Oxidative Electropolymerization Research Articles

Electropolymerization of a New Diketopyrrollopyrrole Derivative into Inherent Chiral Polymer Films

Electropolymerization is a convenient way to obtain conducting polymers (CPs) directly adhered to an electrode surface. CPs are well-known for their various application fields in photovoltaic cells, chemical sensors, and electronics. By implementing chirality into a CP, the application possibilities will spread further onto chiral sensors or optoelectronics. In this work, we introduce a new inherently chiral polymer based on a macrocyclic 3,4-ethylenedioxythiophene-diketopyrrolopyrrole-3,4-ethylenedioxythiophene triad (EDOT-DPP-EDOT) fused by 1,4-phenylene groups, which was prepared via oxidative electropolymerization directly on the electrode surface. The investigation of the chiroptical properties was performed by circular dichroism spectroscopy in the solid state. The enantiomeric pure polymer films obtained showed dissymmetry factors of up to −2.71 × 10−4, whereby linear dichroism contributions can be widely excluded.

Synthesis and Structure-Property Relationship of meso-Substituted Porphyrin- and Benzoporphyrin-Thiophene Conjugates toward Electrochemical Reduction of Carbon Dioxide.

A novel series of ZnII-trans-A2B2 porphyrins and benzoporphyrins bearing phenyl and thiophene-based meso-substituents was successfully synthesized and characterized by spectroscopic and electrochemical techniques. Systematic comparison among the compounds in this series, together with the corresponding A4 analogs previously studied by our group, led to the understanding of the effects of π-conjugated system extension of a porphyrin core through β-fused rings, replacement of the phenyl with the thiophene-based meso-groups, and introduction of additional thiophene rings on thienyl substituents on photophysical and electrochemical properties. Oxidative electropolymerization through bithiophenyl units of both A4 and trans-A2B2 analogs was achieved, resulting in porphyrin- and benzoporphyrin-oligothiophene conjugated polymers, which were characterized by cyclic voltammetry and absorption spectrophotometry. Preliminary studies on catalytic performance toward electrochemical reduction of carbon dioxide (CO2) was described herein to demonstrate the potential of the selected compounds for serving as homogeneous and heterogeneous electrocatalysts for the conversion of CO2 to carbon monoxide (CO).

Polymerized Riboflavin and Anthraquinone Derivatives for Oxygen Reduction Reaction

AbstractHydrogen peroxide (H2O2) is identified as a promising reagent for fuel cells, reducing the dependency on carbon‐based fuels. In this work, electrochemically synthesized polymers are employed to improve the efficiency of the oxygen (O2) reduction reaction, thus producing H2O2 in an environmentally friendly way. Two aminoanthraquinones, as well as riboflavin (vitamin B2), are successfully immobilized via oxidative electropolymerization onto both glassy carbon and carbon paper. Of the investigated compounds, polyriboflavin shows a high Faradaic efficiency toward O2 reduction, even at a very low potential of only −0.1 V versus SHE. This catalytic effect is present in neutral and alkaline conditions, using both glassy carbon and carbon paper, but highly pronounced in neutral, aqueous solutions.

Enhancing Photoredox Catalysis in Aqueous Environments: Ruthenium Aqua Complex Derivatization of Graphene Oxide and Graphite Rods for Efficient Visible-Light-Driven Hybrid Catalysts.

A ruthenium aqua photoredox catalyst has been successfully heterogeneneized on graphene oxide (GO@trans-fac-3) and graphite rods (GR@trans-fac-3) for the first time and have proven to be sustainable and easily reusable systems for the photooxidation of alcohols in water, in mild and green conditions. We report here the synthesis and total characterization of two Ru(II)-polypyridyl complexes, the chlorido trans-fac-[RuCl(bpea-pyrene)(bpy)](PF6) (trans-fac-2) and the aqua trans-fac-[Ru(bpea-pyrene)(bpy)OH2](PF6)2 (trans-fac-3), both containing the N-tridentate, 1-[bis(pyridine-2-ylmethyl)amino]methylpyrene (bpea-pyrene), and 2,2'-bipyridine (bpy) ligands. In both complexes, only a single isomer, the trans-fac, has been detected in solution and in the solid state. The aqua complex trans-fac-3 displays bielectronic redox processes in water, assigned to the Ru(IV/II) couple. The trans-fac-3 complex has been heterogenized on different types of supports, (i) on graphene oxide (GO) through π-stacking interactions between the pyrene group of the bpea-pyrene ligand and the GO and (ii) both on glassy carbon electrodes (GC) and on graphite rods (GR) through oxidative electropolymerization of the pyrene group, which yield stable heterogeneous photoredox catalysts. GO@trans-fac-3- and GR/poly trans-fac-3-modified electrodes were fully characterized by spectroscopic and electrochemical methods. Trans-fac-3 and GO@trans-fac-3 photocatalysts (without a photosensitizer) showed good catalytic efficiency in the photooxidation of alcohols in water under mild conditions and using visible light. Both photocatalysts display high selectivity values (>99%) even for primary alcohols in accordance with the presence of two-electron transfer processes (2e-/2H+). GO@trans-fac-3 keeps intact its homogeneous catalytic properties but shows an enhancement in yields. GO@trans-fac-3 can be easily recycled by filtration and reused for up to five runs without any significant loss of catalytic activity. Graphite rods (GR@trans-fac-3) were also evaluated as heterogeneous photoredox catalysts showing high turnover numbers (TON) and selectivity values.

