Electron Exchange Mechanism Research Articles

The survival strategy of direct interspecies electron transfer-capable coculture under electron donor-limited environments

Direct interspecies electron transfer (DIET) has been considered as an effective mechanism for interspecies electron exchange in microbial syntrophy. Understanding DIET-capable syntrophic associations under energy-limited environments is important because these conditions more closely approximate those found in natural subsurface environments than in the batch cultures in the laboratory. This study, investigated the metabolic dynamics and electron transfer mechanisms in DIET-capable syntrophic coculture of Geobacter metallireducens and Geobacter sulfurreducens under electron donor-limited condition. The wild-coculture and the mutant-coculture with a citrate synthase-deficient G. sulfurreducens exhibited similar rates of syntrophic metabolism under ethanol-limited and ethanol-replete conditions. Transcriptomic analyses revealed that, in the mutant-coculture in which interspecies electron exchange was the sole electron source for G. sulfurreducens, the transcription of genes associated with uptake hydrogenase in G. sulfurreducens were significantly repressed and thus DIET tended to be the preferred mode of interspecies electron exchange under electron donor-limited condition. To overcome electron donor limitation, c-type cytochromes in the coculture actively moved from outer membrane to extracellular environment, potentially via increased secretion of outer-membrane vesicles. These results suggested a preferred electron transfer mechanism for DIET-capable syntrophic communities' survival in the electron donor-limited environments, providing valuable insights into the biogeochemical processes mediated by DIET in natural and engineered environments.

Detection of Per‐ and Polyfluoroalkyl Substances (PFAS) by Interrupted Energy Transfer

AbstractThe ubiquitous presence of per‐ and polyfluoroalkyl substances (PFAS) in aqueous environments has aroused societal concern. Nonetheless, effective sensing technologies for continuous monitoring of PFAS within water distribution infrastructures currently do not exist. Herein, we describe a ratiometric sensing approach to selectively detect aqueous perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) at concentrations of μg ⋅ L−1. Our method relies on the excitonic transport in a highly fluorinated poly(p‐phenylene ethynylene) to amplify a ratiometric emission signal modulated by an embedded fluorinated squaraine dye. The electronic coupling between the polymer and dye occurs through overlap of π‐orbitals and is designed such that energy transfer is dominated by an electron‐exchange (Dexter) mechanism. Exposure to aqueous solutions of PFAS perturbs the orbital interactions between the squaraine dye and the polymer backbone, thereby diminishing the efficiency of the energy transfer and producing a “polymer‐ON/dye‐OFF” response. These polymer/dye combinations were evaluated in spin‐coated films and polymer nanoparticles and were able to selectively detect PFAS at concentrations of ca. 150 ppb and ca. 50 ppb, respectively. Both polymer films and nanoparticles are not affected by the type of water, and similar responses to PFAS were found in milliQ and well water.

Detection of Per- and Polyfluoroalkyl Substances (PFAS) by Interrupted Energy Transfer.

The ubiquitous presence of per- and polyfluoroalkyl substances (PFAS) in aqueous environments has aroused societal concern. Nonetheless, effective sensing technologies for continuous monitoring of PFAS within water distribution infrastructures currently do not exist. Herein, we describe a ratiometric sensing approach to selectively detect aqueous perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) at concentrations of μg ⋅ L-1 . Our method relies on the excitonic transport in a highly fluorinated poly(p-phenylene ethynylene) to amplify a ratiometric emission signal modulated by an embedded fluorinated squaraine dye. The electronic coupling between the polymer and dye occurs through overlap of π-orbitals and is designed such that energy transfer is dominated by an electron-exchange (Dexter) mechanism. Exposure to aqueous solutions of PFAS perturbs the orbital interactions between the squaraine dye and the polymer backbone, thereby diminishing the efficiency of the energy transfer and producing a "polymer-ON/dye-OFF" response. These polymer/dye combinations were evaluated in spin-coated films and polymer nanoparticles and were able to selectively detect PFAS at concentrations of ca. 150 ppb and ca. 50 ppb, respectively. Both polymer films and nanoparticles are not affected by the type of water, and similar responses to PFAS were found in milliQ and well water.

