Reversible Redox Potential Research Articles

5,18‐Dimesitylorangarin: a Stable Antiaromatic [20]Pentaphyrin(1.0.1.0.0) Displaying Remarkable Oxidative Self‐Coupling Reactions

Abstract5,18‐Dimesitylorangarin and its BF2 complex were synthesized by double SNAr reaction of 3,5‐dibromo‐BODIPY with 2‐pyrrolydipyrrin as the first examples of meso‐aryl‐substituted orangarin. These orangarins, delineated as [20]pentaphyrin(1.0.1.0.0), are strongly antiaromatic but rather stable. The free base orangarin was coupled by oxidation with MnO2 to give a 11,11′‐linked dimer, a cyclooctatetraene(COT)‐centered trimer, and a spiro‐trimer. Fused COT‐centered 3H‐orangarin dimer was oxidized to the corresponding 2H‐orangarin dimer, which was further coupled to give a triply COT‐centered 2H‐orangarin tetramer. 3H‐Orangarin oligomers are all antiaromatic as evinced by extremely low‐field‐shifted 1H NMR signals of the inner NH and ill‐defined absorption spectra with broad tails. In contrast, COT‐centered 2H‐orangarin dimer and tetramer show moderately low‐field‐shifted NH signals and intense NIR absorbance over 900 nm, suggesting effective π‐conjugation through the COT bridge and almost non‐antiaromatic character. These orangarin oligomers exhibit many reversible redox potentials owing to the intramolecular electronic interactions. Regardless of the different aromatic characters, all the orangarin monomers and oligomers exhibit very rapid excited‐state decays.

5,18-Dimesitylorangarin: a Stable Antiaromatic [20]Pentaphyrin(1.0.1.0.0) Displaying Remarkable Oxidative Self-Coupling Reactions.

5,18-Dimesitylorangarin and its BF2 complex were synthesized by double SNAr reaction of 3,5-dibromo-BODIPY with 2-pyrrolydipyrrin as the first examples of meso-aryl-substituted orangarin. These orangarins, delineated as [20]pentaphyrin(1.0.1.0.0), are strongly antiaromatic but rather stable. The free base orangarin was coupled by oxidation with MnO2 to give a 11,11'-linked dimer, a cyclooctatetraene(COT)-centered trimer, and a spiro-trimer. Fused COT-centered 3H-orangarin dimer was oxidized to the corresponding 2H-orangarin dimer, which was further coupled to give a triply COT-centered 2H-orangarin tetramer. 3H-Orangarin oligomers are all antiaromatic as evinced by extremely low-field-shifted 1H NMR signals of the inner NH and ill-defined absorption spectra with broad tails. In contrast, COT-centered 2H-orangarin dimer and tetramer show moderately low-field-shifted NH signals and intense NIR absorbance over 900 nm, suggesting effective π-conjugation through the COT bridge and almost non-antiaromatic character. These orangarin oligomers exhibit many reversible redox potentials owing to the intramolecular electronic interactions. Regardless of the different aromatic characters, all the orangarin monomers and oligomers exhibit very rapid excited-state decays.

From Squaric Acid Amides (SQAs) to Quinoxaline-Based SQAs─Evolution of a Redox-Active Cathode Material for Organic Polymer Batteries.

The search for new redox-active organic materials (ROMs) is essential for the development of sustainable energy-storage solutions. In this study, we present a new class of cyclobuta[b]quinoxaline-1,2-diones or squaric acid quinoxalines (SQXs) as highly promising candidates for ROMs featuring exceptional stability and high redox potentials. While simple 1,2- and 1,3-squaric acid amides (SQAs), initially reported by Hünig and coworkers decades ago, turned out to exhibit low stability in their radical cation oxidation states, we demonstrate that embedding the nitrogen atoms into a quinoxaline heterocycle leads to robust two-electron SQX redox systems. A series of SQX compounds, as well as their corresponding radical cations, were prepared and fully characterized, including EPR spectroscopy, UV-vis spectroscopy, and X-ray diffraction. Based on the promising electrochemical properties and high stability of the new ROM, we developed SQX-functionalized polymers and investigated their physical and electrochemical properties for energy-storage applications. These polymers showed remarkable thermal stability well above 200 °C with reversible redox properties and potentials of about 3.6 V vs Li+/Li. By testing the galvanostatic cycling performance in half-cells with lithium-metal counter electrodes, a styrene-based polymer with SQX redox side groups showed stable cycling for single-electron oxidation for more than 100 cycles. These findings render this new class of redox-active polymers as highly promising materials for future energy-storage applications.

