Cyclic Voltammetric Analysis of Ferrocene Alkanethiol Monolayer Electrode Kinetics Based on Marcus Theory

Designing Benzodithiophene-Based Small Molecule Donors for Organic Solar Cells by Regulation of Halogenation Effects

The donors are key components of organic solar cells (OSCs) and play crucial roles in their photovoltaic performance. Herein, we designed two new donors (BTR-γ-Cl and BTR-γ-F) by finely optimizing small molecule donors (BTR-Cl and BTR-F) with a high performance. The optoelectronic properties of the four donors and their interfacial properties with the well-known acceptor Y6 were studied by density functional theory and time-dependent density functional theory. Our calculations show that the studied four donors have large hole mobility and strong interactions with Y6, where the BTR-γ-Cl/Y6 has the largest binding energy. Importantly, the proportion of charge transfer (CT) states increases at the BTR-γ-Cl/Y6 (50%) and BTR-γ-F/Y6 (45%) interfaces. The newly designed donors are more likely to achieve CT states through intermolecular electric field (IEF) and hot exciton mechanisms than the parent molecules; meanwhile, donors containing Cl atoms are more inclined to produce CT states through the direct excitation mechanism than those containing F atoms. Our results not only provided two promising donors but also shed light on the halogenation effects on donors in OSCs, which might be important to design efficient photovoltaic materials.

Non-Covalent Interactions Mimic the Covalent: An Electrode-Orthogonal Self-Assembled Layer

Charge-transfer events central to energy conversion and storage and molecular sensing occur at electrified interfaces. Synthetic control over the interface is traditionally accessed through electrode-specific covalent tethering of molecules. Covalent linkages inherently limit the scope and the potential stability window of molecularly tunable electrodes. Here, we report a synthetic strategy that is agnostic to the electrode's surface chemistry to molecularly define electrified interfaces. We append ferrocene redox reporters to amphiphiles, utilizing non-covalent electrostatic and van der Waals interactions to prepare a self-assembled layer stable over a 2.9 V range. The layer's voltammetric response and in situ infrared spectra mimic those reported for analogous covalently bound ferrocene. This design is electrode-orthogonal; layer self-assembly is reversible and independent of the underlying electrode material's surface chemistry. We demonstrate that the design can be utilized across a wide range of electrode material classes (transition metal, carbon, carbon composites) and morphologies (nanostructured, planar). Merging atomically precise organic synthesis of amphiphiles with in situ non-covalent self-assembly at polarized electrodes, our work sets the stage for predictive and non-fouling synthetic control over electrified interfaces.

Incorporation of a Boron-Nitrogen Covalent Bond Improves the Charge-Transport and Charge-Transfer Characteristics of Organoboron Small-Molecule Acceptors for Organic Solar Cells

An organoboron small-molecular acceptor (OSMA) M_B←N containing a boron-nitrogen coordination bond (B←N) exhibits good light absorption in organic solar cells (OSCs). In this work, based on M_B←N, OSMA M_B-N, with the incorporation of a boron-nitrogen covalent bond (B-N), was designed. We have systematically investigated the charge-transport properties and interfacial charge-transfer characteristics of M_B-N, along with M_B←N, using the density functional theory (DFT) and the time-dependent density functional theory (TD-DFT). Theoretical calculations show that M_B-N can simultaneously boost the open-circuit voltage (from 0.78 V to 0.85 V) and the short-circuit current due to its high-lying lowest unoccupied molecular orbital and the reduced energy gap. Moreover, its large dipole shortens stacking and greatly enhances electron mobility by up to 5.91 × 10^-3 cm²·V^-1·s^-1. Notably, the excellent interfacial properties of PTB7-Th/M_B-N, owing to more charge transfer states generated through the direct excitation process and the intermolecular electric field mechanism, are expected to improve OSCs performance. Together with the excellent properties of M_B-N, we demonstrate a new OSMA and develop a new organoboron building block with B-N units. The computations also shed light on the structure-property relationships and provide in-depth theoretical guidance for the application of organoboron photovoltaic materials.

Electrocatalytic Investigation by Improving the Charge Kinetics between Carbon Electrodes and Dopamine Using Bio-Synthesized CuO Nanoparticles

We have successfully studied the charge transfer kinetics between carbon paste electrodes and dopamine using green synthesized rectangular monoclinic CuO nanoparticles (NPs) prepared by Alchemilla vulgaris leaves with the one-pot green synthesis method. The scanning electron microscopy (SEM) results confirmed the monoclinic structure with a particle size of around 85 nm. The investigation of thermal properties was carried out by thermogravimetric (TG) and differential thermal analysis (DTA). We also studied the electrochemical response of green synthesized CuO nanoparticles to detect Dopamine (DA) using cyclic voltammetry, which was proven to be an excellent electrocatalyst for the electro-oxidation of DA. The fabricated CuO nanoparticle modified carbon paste electrode (CMCPE) depicts fantastic selectivity, robustness, and sensitivity in analyzing DA in clinical and pharmaceutical preparations. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) orbitals of the DA were studied using positive and negative charges at the CuO modified carbon paste electrode interface. Frontier molecular orbitals of DA are plotted to understand electron transfer reactivity at the electrode interface.