Study of the reaction mechanism in hydrogen production using metal-free Schiff base as a catalyst

Understanding the hydrogen evolution reaction and its mechanism is crucial for numerous practical applications in the realm of green energy. The development and discovery of new technologies or alternatives hold great significance in generating hydrogen at a low cost. In this study, we propose a novel catalyst, N, N'-bis(2-hydroxy-1-naphthaldehyde)-o-phenylenediamine ([naph]2-o-ph), which is a Schiff base, for hydrogen production. The novelty lies in utilizing the organic Schiff base system and the proposed mechanism for hydrogen evolution, involving protonation and electron exchange on the Schiff base. Both experimental and theoretical results highlight the high capability of the Schiff base in generating hydrogen, providing valuable insights for potential applications in water electrolysis.

Au13 Superatom Bearing Two Terpyridines at Coaxial Positions: Photoluminescence Quenching via Complexation with 3d Metal Ions

Abstract A gold cluster [Au13(dppe)5(EPTpy)2]3+ (dppe = 1,2-bis(diphenylphosphino)ethane, EPTpy-H = 4′-(4-ethynylphenyl)-2,2′:6′,2′′-terpyridine) was synthesized by ligand exchange reaction of [Au13(dppe)5Cl2]3+. Single-crystal X-ray diffraction analysis revealed that two terpyridyl moieties were σ-bonded to the coaxial positions of the icosahedral Au13 core. These two terpyridyl moieties were coordinated with 3d metal ions M2+ (M = Co, Ni, Cu, Zn) in acetonitrile solution under ambient conditions. The photoluminescence (PL) of [Au13(dppe)5(EPTpy)2]3+ with a quantum yield of 0.17 at ∼780 nm was almost completely quenched by coordination with Co2+, Ni2+, and Cu2+, while the PL was not affected by Zn2+ coordination. The metal-dependent PL quenching behavior is ascribed to the difference in the electronic structure of the metal ions. The energy transfer from the Au13 chromophore to the coordinated Co2+, Ni2+, or Cu2+ with an open electronic structure proceeds efficiently via an electron exchange mechanism, while the process is prohibited for Zn2+ with a closed electronic structure.

Solvent-Driven Self-Organization of Meso-Substituted Porphyrins: Morphological Analysis from Fluorescence Lifetime Imaging Microscopy.

A morphological analysis of different thin films of meso-tetra-p-(di-p-phenylamino)phenylporphyrin, H2T(TPA)4P, was made by fluorescence lifetime imaging microscopy (FLIM) and scanning electron microscopy (SEM). A comprehensive study of H2T(TPA)4P was undertaken through UV/vis absorption and fluorescence techniques in different solvents, solvent mixtures and in thin films. In solution, occurrence of intramolecular energy transfer from the triphenylamine (TPA) moieties to the porphyrin core, with quenching efficiencies in the order of 94-97%, is observed. The energy transfer rate constants are determined assuming Förster's dipole-dipole and Dexter's electron exchange mechanisms. In drop-cast-prepared thin films, from samples with different solvent mixtures, the photoluminescence (PL) quantum yield (ΦPL) decreases ∼1 order of magnitude compared to the solution behavior. FLIM and SEM experiments showed the self-organization and morphology of H2T(TPA)4P in thin films to be highly dependent on the solvent mixture used to prepare the film. In chloroform, the solvent's evaporation results in the formation of elongated and overlapped microrod structures. Introduction of a cosolvent, namely, a polar cosolvent, promotes changes in the morphology of the self-assembled structures, with the formation of three-dimensional spherical structures and hollow spheres. H2T(TPA)4P dispersed in a polymer matrix shows enhanced ΦPL values when compared to the drop-cast films. FLIM images showed coexistence of three different states or domains: aggregated, interface, and nonaggregated or less-aggregated states. This work highlights the importance of FLIM in the morphological characterization of heterogeneous films, together with the photophysical characterization of nano- and microdomains.