Synthesis, structures, electrochemical characterizations, theoretical and anticancer studies of Pd(II)-, Pt(II)- NHC complexes

We present the synthesis of two novel cationic Pd(II)- and Pt(II)- complexes ligated to a new C ∩ N donor N-heterocyclic carbene (NHC) ligand 3-methyl-1-(1-methyl-2-methylbenzoyl)imidazolin-2-ylidene, (1). Capitalizing 3-methyl-1-(1-methyl-2-methylbenzoyl)imidazolium hexafluorophosphate (1.HPF6), two novel isoelectronic and isostructural [Pd(1)2][PF6]2 (2), and [Pt(1)2][PF6]2 (3) complexes were synthesized. All the compounds were characterized by elemental analysis, 1H NMR, 13C NMR, IR, UV–Vis, mass spectroscopic studies, and finally single-crystal X-ray studies. X-ray crystallographic studies revealed both complexes 2 and 3 adopted square planar geometry. Electrochemical studies revealed Pt(II)/Pt(IV) reversible redox potential at 0.52 V. The catalytic activity of Pd(II)–NHC complex, 2 was tested for Suzuki coupling reactions. The structural assignments were further supported by DFT calculations. Molecular docking studies show a better binding affinity of 3 with Human-DNA Topoisomerase and BCL-2 protein compared to 2 and the scope of the complex 2 and 3 may be used as a drug. Cytotoxicity studies revealed that Pt(II)–NHC complex 3 is more potent than Pd(II)–NHC complex 2 against the breast cancer cell line (MCF-7) (IC50,7.9 ± 0.84 vs 6.0 ± 0.72 μM).

Unimolecular Chiral Stepping Inversion Machine.

Intelligent molecular machines that are driven by light, electricity, and temperature have attracted considerable interest in the fields of chemistry, materials, and biology. Herein, a unimolecular chiral stepping inversion molecular machine (SIMM) was constructed by a coupling reaction between dibromo pillar[5]arene and a tetrathiafulvalene (TTF) derivative (PT3 and PT5). Compared with the longer aliphatic linker PT5, PT3 with a shorter aliphatic linker shows chiral stepping inversion, achieving chiral inversion under a two-electron redox potential. Benefiting from the successive reversible two-electron redox potential of TTF, the self-exclusion and self-inclusion conformational transformations of SIMM can proceed in two steps under redox, leading to the chirality step inversion in the pillar[5]arene core. Electrochemical experiments and circular dichroism (CD) spectra show that the redox processes can cause SIMM CD signaling to reversibly switch. More importantly, as the oxidant Fe(ClO4)3 was increased from 0.1 to 1 equiv, the CD spectral signal of SIMM disappeared at 1 equiv, and further addition of Fe(ClO4)3 resulted in the CD signal reversed from positive to negative at 309 nm, indicating that the chirality was reversed after chemical oxidation and reached a negative maximum with the addition of 2 equiv Fe(ClO4)3; thus, redox-triggered chiral stepping inversion was achieved. Furthermore, the chiral inversion can be restored to its original state after the addition of 2 equiv of reducing agent, sodium ascorbate. This work demonstrates unimolecular chiral stepping inversion, providing a new perspective on stimulus-responsive chirality in molecular machines.

A Systematic Study on the Redox Potentials of Phenazine-Derivatives in Aqueous Media: A Combined Computational and Experimental Work.

Phenazines are an emerging class of organic compounds that have been recently utilized in aqueous redox flow batteries, a promising technology for large-scale energy storage. A virtual screening based on density functional theory calculations is used to investigate the redox potentials of around 100 phenazine derivatives in aqueous media containing various electron-donating or electron-withdrawing groups at different positions. The calculations identify the crucial positions that should be functionalized with multiple hydroxy groups to design new anolytes. The combined experimental-computational methodology reported herein guides the development of a new molecule with a record low reversible redox potential as a potential anolyte for aqueous redox flow batteries.