Photoelectrochemical sandwich immunoassay of CYFRA21-1 based on In2O3/WO3 type-II heterojunction and CdS quantum dots-polydopamine nanospheres labeling

Using an In₂O₃/WO₃ type-II heterojunction modified fluorine-doped tin oxide (FTO) electrode as the photoanode and CdS quantum dots (QDs)-polydopamine nanospheres (PDA NSs) as the secondary antibody (Ab₂) label, the photoelectrochemistry (PEC) sandwich immunosensing of the lung cancer marker CYFRA21-1 was studied. WO₃ nanoplates were prepared by a hydrothermal method, In₂O₃ nanoporous spheres were prepared by a hydrothermal method followed by calcination, and the In₂O₃/WO₃ type-II heterojunction with high PEC activity was prepared by ultrasonic mixing and cast-coating. PDA NSs with a high surface area can be loaded with abundant Ab₂ molecules and many CdS QDs with an energy level well matched with the heterojunction, so the photocurrent signal can be amplified by the formation of a sandwich immunostructure. Through the simulation experiments of photoelectrode-modified chitosan films of varying thickness, the effective transport distance of photogenerated charges is preliminarily discussed. Under the optimized conditions, the photocurrent was linear with the common logarithm of CYFRA21-1 concentration from 100 fg mL^-1 to 50 ng mL^-1, with a limit of detection of 56 fg mL^-1 (S/N = 3). The immunoassay of CYFRA21-1 in human serum samples gave satisfactory recovery results.

Theoretical Study of Non-Fullerene Acceptors Using End-Capped Groups with Different Electron-Withdrawing Abilities toward Efficient Organic Solar Cells

Acceptors in organic solar cells (OSCs) are of paramount importance. On the basis of the well-known non-fullerene acceptor Y6, six acceptors (Y6-COH, Y6-COOH, Y6-CN, Y6-SO₂H, Y6-CF₃, and Y6-NO₂) were designed by end-capped manipulation. The effects of end-capped engineering on electronic properties, optical properties, and interfacial charge-transfer states were systematically studied by density functional theory, time-dependent density functional theory, and molecular dynamics. The designed acceptors possess suitable energy levels and improved optical properties. More importantly, the electron mobility of the new acceptors was greatly enhanced, even more than 20 times that of the parent molecule. Among them, Y6-NO₂ with the lowest-lying frontier molecular orbitals and the largest red-shifted absorption was selected to construct interfaces with the donor PM6. PM6/Y6-NO₂ exhibits stronger interfacial interactions and enhanced charge-transfer characteristics compared with PM6/Y6. This work not only enhances the understanding of the structure-property relationship for acceptors but also offers a set of promising acceptors for high-performance OSCs.

Mechanisms, kinetics and eco-toxicity assessment of singlet oxygen, sulfate and hydroxyl radicals-initiated degradation of fenpiclonil in aquatic environments

Fenpiclonil is an agricultural phenylpyrrole fungicide, which raise the concern about its ecotoxicological effects. In this paper, we investigate the indirect photochemical transformation mechanisms, environmental persistence and eco-toxicity of fenpiclonil initiated by various active oxidants (¹O₂, •OH and SO₄•‾) in aquatic environments. The results shown that ¹O₂ can react with pyrrole ring by cycloaddition pathways to form the endo-peroxides. In addition, •OH and SO₄•‾ initial mechanisms are calculated, suggesting that •OH-initiated mechanisms play a dominant role in the degradation process of fenpiclonil at high rate constants (2.26 ×10⁹ M^-1 s^-1, at 298 K). The kinetic calculation results indicate that high temperature is more favorable for the degradation of fenpiclonil. To better understand the adverse effects of the transformation products formed during the subsequent reaction of •OH-adduct IM10, the computational toxicology has been used for the toxicity estimation. The results show that aquatic toxicity of these products decrease with degradation process, especially the decomposition products (TP3 and TP4). However, TP1 and TP2 are still toxic and developmental toxicant. The study provides guidance for further experimental research and industrial application of fungicide degradation from the perspective of theoretical calculation.

Unravelling electron transfer in peptide-cation complexes: a model for mimicking redox centres in proteins

We provide evidence that bound zinc promotes electron transfer in a peptide by changing the electronic properties of the peptide.