Ultrafast Charge-Transfer in Panchromatic, Push-Pull Porphyrin-Tetracyanobuta-1,3-Diene-Donor Conjugates

Light-induced electron transfer is a key step in solar energy conversion, and a process with myriad relevance in the fields of artificial photosynthesis, photocatalysis, photoconductivity, and molecular photovoltaics. In a donor-acceptor, D-A system, light absorption by a chromophore results in the formation of an excited state species, followed by a charge transfer between an electron donor (D) and an electron acceptor (A) leading to a charge-separated D .+ -A .- species.The optimization of these processes and comprehending their mutual interplay to ultimately achieve charge-separated species is of paramount importance for the development of efficient systems in solar light conversion schemes. As part of our continued effort in this field of research,1-3 using a combination of cycloaddition-retroelectrocyclization reaction, free-base and zinc porphyrins (H2P and ZnP) are decorated at their b-pyrrole positions with strong charge-transfer complexes, viz., tetracyanobuta-1,3-diene (TCBD)-DONOR as a novel class of push-pull systems.4 The physicochemical properties of these compounds have been investigated using a range of electrochemical, spectroelectrochemical, DFT as well as steady-state and time-resolved spectroscopic techniques. Charge transfer interactions between the porphyrin and the electron-withdrawing TCBD directly attached to the porphyrin p-system extended the absorption well into the near-infrared region. The occurrence of photoinduced charge transfer and separation has been established by complementary transient absorption spectral studies followed by global and target data analyses. The role of central metal in the porphyrin cavity and the nature of the donor in governing these photo events will be discussed. Khan, Y. Jang, Y. Patil, R. Misra, and F. D’Souza, Photoinduced Charge Separation Prompted Intervalence Charge Transfer in a Bis(thienyl)diketopyrrolopyrrole Bridged Donor-TCBD Push-Pull System (hot article), Angew. Chem. Int. Ed. 2021, 60, 20518–20527.S. Yadav, A. Z. Alsaleh,R. Misra and F. D’Souza, ‘Excited State Charge Transfer Leading to Charge Stabilization via an Electron Exchange Mechanism in Symmetric, Central Triphenylamine Derived, Dimethylaminophenyl-Tetracyanobutadiene Donor-Acceptor Conjugates, Chem. Sci. 2021, 12, 1109-1120.Pinjari, A. Z. Alsaleh,Y. Patil, R. Misra and F. D’Souza, Interfacing High-Energy Charge Transfer States to a Near-IR Sensitizer for Efficient Electron Transfer upon Near-IR Irradiation’ Angew. Chem. Int. Ed. 2020, 59, 23697-23705.Sekaran, A. Dawson, Y. Jang, K. V. MohanSingh, R. Misra and F. D’Souza, Charge-Transfer in Panchromatic Porphyrin-Tetracyanobuta-1,3-diene-Donor Conjugates: Switching the Role of Porphyrin in the Charge Separation Process, Chem. Eur. J. 2021, 27, 14335-14344 Figure 1

Electrochemical determination of ethanol on carbon paste electrode chemically modified with [N,N′-cis-1,2-cyclohexylene bis (salicylideneaminate)] nickel(II) Schiff base complex

This study describes two electroanalytical methods that employ a carbon paste electrode (CPE) chemically modified with [N,N′-cis-1,2-cyclohexylene-bis(salcylidenoaminate) nickel(II)] for ethanol oxidation—cyclic voltammetry (CV) and amperometry (AMP), both conducted in aqueous medium containing 1.0 mol L-1 NaOH as supporting electrolyte. For CV, potentials were scanned from 0.0 to + 0.8 V (vs Ag/AgCl) at 50 mV s−1; for AMP, the applied potential for ethanol oxidation was + 0.55 V (vs Ag/AgCl). During CPE modification, the CPE was heated with the [Ni(cis-salcn)] complex at 60 °C, to ensure paste agglutination. The [Ni(cis-salcn)] thermal stability was assessed by thermogravimetric analyses and differential scanning calorimetry, which demonstrated that the complex was stable up to 350 °C. Scanning electron microscopy and energy dispersive spectrometry revealed uniform [Ni(cis-salcn)] distribution on the chemically modified electrode surface. The proposed mechanism for electron exchange between ethanol and the electrode surface involved ethanol oxidation by the complex [(cis-salcn)(H2O)Ni(III)ONi(III)(OH)(cis-salcn)]– (Ni III), generated by electrochemical [Ni(cis-salcn)] activation in alkaline medium (1 mol L-1 NaOH). Ethanol was quantified by single-pulse amperometry, which showed linear dependence from 5 to 250 mmol L-1 with linear determination coefficient of 0.9918 ± 0.0058, average amperometric sensitivity of 1.33 μA L mmol−1, limit of detection of 0.75 mmol L-1, and limit of quantification of 2.50 mmol L-1. Therefore, compared to other nickel compounds reported in the literature, [Ni(cis-salcn)] displays good amperometric sensitivity, which is important for the development of techniques for electrochemical ethanol oxidation for diverse purposes.