Sustainable Cathodes for Lithium‐Ion Energy Storage Devices Based on Tannic Acid—Toward Ecofriendly Energy Storage

AbstractThe use of organic materials with reversible redox activity holds enormous potential for next‐generation Li‐ion energy storage devices. Yet, most candidates are not truly sustainable, i.e., not derived from renewable feedstock or made in benign reactions. Here an attempt is reported to resolve this issue by synthesizing an organic cathode material from tannic acid and microporous carbon derived from biomass. All constituents, including the redox‐active material and conductive carbon additive, are made from renewable resources. Using a simple, sustainable fabrication method, a hybrid material is formed. The low cost and ecofriendly material shows outstanding performance with a capacity of 108 mAh g−1 at 0.1 A g−1 and low capacity fading, retaining approximately 80% of the maximum capacity after 90 cycles. With approximately 3.4 V versus Li+/Li, the cells also feature one of the highest reversible redox potentials reported for biomolecular cathodes. Finally, the quinone‐catecholate redox mechanism responsible for the high capacity of tannic acid is confirmed by electrochemical characterization of a model compound similar to tannic acid but without catecholic groups.

Deciphering electron-shuttling characteristics of epinephrine and dopamine for bioenergy extraction using microbial fuel cells

This first-attempt study provided novel electrochemical exploration via microbial fuel cells (MFCs), suggesting why catecholamine hormone-neurotransmitters epinephrine (EP) and dopamine (DA) could effectively trigger acute stress responses for humans. According to bioelectrochemical engineering, EP and DA are ortho-diphydroxyl (o-diOH) substituent(s)-bearing electron shuttles (ESs) that could effectively mediate electron-transfer capabilities for bioenergy extraction. This study quantitatively compared redox-mediating characteristics of EP and DA with other antioxidants and ESs, suggesting possible mechanisms of bioenergy-driven responses to organisms. Although some electrochemical activities of EP and DA were characterized in medical literature, this work clarified that EP and DA were also electrochemically favorable ESs for efficient bioenergy extraction. Compared to vitamin B2 (VB), vitamin C (VC) and gallic acid (GA), quantitative evaluation upon bioenergy-stimulating capabilities of EP and DA were clearly revealed via MFC modules. Apparently, both EP and DA as ESs significantly exhibited stable and reversible redox potential peaks in cyclic voltammetry. Evidently, power density performances of MFCs supplemented with EP and DA considerably increased ca. 127–385%, suggesting that DA and EP would be the most appropriate ESs to effectively stimulate electron-mediating capabilities in multicellular organisms. It was also suspected that highly efficient power-stimulating capabilities of DA and EP could be strongly associated with their electrochemically-steered disease-curative and life-threatening capabilities to humans.

A new NiCe complex derived from ortho-vanillin: Structural characterization and luminescence properties

In this study, a new heteronuclear NiCe complex [NiL2Ce(NO3)2(OAc)(H2O)(X)]·1.25H2O (where L = orthovanillinato; X: H2O or CH3OH) was prepared and characterised by analytical and spectroscopic methods. The molecular structure of the complex was further characterised by a single crystal X-ray diffraction study. In the structure of the complex there are four molecules in the asymmetric unit, with two having only water as coordinated solvent at the Ni(II) centre, and two others with part water and part methanol at this site. In the structure of the complex, a NiL2 moiety is bound to the Ce(III) ion via two phenolic and two methoxy oxygen atoms of two ligands L. The coordination sphere of the Ce(III) ion is completed by the coordination of oxygen atoms of two bidentate nitrate anions, an acetate which bridges the two metal ions, and a water ligand. Hirshfeld surface analysis was performed to investigate the inter-molecular contacts and their percentage contributions within the crystal packing. The complex molecules are linked by hydrogen bond contacts. The complex shows an emission band at 656 nm when excited at 317 nm with large Stokes shift. The complex exhibits a reversible redox potential at −0.36 V due to the cerium-based oxidation/reduction process.