Synthesis of a novel ferrocene-based epoxy compound and its burning rate catalytic property

3-(Ferrocenylcarbonyl)propionic acid diglycidyl ester (FCPADE) was synthesized and characterized. Its electrochemical behavior, catalytic performance on decomposition of AP and anti-migration property were investigated.

Gold nanoparticle-mediated electron transfer of cytochrome c on a self-assembled surface

Gold nanoparticles provide short-range electron transfer between cytochrome c and gold electrode.

Catalysis by electrons and holes: formal potential scales and preparative organic electrochemistry

The present review surveys current chemical understanding of catalysis by addition and removal of an electron.

Distortion–interaction analysis along the reaction pathway to reveal the reactivity of the Alder-ene reaction of enes

The reactivity of uncatalyzed Alder-ene type reactions of hetero-substituted propylene is interpreted by distortion–interaction analysis of both the transition states and the complete reaction pathways.

Long-range electron transfer with myoglobin immobilized at Au/mixed-SAM junctions: mechanistic impact of the strong protein confinement

Horse muscle myoglobin (Mb) was tightly immobilized at Au-deposited ~15-Å-thick mixed-type (1:1) alkanethiol SAMs, HS-(CH₂)₁₁-COOH/HS-(CH₂)₁₁-OH, and placed in contact with buffered H₂O or D₂O solutions. Fast-scan cyclic voltammetry (CV) and a Marcus-equation-based analysis were applied to determine unimolecular standard rate constants and reorganization free energies for electron transfer (ET), under variable-temperature (15-55 °C) and -pressure (0.01-150 MPa) conditions. The CV signal was surprisingly stable and reproducible even after multiple temperature and pressure cycles. The data analysis revealed the following values: standard rate constant, 33 s⁻¹ (25 °C, 0.01 MPa, H₂O); reorganization free energy, 0.5 ± 0.1 eV (throughout); activation enthalpy, 12 ± 3 kJ mol⁻¹; activation volume, -3.1 ± 0.2 cm³ mol⁻¹; and pH-dependent solvent kinetic isotope effect (k(H)⁰/k(D)⁰), 0.7-1.4. Furthermore, the values for the rate constant and reorganization free energy are very similar to those previously found for cytochrome c electrostatically immobilized at the monocomponent Au/HS-(CH₂)₁₁-COOH junction. In vivo, Mb apparently forms a natural electrostatic complex with cytochrome b₅ (cyt-b₅) through the "dynamic" (loose) docking pattern, allowing for a slow ET that is intrinsically coupled to the water's removal from the "defective" heme iron (altogether shaping the biological repair mechanism for Mb's "met" form). In contrary, our experiments rather mimic the case of a "simple" (tight) docking of the redesigned (mutant) Mb with cyt-b₅ (Nocek et al. J. Am. Chem. Soc. 2010, 132, 6165-6175). According to our analysis, in this configuration, Mb's distal pocket (linked to the "ligand channel") seems to be arrested within the restricted configuration, allowing the rate-determining reversible ET process to be coupled only to the inner-sphere reorganization (minimal elongation/shortening of an Fe-OH₂ bond) rather than the pronounced detachment (rebinding) of water and, hence, to be much faster.

Evidence of short-range electron transfer of a redox enzyme on graphene oxide electrodes

Graphene oxide sheets provide short-range electron transfer from the glucose oxidase enzyme to the electrode surface.

Cyclic voltammetric study of cobalt poly-4-t-butylpyridine ligand complexes on glassy carbon electrodes: electrolyte dependence and mechanistic considerations

Polypyridyl complexes of Co(II/III) have been gaining prominence as potential replacements for I(-)/I(3)(-) as mediators in dye sensitized solar cells. In that regard, homoleptic pseudo-octahedral complexes of 4,4'-di-t-butyl-2,2'-bipyridine, [Co(DTB)(3)](2+/3+), and 4,4',4″-tri-t-butyl-2,2':6,2″-terpyridine, [Co(TTT)(2)](2+/3+), have been of particular interest. These complexes show extreme electrode surface and electrolyte dependent electrochemical behavior. Below, we report on the cyclic voltammetric behavior of these two complexes at glassy carbon electrodes in two different electrolytes. The electrochemical data suggests that the Co(II/III) electron transfer is significantly nonadiabatic, especially for [Co(DTB)(3)](2+/3+) in LiClO(4) electrolyte.

Access to enhanced differences in Marcus-Hush and Butler-Volmer electron transfer theories by systematic analysis of higher order AC harmonics

The potential-dependences of the rate constants associated with heterogeneous electron transfer predicted by the empirically based Butler-Volmer and fundamentally based Marcus-Hush formalisms are well documented for dc cyclic voltammetry. However, differences are often subtle, so, presumably on the basis of simplicity, the Butler-Volmer method is generally employed in theoretical-experimental comparisons. In this study, the ability of Large Amplitude Fourier Transform AC Cyclic Voltammetry to distinguish the difference in behaviour predicted by the two formalisms has been investigated. The focus of this investigation is on the difference in the profiles of the first to sixth harmonics, which are readily accessible when a large amplitude of the applied ac potential is employed. In particular, it is demonstrated that systematic analysis of the higher order harmonic responses in suitable kinetic regimes provides predicted deviations of Marcus-Hush from Butler-Volmer behaviour to be established from a single experiment under conditions where the background charging current is minimal.