A rainbow of acridinium chemiluminescence.

Multicolor chemiluminescent acridinium derivatives were synthesized by attaching various common fluorophores to the N10 -acridinium position through a piperazine linker. Triggering of each acridinium derivative using alkaline hydrogen peroxide resulted in a chemiluminescence spectrum dominated by a strong emission (>95%) from the attached fluorophore. The highly quenched emission from the triggered acridinium, acting as a donor, points to a highly efficient intramolecular energy transfer in acridinium-based chemiluminophore-fluorophore tandems. A variable, and in many cases minimal, spectral overlap between the donor emission and the acceptor absorption may indicate that in such tandems the energy transfer follows the Dexter electron exchange mechanism. Moreover, fluorophores affixed through the acridinium 9-position produce a typical acridinium emission profile, demonstrating the need for close distances and favorable intramolecular orientation of the donor and acceptor moieties for the energy transfer to occur. A family of red-shifted chemiluminescent labels, all sharing a uniform triggering method, will find immediate application in multicolor ligand-receptor assays. Along with the multiplexing capabilities, the red-shifted chemiluminescent detection offers a higher tolerance to green-colored biological interferences and will therefore benefit many screening and diagnostic clinical tests.

Magnesium Ferrite/Polyvinyl Alcohol (PVA) Nanocomposites: Fabrication and Characterization

Terbium doped magnesium spinel ferrites (Mg1-xTbxFe2O4) with composition x=0.12, 0.14, 0.16, 0.18 were synthesized via micro-emulsion method followed by synthesis of PVA/Mg1-xTbxFe2O4 composites using in-situ polymerization technique. The structural properties were evaluated using X-ray diffraction (XRD) and Fourier transform infra-red spectroscopy (FTIR). XRD analysis confirmed the construction of spinel lattice of terbium ferrite whereas FTIR revealed the interactions between ferrite nanoparticles and polyvinyl alcohol matrix. The XRD and FTIR results quite matched with the reported literature. The dielectric and resistivity analyses were performed by determining dielectric parameters and current-voltage measurements. The values of dielectric constant, dielectric loss and tan ? were found to be inversely proportional to the frequency under the ambient electric field at room temperature but became constant at higher frequency values. The lower values of dielectric constant of terbium incorporated magnesium ferrite polymer composites (MgFe2O4/PVA) are attributed to hindrance in ‘electron exchange mechanism’ created by lockup between iron and terbium ions. The resistivity values of all the composites were found from 2.5x109 ?cm to 18.8x109 ?cm which showed a non- linear behavior.

Electrical characterization of near-interface traps in thermally oxidized and NO-annealed SiO2/4H-SiC metal-oxide-semiconductor capacitors

Conductance method and capacitance-voltage (C-V) measurements are used to detect and analyze the characteristics of traps in thermally oxidized and NO-annealed SiO2/4 H-SiC-based metal-oxide-semiconductor (MOS) structures, which have energy levels near the conduction band edge (EC) of 4 H-SiC. The near-interface traps (NITs) located within SiO2 near the SiO2/4 H-SiC interface, which have a strong effect on the mobility and reliability of the MOS devices, are separated from the interface traps. According to the bias state of the MOS capacitors, two types of electron exchange mechanisms between the energy level of NITs and EC of 4 H-SiC are proposed. The influence of NITs on the (C-V) and conductance characteristics of the MOS capacitors is studied. The possible effect of NITs on the performance of electronic devices containing a MOS capacitor is predicted.

