in liquid ammonia can supply unbound electrons at much lower temperatures, allowing in situ analysis. Here, solvated electrons reduce elemental selenium to K2Se, a compound relevant for alkali metal doping of Cu(In,Ga)Se2 solar cell material. It is proposed that the reaction follows pseudo first-order kinetics with an inner-sphere or outer-sphere oxidation semi reaction mechanism depending on the concentration of solvated electrons.

Behavior of Ionic Liquids Around Charged Metal Complexes: Investigation of Homogeneous Electron Transfer Reactions Between Metal Complexes in Ionic Liquids

The second-order electron transfer reaction between the photo-excited triplet state of [Zn(TPP)]* (TPP = 5,10,15,20-tetraphenylporphyrin) and [Co(sep)]3+ (sep = sepulchrate = 1,3,6,8,10,13,16,19-octaazabicyclo[6.6.6]eicosane) was investigated in three ionic liquids (ILs, 1-R-3-methylimidazolium bis(trifluoromethylsulfonyl)imide with R = butyl, pentyl, and hexyl) and in acetonitrile. Results of electrochemical and kinetic measurements indicated that ILs dissociate in the vicinity of charged metal complexes and at electrodes, although the dissociated anionic and cationic components of the ILs seem to exist as pairs around the metal complexes. Second-order rate constants for the electron transfer reaction are 1.88 × 109, 3.65 × 107, 2.63 × 107, and 2.01 × 107 kg·mol−1·s−1 in acetonitrile and in the butyl, pentyl and hexyl ILs, respectively, at 298 K, after correction of the contribution of diffusion. The average slope of the plot of the logarithmic second-order rate constants observed in acetonitrile and ILs against the logarithmic viscosity of each solvent was − 0.84. However, the slope of the same plot was much steeper (− 4.1) when data for only the three ILs were used. Detailed analyses of the experimental results on the basis of the Latner–Levin cross relation and the Marcus theory lead to the conclusion that the solvent properties such as the dielectric constant and refractive index around the polarized/charged transition states are different from those for the bulk ILs: observed self-exchange rate constants did not exhibit the Pekar factor dependence when dielectric constants and refractive indices for bulk ILs are used.