Study of the mechanism of catalytic activity of G. sulfurreducens biofilm anodes during biofilm growth

The number of investigations involving bioelectrochemical systems (BES), processes in which microorganisms catalyze electrode reactions, is increasing while their mechanisms remain unresolved. Geobacter sulfurreducens strain DL1 is a model electrode catalyst that forms multimicrobe-thick biofilms on anodes that catalyze the oxidation of acetate to result in an electric current. Here, we report the characterization by cyclic voltammetry (CV) of DL1 biofilm-modified anodes (biofilm anodes) performed during biofilm development. This characterization, based on our recently reported model of biofilm anode catalytic activity, indicates the following. 1) As a biofilm grows, catalytic activity scales linearly with the amount of anode-accessible redox cofactor in the biofilm. This observation is consistent with a catalytic activity that is limited during biofilm growth by electron transport from within cells to the extracellular redox cofactor. 2) Distinct voltammetric features are exhibited that reflect the presence of a redox cofactor expressed by cells that initially colonize an anode that is not involved in catalytic current generation.

Physical constraints on charge transport through bacterial nanowires

Extracellular appendages of the dissimilatory metal-reducing bacterium Shewanella oneidensis MR-1 were recently shown to sustain currents of 10(10) electrons per second over distances of 0.5 microns [El-Naggar et al., Proc. Natl. Acad. Sci. U. S. A., 2010, 107, 18127]. However, the identity of the charge localizing sites and their organization along the "nanowire" remain unknown. We use theory to predict redox cofactor separation distances that would permit charge flow at rates of 10(10) electrons per second over 0.5 microns for voltage biases of < or = IV, using a steady-state analysis governed by a non-adiabatic electron transport mechanism. We find the observed currents necessitate a multi-step hopping transport mechanism, with charge localizing sites separated by less than 1 nm and reorganization energies that rival the lowest known in biology.

Electrochemical and structural properties of a protein system designed to generate tyrosine Pourbaix diagrams

This report describes a model protein specifically tailored to electrochemically study the reduction potential of protein tyrosine radicals as a function of pH. The model system is based on the 67-residue α(3)Y three-helix bundle. α(3)Y contains a single buried tyrosine at position 32 and displays structural properties inherent to a protein. The present report presents differential pulse voltammograms obtained from α(3)Y at both acidic (pH 5.6) and alkaline (pH 8.3) conditions. The observed Faradaic response is uniquely associated with Y32, as shown by site-directed mutagenesis. This is the first time voltammetry is successfully applied to detect a redox-active tyrosine residing in a structured protein environment. Tyrosine is a proton-coupled electron-transfer cofactor making voltammetry-based pH titrations a central experimental approach. A second set of experiments was performed to demonstrate that pH-dependent studies can be conducted on the redox-active tyrosine without introducing large-scale structural changes in the protein scaffold. α(3)Y was re-engineered with the specific aim to place the imidazole group of a histidine close to the Y32 phenol ring. α(3)Y-K29H and α(3)Y-K36H each contain a histidine residue whose protonation perturbs the fluorescence of Y32. We show that these variants are stable and well-folded proteins whose helical content, tertiary structure, solution aggregation state, and solvent-sequestered position of Y32 remain pH insensitive across a range of at least 3-4 pH units. These results confirm that the local environment of Y32 can be altered and the resulting radical site studied by voltammetry over a broad pH range without interference from long-range structural effects.

Edge plane pyrolytic graphite electrode covalently modified with 2-anthraquinonyl groups: theory and experiment

An edge plane pyrolitic graphite (EPPG) electrode was modified by electrochemical reduction of anthraquinone-2-diazonium tetrafluoroborate (AQ2-N(2)(+)BF(4)(-)), giving an EPPG-AQ2-modified electrode of a surface coverage below a monolayer. Cyclic voltammograms simulated using Marcus-Hush theory for 2e(-) process assuming a uniform surface gave unrealistically low values of reorganisation energies, λ, for both electron transfer steps. Subsequently, two models of surface inhomogeneity based on Marcus-Hush theory were investigated: a distribution of formal potentials, E', and a distribution of electron tunneling distances, r(0). The simulation of cyclic voltammograms involving the distribution of formal potentials showed a better fit than the simulation with the distribution of tunneling distances. Importantly the reorganization energies used for the simulation of E' distribution were similar to the literature values for adsorbed species.