Electrochemical Studies of the Pink-Phase Cu(im)2 (imH = imidazole) As a Cathode Material for Li-Ion Batteries

Compared to inorganic and metal- organic frameworks (IFs, MOFs) based on ions of transition metals such as Mn, Fe, Co, and Ni, Cu ion-based ones have been much less studied as cathode materials for Li-ion batteries (LIBs) and gained much less success. The main reason is that for almost all the studied materials, Cu2+ and Cu+ tend to be reduced to form metallic Cu and thus the frameworks tend to decompose during the discharge steps. We notice that in the vast majority of these compounds, be simple binary compounds, polyanionic (e.g. SO4 2- and PO4 3-) salts, or MOFs, Cu ions are coordinated by four to six O atoms. A couple of exceptions to the above statements include the recently developed Cu(2,7-AQDC) (AQDC = Anthraquinone- dicarboxylate)1 and the K0.1Cu[Fe(CN)6]0.7·3.8H2O/K0.1Ni[Fe(CN)6]0.7·4.1H2O core-shell structure.2 The Cu2+/Cu+ are coordinated by four O atoms and six N atoms, respectively and their Cu2+/Cu+ reversible redox potentials are 3.1 and 3.2 V vs. Li/Li+ respectively. We believe that in Cu(2,7-AQDC) three fused benzene rings in the anthra -quinone group play an important role in stabilizing the Cu2+/Cu+ redox pair. Therefore, we choose to investigate the electrochemical performances of Cu(im)2 (imH = imidazole) for three reasons. First, im can form stable compounds with both Cu2+ and Cu+.3–4. Second, unlike K0.1Cu[Fe(CN)6]0.7·3.8H2O, Cu(im)2 is non-toxic and the Cu-im bond plays a well-established role in biological systems. Third, the CuN4 coordination settings in all known Cu(im)2 phases and the aromatic heterocycle of im can help understand and develop N-containing ligands that can stabilize the Cu2+/Cu+ redox pair. The pink-phase Cu(im)2 (p-Cu(im)2) was prepared according to a published procedure.3 The experimental powder X-ray diffraction (PXRD) pattern match the reported (Fig. 1), indicating the formation of the desired product. Though p-Cu(im)2 afforded highly reproducible PXRD patterns, together with the broad peak features their complex patterns could not be indexed for exact structural determination. Despite its unknown structures so far, p-Cu(im)2 demonstrates interesting electro- chemical performances toward Li+ insertion and removal. In the first discharge, p-Cu(im)2 has a plateau at 2.17 V which should correspond to the reduction of Cu2+ into Cu+; it delivers a total of 54 mAh/g (Fig. 2a), about 40% of its theoretical capacity (136 mAh/g). In the subsequent first charge, there are a long plateau at ~2.67 V which should correspond to the oxidation of Cu+ into Cu2+; the potential gap between the discharge and charge plateaus is large (2.17 V vs. 2.67 V). There is also a short semi- plateau at ~3.40 V and the total charge capacity is 79 mAh/g. To understand the mechanism, ex-situ PXRD analysis (Fig. 2b) was used to track the electrode during cycling. When the electrode was soaked in the cell for 21 hrs. to reach equilibrium, discharged till the end of the discharge plateau, and discharged to 1.8 V, the peak positions and intensities from the framework remained almost unchanged, suggesting the framework remains intact; further there are no apparent formation of new phases. When it was charged back to 3.6 V, the peak intensities from the framework decreased significantly, suggesting the partial decomposition of the framework. It is likely some sort of phase changes and conversion occurs in the semi- plateau at 3.4 V during the first charge. In the subsequent cycling, both the charge and discharge capacities keep decreasing while the potentials of the charge and discharge plateaus are very close. The discharge capacity reaches 19 mAh/g in the fifth cycle. Though the first discharge capacity is only 40% of its theoretical capacity, p-Cu(im)2 appears not to decompose in the first discharge, agreeing with the conventional wisdom that im can stabilize both Cu2+ and Cu+. Ongoing investigations aim at (1) understanding the 40% fulfillment of the theoretical discharge capacity and the large potential gap between the charge and discharge plateaus in the first cycle and (2) finding out the optimal potential window for cycling. References Zhang, Z. Y.; Yoshikawa, H.; Awaga, K. J. Am. Chem. Soc. 2014, 136, 16112–16115.Asakura, D.; Li, C. H.; Mizuno, Y.; Okubo, M.; Zhou, H. S.; Talham, D. R. J. Am. Chem. Soc. 2013, 135, 2793–2799.Masciocchi, N.; Bruni, S.; Cariati, E.; Cariati, F.; Galli, S.; Sironi, A. Inorg. Chem. 2001, 40, 5897–5905.Huang, X. C.; Zhang, J. P.; Chen, X. M. Cryst. Growth & Des. 2006, 6, 1194–1198. Figure 1