Direct vs Delayed Triplet Energy Transfer from Organic Semiconductors to Quantum Dots and Implications for Luminescent Harvesting of Triplet Excitons.

Hybrid inorganic–organic materials such as quantum dots (QDs) coupled with organic semiconductors have a wide range of optoelectronic applications, taking advantage of the respective materials’ strengths. A key area of investigation in such systems is the transfer of triplet exciton states to and from QDs, which has potential applications in the luminescent harvesting of triplet excitons generated by singlet fission, in photocatalysis and photochemical upconversion. While the transfer of energy from QDs to the triplet state of organic semiconductors has been intensely studied in recent years, the mechanism and materials parameters controlling the reverse process, triplet transfer to QDs, have not been well investigated. Here, through a combination of steady-state and time-resolved optical spectroscopy we study the mechanism and energetic dependence of triplet energy transfer from an organic ligand (TIPS-tetracene carboxylic acid) to PbS QDs. Over an energetic range spanning from exothermic (−0.3 eV) to endothermic (+0.1 eV) triplet energy transfer we find that the triplet energy transfer to the QD occurs through a single step process with a clear energy dependence that is consistent with an electron exchange mechanism as described by Marcus–Hush theory. In contrast, the reverse process, energy transfer from the QD to the triplet state of the ligand, does not show any energy dependence in the studied energy range; interestingly, a delayed formation of the triplet state occurs relative to the quantum dots’ decay. Based on the energetic dependence of triplet energy transfer we also suggest design criteria for future materials systems where triplet excitons from organic semiconductors are harvested via QDs, for instance in light emitting structures or the harvesting of triplet excitons generated via singlet fission.

Syntrophus conductive pili demonstrate that common hydrogen-donating syntrophs can have a direct electron transfer option.

Syntrophic interspecies electron exchange is essential for the stable functioning of diverse anaerobic microbial communities. Hydrogen/formate interspecies electron transfer (HFIT), in which H2 and/or formate function as diffusible electron carriers, has been considered to be the primary mechanism for electron transfer because most common syntrophs were thought to lack biochemical components, such as electrically conductive pili (e-pili), necessary for direct interspecies electron transfer (DIET). Here we report that Syntrophus aciditrophicus, one of the most intensively studied microbial models for HFIT, produces e-pili and can grow via DIET. Heterologous expression of the putative S. aciditrophicus type IV pilin gene in Geobacter sulfurreducens yielded conductive pili of the same diameter (4 nm) and conductance of the native S. aciditrophicus pili and enabled long-range electron transport in G. sulfurreducens. S. aciditrophicus lacked abundant c-type cytochromes often associated with DIET. Pilin genes likely to yield e-pili were found in other genera of hydrogen/formate-producing syntrophs. The finding that DIET is a likely option for diverse syntrophs that are abundant in many anaerobic environments necessitates a reexamination of the paradigm that HFIT is the predominant mechanism for syntrophic electron exchange within anaerobic microbial communities of biogeochemical and practical significance.

Highly Efficient One-Dimensional Triplet Exciton Transport in a Palladium-Porphyrin-Based Surface-Anchored Metal-Organic Framework.

Efficient photon-harvesting materials require easy-to-deposit materials exhibiting good absorption and excited-state transport properties. We demonstrate an organic thin-film material system, a palladium-porphyrin-based surface-anchored metal-organic framework (SURMOF) thin film that meets these requirements. Systematic investigations using transient absorption spectroscopy confirm that triplets are very mobile within single crystalline domains; a detailed analysis reveals a triplet transfer rate on the order of 1010 s-1. The crystalline nature of the SURMOFs also allows a thorough theoretical analysis using the density functional theory. The theoretical results reveal that the intermolecular exciton transfer can be described by a Dexter electron exchange mechanism that is considerably enhanced by virtual charge-transfer exciton intermediates. On the basis of the photophysical results, we predict exciton diffusion lengths on the order of several micrometers in perfectly ordered, single-crystalline SURMOFs. In the presently available samples, strong interactions of excitons with domain boundaries present in these metal-organic thin films limit the diffusion length to the diameter of these two-dimensional grains, which amount to about 100 nm. Our results demonstrate high potential of SURMOFs for light-harvesting applications.

