Pairs Of Reversible Redox Waves Research Articles

Dual-Redox System of Metallo-Supramolecular Polymers for Visible-to-Near-IR Modulable Electrochromism and Durable Device Fabrication

Dual-redox metallo-supramolecular polymers with a zigzag structure (polyFe-N and polyRu-N) were successfully synthesized by 1:1 complexation of a redox-active Fe(II) or Ru(II) ion and 4,4-bis(2,2:6,2-terpyridinyl)phenyl-triphenylamine (LTPA) as a redox-active ligand. The polymers had high solubility in methanol, and the polymer solutions showed dark brown (polyFe-N) or orange-red (polyRu-N) coloration. UV-vis spectra of the polymers displayed a strong metal-to-ligand charge transfer (MLCT) absorption in the visible region. Cyclic voltammograms of the polymer films exhibited two pairs of reversible redox waves. The first redox at ∼0.5 V versus Ag/Ag+ was assigned to the redox in the triphenylamine (TPA) moiety of LTPA, and the second redox at 0.8 V versus Ag/Ag+ (polyFe-N) or 0.9 V versus Ag/Ag+ (polyRu-N) was given to the redox of Fe(II)/(III) or Ru(II)/(III), respectively. Upon applying a positive potential of more than 0.5 V versus Ag/Ag+ to the polymer films, a new absorption at ∼820 nm in the near-infrared (NIR) region appeared with wide tailing to the longer wavelength. It is considered that the new absorption in the NIR region is caused by the polaron band of the oxidized ligand in the polymers. When the applied potential was increased to 1.0 V versus Ag/Ag+ (polyFe-N) or 1.1 V versus Ag/Ag+ (polyRu-N), the maximum wavelength of the new absorption in the NIR region shifted to 885-900 nm and the absorbance was further enhanced with disappearance of the MLCT absorption. Eventually, the original colors of the polymers were faint to light green. This visible-to-NIR electrochromism was reversible, and maximum optical contrast (ΔT) reached 52% in the visible region and 80% in the NIR region. A prototype solid-state device with the polymer was fabricated for practical utilization, exhibiting excellent cycle stability of >4000 cycles with maintaining high optical contrast from the visible-to-NIR range.

Synthesis and properties of electroactive aromatic polyimides with methyl- or trifluoromethyl-protecting triphenylamine units

Two series of new redox-active aromatic polyimides with methyl- (–CH3) or trifluoromethyl (–CF3)-protecting triphenylamine moieties were prepared from 4,4′-diamino-4″-methyltriphenylamine and 4,4′-diamino-4″-(trifluoromethyl)triphenylamine with aromatic tetracarboxylic dianhydrides via the conventional two-step polycondensation technique. Flexible and strong polyimide films could be obtained via the thermal curing of their precursor poly(amic acid) films or direct solution cast from some organosoluble polyimides. The polyimides showed high glass-transition temperatures between 269°C and 312°C, and they did not show significant decomposition before 500°C in air or under nitrogen atmosphere. Cyclic voltammograms of the polyimide films on the indium–tin oxide-coated glass substrate exhibited a pair of reversible redox waves with half-wave oxidation potentials of 1.08–1.10 V (for the –CH3 series) and 1.23–1.26 V (vs. silver/silver chloride; for the –CF3 series) in acetonitrile solution. The polyimide films showed anodic electrochromism from pale yellow neutral state to purplish blue (for the –CH3 series) and chrome yellow (for the –CF3 series) when oxidized.

Electron transfer mechanism of cytochrome c at graphene electrode

We report the direct electron transfer of cytochrome c (Cyt c) observed at graphene electrodes. Graphene nanosheets were chemically synthesized and immobilized on to a glassy carbon electrode. Cyclic voltammetry of Cyt c in phosphate buffered saline was performed at these electrodes. Results indicated a pair of reversible redox waves with a peak-to-peak separation value of 0.07 V in a diffusion controlled electrochemical process. Furthermore, the voltammetric response of these electrodes in Cyt c were found to be stable over time with negligible electrode fouling toward Cyt c.

Direct electrochemistry and electrocatalysis of hemoglobin protein entrapped in graphene and chitosan composite film

A novel, biocompatible sensing strategy based on graphene and chitosan composite film for immobilizing the hemoglobin protein was firstly adopted. The direct electron transfer and bioelectrocatalytic activity of hemoglobin after incorporation into the composite film were investigated. A pair of reversible redox waves of hemoglobin was appeared, and hemoglobin could exhibit its bioelectrocatalytic activity toward H(2)O(2) in a long term. Such results indicated that graphene and chitosan composite could be a friendly biocompatible interface for immobilizing biomolecules and keeping their native structure. Furthermore, the appearance of graphene in the composite film could facilitate the electron transfer between matrix and the electroactive center of hemoglobin. Hence, this graphene and chitosan based protocol would be a promising platform for protein immobilization and biosensor preparation.