Polyoxometalate/TiO2/Ag composite nanofibers with enhanced photocatalytic performance under visible light

The exploration of highly efficient and stable visible-light-driven photocatalysts for the wastewater treatment has been recognized as one of the currently most challenging topics for the environment remediation. In this paper, we report a new type of polyoxometalate-TiO2 composite nanofibers loaded with Ag nanoparticles (NPs), labeled as PMo12/TiO2/Ag-X (PMo12=[PMo12O40]3−; X represents the weight percent (%) of Ag in PMo12/TiO2/Ag samples; X=3.98, 5.41, 6.83, and 7.19 respectively). The SEM and TEM images manifest that the average diameter of the PMo12/TiO2 composite fibers is about 130±30nm, and the average size of Ag NPs is about 15±5nm. Photocatalytic experiments confirm that PMo12/TiO2/Ag catalysts display highly efficient and durable activity for the photodegradation of methyl orange (MO) and photoreduction of Cr(VI) under visible light irradiation (λ>420nm). In these composite series, PMo12/TiO2/Ag-5.41 exhibits the highest photocatalytic activity. The photocatalytic mechanism reveals that both Ag and PMo12 can be excited under visible light irradiation, which greatly improves the visible-light absorption of the composites. Furthermore, the introduction of POM species can not only improve the light adsorption and redox activity of the TiO2, but also promote the photochemical stability of the plasmonic composites because of the relatively narrow band gap and low reversible redox potential of polyoxoanion. Such POMs-based plasmon photocatalysts are important in ongoing efforts to designing and exploring of new photocatalytic materials with low cost, high efficiency, and durability.

Thienylquinonoidal Porphyrins and Hexaphyrins with Singlet Diradical Ground States.

To explore stable organic diradicaloids, meso-thienylquinonoid-substituted porphyrins Pn and hexaphyrins Hn, where "n" denotes the number of thienyl units in the meso-substituents, were synthesized. P0 was identified as a closed-shell quinonoid, whereas P1 was shown to possess significant diradical character with diradical character index (y) of 0.99 and quite small singlet-triplet energy gap (ΔES-T ) of -0.13 kcal mol-1 . P1 was certainly stable, allowing its isolation, but decomposed gradually in solution. In the hexaphyrin series, it was shown that H0 and H1 were closed-shell quinonoids, but H2 was a highly stable diradicaloid with y=0.85 and ΔES-T of -3.72 kcal mol-1 . The high stability of H2 was ascribed to effective spin delocalization over the entire conjugated network. Characteristically, H2 displays an intense absorption band in NIR region at λmax =1175 nm with molar absorption coefficient (ϵ) of 8.81×104 mol-1 L cm-1 , a narrow HOMO-LUMO gap of 0.69 eV, and nine reversible redox potential waves.

Multifunctional metallo porphyrin-imine conjugates: Photophysical, electrochemical, DNA binding and SOD enzyme mimetic studies

Abstract In this study, three new porphyrin-imine ligands (HA-HC) and their Cu(II), Fe(III) and Mn(III) complexes were prepared and characterized by the analytical and spectroscopic methods The substituent effects on the electronic and emission properties of the porphyrin-imine ligands were investigated in solutions. The electrochemical properties of the porphyrin-imine ligands and their metal complexes were investigated in DMF solution. The ligands showed reversible redox potentials in the positive regions. Superoxide dismutase (SOD) mimetic studies of the metal complexes of the porphyrin-imine ligands were investigated and the results of the complexes in this work showed higher activity than some reported SOD mimics. Finally, the DNA (fish sperm FSdsDNA) binding studies of the prepared compounds were investigated.