Exploration of the PET‐RAFT Initiation Mechanism for Two Commonly Used Photocatalysts

AbstractAn investigation into the PET‐RAFT initiation mechanism (photoinduced electron/energy transfer‐reversible addition‐fragmentation chain transfer) for two frequently used photocatalysts with five RAFT agents has been conducted through analysis of electron transfer and triplet energy transfer (electron exchange) pathways. The electronic and redox properties of the studied RAFT agents were determined through quantum mechanical calculations and cyclic voltammetry measurements, respectively. Gibbs free energy changes for both electron transfer and electron exchange mechanisms were then calculated and compared to quenching rate constants determined by laser flash photolysis (LFP). Transient absorption spectra for the photocatalyst‐RAFT agent combinations were also measured by LFP to substantiate the energetics considerations, which show that triplet energy transfer through a Dexter electron exchange mechanism for the activation of RAFT agents is probable. The experimental data has been fitted by Balzani's energy transfer model which provides support for a Dexter electron exchange mechanism in these systems.

Geobacter Strains Expressing Poorly Conductive Pili Reveal Constraints on Direct Interspecies Electron Transfer Mechanisms

ABSTRACTCytochrome-to-cytochrome electron transfer and electron transfer along conduits of multiple extracellular magnetite grains are often proposed as strategies for direct interspecies electron transfer (DIET) that do not require electrically conductive pili (e-pili). However, physical evidence for these proposed DIET mechanisms has been lacking. To investigate these possibilities further, we constructed Geobacter metallireducens strain Aro-5, in which the wild-type pilin gene was replaced with the aro-5 pilin gene that was previously shown to yield poorly conductive pili in Geobacter sulfurreducens strain Aro-5. G. metallireducens strain Aro-5 did not reduce Fe(III) oxide and produced only low current densities, phenotypes consistent with expression of poorly conductive pili. Like G. sulfurreducens strain Aro-5, G. metallireducens strain Aro-5 displayed abundant outer surface cytochromes. Cocultures initiated with wild-type G. metallireducens as the electron-donating strain and G. sulfurreducens strain Aro-5 as the electron-accepting strain grew via DIET. However, G. metallireducens Aro-5/G. sulfurreducens wild-type cocultures did not. Cocultures initiated with the Aro-5 strains of both species grew only when amended with granular activated carbon (GAC), a conductive material known to be a conduit for DIET. Magnetite could not substitute for GAC. The inability of the two Aro-5 strains to adapt for DIET in the absence of GAC suggests that there are physical constraints on establishing DIET solely through cytochrome-to-cytochrome electron transfer or along chains of magnetite. The finding that DIET is possible with electron-accepting partners that lack highly conductive pili greatly expands the range of potential electron-accepting partners that might participate in DIET.

Synthesis, photoluminescence, and energy transfer mechanism of a reactive Eu(III)-complex used in white light-emitting diodes

A reactive Eu(III)-complex Eu(TTA)3 ( UA ) was synthesized with 2-thenoyltrifluoroacetone (TTA) as primary ligand and undecylenic acid (UA) as active ligand. The structure of the complex was characterized by elemental analysis, FT-IR spectra, and UV–vis absorption spectra. The results indicate that the Eu(III) ion is successfully coordinated with primary ligand TTA and active ligand UA. Fluorescence spectra suggest that the complex exhibits excellent red emission of Eu(III) ion with a peak at 611 nm being monitored at 365 nm of near ultraviolet. Meanwhile, the complex has also shown a long fluorescence lifetime of 1.4259 ms and a high quantum yield of 86.7%. The singlet and triplet energy levels for the ligands of rare earth complexes were calculated using Gaussian 03 program package. Intramolecular energy transfer diagram was established and an energy transfer process following Dexter electron exchange mechanism was demonstrated, which provides the experimental data and theoretical foundation for the development of high-performance luminescent materials. The result of TGA shows that the complex keeps stable at 156°C or below. All the results demonstrate that the reactive Eu(III)-complex can be used as the red-light material in white light-emitting diodes phosphor.

Azophenine as Central Core for Efficient Light Harvesting Devices.