Synthesis and characterization of novel electroactive polyamides and polyimides with bulky 4‐(1‐adamantoxy)triphenylamine moieties

AbstractA novel adamantoxytriphenylamine‐containing diamine monomer, 4‐(1‐adamantoxy)‐4′,4″‐diaminotriphenylamine, was synthesized from readily available reagents. Two series of novel electroactive aromatic polyamides and polyimides with bulky 4‐(1‐adamantoxy)triphenylamine moieties were prepared from the newly synthesized diamine monomer with various aromatic dicarboxylic acids and tetracarboxylic dianhydrides, respectively. All the resulting polyamides and most of the polyimides were readily soluble in polar organic solvents and could be solution cast into tough and flexible films. These polymers showed moderate to high glass transition temperatures in the range of 263–311 °C, and they were fairly stable up to a temperature above 480 °C (for polyamides) or 500 °C (for polyimides). Cyclic voltammograms of the polyamides and polyimides showed one pair of reversible redox waves with oxidation half‐wave potentials (E1/2) in the range of 0.78–0.81 and 0.97–1.05 V, respectively, versus Ag/AgCl in an acetonitrile solution. In addition, the polymers were found to display stable electrochromic properties by repeated cyclic scans between 0.0 and 1.1–1.2 V, with coloration change from a colorless or pale yellowish neutral form to a dark blue or bluish green oxidized form. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1740–1755, 2009

Synthesis, structures and properties of new organic donors connecting to a TEMPO radical through a pyrrolidine ring

We report the synthesis, structures and physical properties of new TEMPO-containing electron donors in which a TEMPO radical part connects to the EDT-TTF ( 1) or EDO-TTF ( 2) skeletons through a pyrrolidine ring. The donors are paramagnetic and showed a slight antiferromagnetic interaction at low temperature region. The CV measurement showed two pairs of reversible redox waves originated from the TTF part and one oxidation wave from the TEMPO radical part. Physical properties of the iodine complex of 1 are also presented.

New organic conductors based on tellurium-containing donor molecules

Trimethyleneditelluro- and trimethyleneoxaditelluro-substituted dimethyl-TTF derivatives were prepared. The CV result of the trimethyleneditelluro-substituteddimethyl-TTF derivative shows characteristic multi-redox behavior and the trimethyleneoxaditelluro-substituted dimethyl-TTF derivative exhibits two pairs of reversible redox waves. The structures and physical properties of conducting salts based on their donors are also clarified.

Synthesis and properties of a new TSeF derivative containing a pyrazino-ring

A novel pyrazino-fused TSeF donor molecule 1 was synthesized. The donor 1 showed two pairs of reversible redox waves (+0.85 and +1.18 V vs. Ag/AgCl in PhCN). Many cation radical salts containing tetrahedral or octahedral anions showed metallic conducting behavior down to low temperature. Among them, the BF 4 - and ClO 4 - salts have unique donor arrangements, similar to the β-like structure and 2:1 donor-to-anion composition. These salts are two-dimensional conductors with a strong intermolecular interaction along the side-by-side direction of the donor molecule.

Synthesis and properties of a new organic donor containing a TEMPO radical

Recently we have studied the interplay between conductivity and magnetism by means of new organic donors containing a stable TEMPO radical. In this work, we have prepared a novel electron donor I in which a TEMPO radical part connects to the EDT-TTF skeleton through a pyrrolidine ring. The ESR spectra of 1 indicated three absorption lines (g =2.0062, aN = 15.5 G) characteristic of TEMPO radical. The donor I is paramagnetic and showed antiferromagnetic interaction at low temperature region (θ = -2.4 K). The CV measurement revealed I shows two pairs of reversible redox waves (+0.48 and +0.86 V vs. Ag/AgCl) and one oxidation wave (+0.83 V).

Synthesis and properties of new organic donor containing organic radical part

Recently interplay between conductivity and magnetism has been focused in the research of new organic conductors. In this work, novel electron donor TEMPOET which is consisted of the extended TTF skeleton and stable TEMPO radical part was synthesized. The ESR spectra of TEMPOET indicated three absorption lines (g =2.0062, a N = 15.1 G) characteristic of the TEMPO radical. It is revealed that TEMPOET shows paramagnetic susceptibility corresponding to one spin per molecule and slightly antiferromagnetic interaction at low temperature region (θ = −1.00 K). The CV measurement revealed TEMPOET shows one pair of reversible redox waves (0.88 V vs. Ag/AgCl) and three pairs of irreversible ones (+0.56, +1.17, +1.77V).