Simple Covalent Attachment of Redox‐Active Nitroxyl Radicals to Graphene via Diels‐Alder Cycloaddition

Here, this study reports a novel single‐step preparation of graphene functionalized by redox‐active nitroxyl radicals, a promising electrode material, without the requirement of graphite oxidation. Key feature of this concept is the Diels‐Alder [4+2] cycloaddition of dispersed graphene (DG), which has been obtained by shear‐induced solution exfoliation of graphite and functionalized maleimides as dienophiles. The redox‐active organic radical 2,2,6,6,‐tetramethylpiperdinyl‐1‐oxyl (TEMPO) is covalently attached by cycloaddition of DG with either N‐(1‐oxyl‐2,2,6,6,‐tetramethyl‐4‐piperidinyl)‐maleimide (TEMPO‐MI), or N‐(2,2,6,6‐tetramethyl‐piperidinyl)‐maleimide (TEMP‐MI), and subsequent oxidation. Successful product formation could be confirmed by high field Electron Paramagnetic Resonance (EPR) spectroscopy. Temperature‐dependent reaction monitoring by time‐resolved EPR in conjunction with Raman spectroscopy and elemental analysis results in an optimum cycloaddition temperature of 130 °C, at which 2.2 wt% TEMPO‐MI has been incorporated. However, owing to the limited thermal stability of TEMPO‐MI at temperatures above 100 °C, as again verified by EPR spectroscopy, the route via TEMP‐MI and subsequent oxidation is favored. Cyclovoltammetric evaluation of TEMPO‐functionalized graphene shows a reversible redox potential of +0.65 V as measured against Ag/AgCl, similar to that of TEMPO in solution. Hence, organic radical functionalized graphene derived by cycloaddition shows great potential for an easy production of electrodes that aim toward applications in organic energy storage devices. image

Highly active and stable heterogeneous catalysts based on the entrapment of noble metal nanoparticles in 3D ordered porous carbon

Heterogeneous catalysts that are prepared by immobilizing noble metal nanoparticles (NPs) on solid matrices can serve as efficient catalysts in various catalytic reactions. However, the immobilized NPs usually suffer from detachment or migration during the catalytic process owing to their weak interactions with the matrices. Here, we developed a facile approach for the synthesis of high active and stable heterogeneous catalysts by entrapping Pd and Ru NPs in 3D ordered hierarchically porous inverse opal carbon (IOC). For these catalysts, the 3D open-porous structure on multiple length scales provides the reactants easy access to the catalytically active NPs while the entrapment of NPs inside IOC ensures their high dispersion and stability during the catalysis. As a result, the as-prepared catalysts exhibited both high activity and stability for the oxidation of CO and electrocatalysis of VO2+/VO2+ redox couples. The conversion rate of CO over the IOC-PdNPs catalyst reached >98% at 200 °C, which showed no decrease after reacting for 10 h. The IOC-RuNPs-based working electrode exhibited highly reversible redox potentials at 1.25 V and 0.78 V, respectively, and no change of peak currents and peak potential separation were observed for 200 cycles of cyclic voltammetry (CV) measurements.

Kinetically Inert Bispidol-Based Cu(II) Chelate for Potential Application to (64/67)Cu Nuclear Medicine and Diagnosis.