The notoriously non-luminescent uncycled azophenine (Q) was harnessed with Bodipy and zinc(II)porphyrin antennas to probe its fluorescence properties, its ability to act as a singlet excited state energy acceptor and to mediate the transfer. Two near-IR emissions are depicted from time-resolved fluorescence spectroscopy, which are most likely due to the presence of tautomers of very similar calculated total energies (350 cm-1 ; DFT; B3LYP). The rates for energy transfer, kET (S1 ), for 1 Bodipy*→Q are in the order of 1010 -1011 s-1 and are surprisingly fast when considering the low absorptivity properties of the lowest energy charge transfer excited state of azophenine. The rational is provided by the calculated frontier molecular orbitals (MOs) which show atomic contributions in the C6 H4 C≡CC6 H4 arms, thus favoring the double electron exchange mechanism. In the mixed-antenna Bodipy-porphyrin star molecule, the rate for 1 Bodipy*→porphyrin has also been evaluated (≈16×1010 s-1 ) and is among the fastest rates reported for Bodipy-zinc(II)porphyrin pairs. This astonishing result is again explained from the atomic contributions of the C6 H4 C≡CC6 H4 and C≡CC6 H4 arms thus favouring the Dexter process. Here, for the first time, this process is found to be sensitively temperature-dependent. The azophenine turns out to be excellent for electronic communication.

Mediator Effects on Solid-State Mediator Doped Polymer Electrolyte Membrane

Electrolyte and separator are two vital components in supercapacitors. High safety is one of the major advantages of polymer electrolyte, which means, even in extreme environment or during faulty, polymer electrolyte will not release any harmful gas or liquid. Mediators are a pair of compounds which can reciprocal transform by losing and gaining electrons. Thus, doping mediators in polymer electrolyte will improve the electronic conductivity. Use of the mediator doped electrolytes in the electrode matrix will benefit the transport process in supercapacitors. However, these electrolytes should not be used in the separators. Polyvinylidene fluoride (PVDF) and lithium trifluoromethanesulfonate (LiTFS) was selected as polymer electrolyte. One mediator couple are potassium ferrocyanide (K3Fe(CN)6) and potassium ferricyanide (K4Fe(CN)6). Another couple are iodine (I2) and sodium iodide (NaI). Conductivity of the membranes were measured with an device as shown in Figure 1. Results of electronic conductivity versus the concentration of mediators are given in Figure 2 and results of ionic conductivity versus the concentration of mediators are given in Figure 3. Electronic conductivity of membranes is enhanced from 10-7 S/cm level to 10-4 S/cm level by increasing the concentration of mediators from 0% to 5%. In the I2/NaI mediator doped membrane the electronic conductivity continuously increase with increasing the concentration above 5%. However, in the K3Fe(CN)6/ K4Fe(CN)6. doped membrane the electronic conductivity is a constant above 5%. Ionic conductivity of membranes is stayed on 10-2 S/cm level. The authors use the electron exchange mechanism and site percolation theory to explain the phenomenon. Figure 1

The effect that comparing molecular animations of varying accuracy has on students’ submicroscopic explanations

In this qualitative study, we examined how a group of seventeen first semester General Chemistry students responded when they were shown contrasting molecular animations of a reduction–oxidation (redox) reaction between solid copper and aqueous silver nitrate for which they first viewed a video of the actual experiment. The animations contrasted in that they portrayed different reaction mechanisms for the redox reaction. One animation was scientifically accurate and reflected an electron exchange mechanism, while the other was purposefully inaccurate and represented a physical exchange between the ions. Students were instructed to critique each animation for its fit with the experimental evidence and to ultimately choose the animation that they felt best depicted the molecular level of the chemical reaction. Analyses showed that most students identified that the electron exchange animation was the more scientifically accurate animation; however, approximately half of the students revised their drawings to fit with the inaccurate physical exchange animation. In addition, nearly all students thought that both animations were correct and useful for understanding salient information about the redox reaction. The results indicate that when students are shown contrasting animations of varying accuracy they make errors in deciding how the animations are supported and refuted by the evidence, but the treatment is effective. Contrasting animations promote students to think deeply about how animations fit with experimental evidence and is a promising way to engage students to think deeply about animations.