A family of 2,4-pyridyl-disubstituted bispidol derivatives bearing methylene carboxylic acid ethyl esters (L1-L3), methylene carboxylic acids (L4 and L5), or methylenethiophene (L6) groups were synthesized. In water, all ligands form rigid 1:1 complexes in the presence of Zn(II) in which the bicycle adopts a chair-chair conformation (cis isomer), as observed by (1)H NMR and, in the case of ligand L1, by an X-ray diffraction crystal structure. Interestingly, addition of Zn(II) ions on ligand L1 induces a metal-mediated selective hydrolysis of the ethyl esters. This selective hydrolysis was not observed upon addition of other cations such as Na(+), Mg(+), and Ca(2+). Reduction of the central ketone was achieved to prevent ring opening via retro Diels-Alder reactions and to afford highly stable and water-soluble ligands (L4, L5, L6). The complexation properties of L4 and L6 were studied in solution, with a particular interest for ligand L4. Fast complexation occurs in strongly acidic media (pH = 1), with a high affinity toward Cu(II) (log KCuL4 = 19.2(3), pCu = 17.0 at pH 7.4, pCu = -log[Cufree], [Cu] = 1 × 10(-6) M, [L] = 1 × 10(-5) M) and high selectivity versus Co(II), Ni(II), and Zn(II), as shown by the values of the binding constants obtained from potentiometric and spectrophotometric titrations. Reversible redox potential with E1/2 = -430 mV (vs normal hydrogen electrode) was measured. The complex was found to be fairly inert from acid-assisted dissociation experiments in 5 M HClO4 (t1/2 = 110 d at 25 °C).

Covalent dimers of 1,3-diphenylisobenzofuran for singlet fission: synthesis and electrochemistry.

The synthesis of covalent dimers in which two 1,3-diphenylisobenzofuran units are connected through one phenyl substituent on each is reported. In three of the dimers, the subunits are linked directly, and in three others, they are linked via an alkane chain. A seventh new compound in which two 1,3-diphenylisobenzofuran units share a phenyl substituent is also described. These materials are needed for investigations of the singlet fission process, which promises to increase the efficiency of solar cells. The electrochemical oxidation and reduction of the monomer, two previously known dimers, and the seven new compounds have been examined, and reversible redox potentials have been compared with results obtained from density functional theory. Although the overall agreement is satisfactory, some discrepancies are noted and discussed.

High‐Throughput Mapping of the Electrochemical Properties of (Ni‐Fe‐Co‐Ce)Ox Oxygen‐Evolution Catalysts

AbstractDiscovering improved electrocatalysts is critical for many technologically important processes and for the development of new clean‐energy technologies. High‐throughput methods for measuring fundamental electrochemical properties are demonstrated through the investigation of oxygen‐evolution catalysis by using 665 oxide compositions containing nickel, iron, cobalt, and cerium. The behavior of each composition is characterized in 1.0 M NaOH(aq) by using a scanning drop three‐electrode cell to perform chronopotentiometry (CP) and cyclic voltammetry experiments. CP measurements at different current densities identify different composition–performance trends, owing to underlying variations in fundamental electrochemical behavior. We report systematic, coincident, composition‐dependent trends in the Tafel slopes and the reversible redox potentials of the catalysts. Applying high‐throughput electrochemical methods provides insight into composition–property–performance relationships and motivates new directions for the study of catalyst mechanisms by using informatics and theory.

The Electrochemical Approach towards Proton Coupled Electron Transfer Pathways for Oxidation of Thymine in Water

The work describes the use of cyclic voltammetry to investigate the proton coupled electron transfer (PCET) pathways for oxidation of thymine in water. Biologically important compounds like DNA bases, and amino acids showed irreversible behavior when oxidized electrochemically. The reversible redox potentials for such systems (say, irreversible electrochcemical systems) were estimated by analyzing the cyclic voltammograms recorded at different scan rates. The approach presents here is relatively simple and easy for obtaining reversible redox potential of electrochemically irreversible systems. Moreover, for the case of thymine, the obtained reversible oxidation potential also used to establish the PCET-pathways for oxidation of thymine in water.

A soluble bispentacenequinone precursor for creation of directly 6,6′-linked bispentacenes and a tetracyanobipentacenequinodimethane

We have synthesized 13,13′-(3,5-bis(trifluoromethyl)phenyl)-6,6′-bipentacene from a soluble bispentacenequinone precursor. Bispentacene takes orthogonal conformation in the solid state and exhibits four reversible redox potentials. In addition, a tetracyanobipentacenequinodimethane was obtained for the first time from the pure bispentacenequinone.