Near-IR Electrochromic Film with High Optical Contrast and Stability Prepared by Oxidative Electropolymerization of Triphenylamine Modified Terpyridine Platinum(II) Chloride.

Terpyridine (TPY) platinum(II) chloride with a triphenylamine (TPA) group was successfully synthesized. The strong intramolecular Donor(TPA)-Acceptor(TPY) interaction induced the low-energy absorption band, mixing the spin-allowed singlet dπ(Pt)→π*(TPY) metal-to-ligand charge transfer (MLCT) with the chloride ligand-to-metal charge transfer (LMCT) and chloride ligand-to-ligand (TPY) charge transfer (LLCT) transitions, to bathochromically shift to λmax = 449 nm with significant enhancement and broadening effects. Using the cyclic voltammetry method, its oxidative electropolymerization (EP) films on working Pt disk and ITO electrodes were produced with tunable thickness and diffusion controlled redox behavior, which were characterized by the SEM, EDS, FT-IR, and AC impedance methods. Upon applying +1.4 V voltage, the sandwich-type electrochromic device (ECD) with ca. 290 nm thickness of the EP film exhibits a distinct color transformation from red (CIE coordinates: L = 50.75, a = 18.58, b = 5.69) to dark blue (CIE coordinates: L = 45.65, a = -1.35, b = -12.49). Good electrochromic (EC) parameters, such as a large optical contrast (ΔT%) of 78%, quick coloration and bleaching response times of 2.9 s and 1.1 s, high coloration and bleaching efficiencies of 278.0 and 390.5 C-1·cm2, and good cycling stability (maintains 70% of the initial ΔT% value after 3200 voltage switching cycles), were obtained.

A Direct Route to a Polybromothiophene as a Precursor for Functionalized Polythiophene by Electrooxidative Polymerization

A Direct Route to a Polybromothiophene as a Precursor for Functionalized Polythiophene by Electrooxidative Polymerization

Electrogeneration of N-substituted polyaniline micro/nanoparticles with potential for energy storage

In the pursuit to develop functionalized polyaniline (PANI) micro/nanoparticles suitable for electrical charge storage, the electrochemical copolymerization of N-(3-sulfopropyl) aniline (AnPS) and N-(2-hydroxyethyl) aniline (AnEtOH) was performed to generate electroactive N-substituted PANI layers directly deposited onto conductive substrates. A particular attention was focused on the impact of the comonomer's molar ratio and pH of the electrolysis solutions on the morphology and electrochemical properties of PANI electrodeposited layers. Thus, four mixtures of the monomers were subjected to electrochemical polymerization in two electrolyte solutions (1 M H2SO4 and acetate buffer solution, pH 4.5) that led to green, homogeneous copolymer deposition layers on the electrode surface. These provided different structural morphologies, that varied from spherical microparticles generated from solution with slightly acidic pH (4.5) to dense, granular morphological features in the case of the deposition layers electrogenerated from 1 M H2SO4. These were characterized in detail by FT-IR and UV–Vis spectroscopies, which confirmed their proposed chemical structure. The electrooxidative polymerization mechanism of the studied N-substituted aniline monomers was evidenced by spectroelectrochemical studies, which highlighted the influence of the monomer's molar ratio and solutions’ pH on the electrolysis process. Moreover, it was demonstrated that the particle dimensions and distributions can be controlled by the comonomer's molar ratio and electrolysis parameters. Considering that the high specific surface area of the obtained PANI micro/nanoparticles can contribute to a better wettability of the polymer molecules with electrolyte ions and their diffusion, the capacitive behaviour of these PANI films was investigated by cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD). The highest areal specific capacitance, of 5.32 mFcm−2, was obtained for the polymer electrogenerated from 1:1 molar ratio of the two monomers, that distinguished by the related polymers through a better ion diffusion at low scan rates and efficient charge transfer at high scan rates.

Electro-Oxidative Polymerization of Aromatic Monomers without an Electric Power Supply

Electrochemistry is a powerful tool for organic synthesis based on electron transfer-driven reactions at the substrate/electrode interface. The use of electricity for synthetic reactions without the need for hazardous chemical oxidants and reductants is recognized as a green and sustainable approach. We have recently developed a split bipolar electrode (s-BPE) system [1], in which the redox reactions can be driven in a low electrolyte concentration, with batch [2,3] and flow [4] cells. Herein, we report a novel s-BPE system for organic electrosynthesis driven under a streaming potential condition with a pressure flow. As a proof-of-concept study on electrosynthesis without an electric power supply, electrochemical oxidative polymerization of aromatic monomers such as pyrrole successfully yielded the corresponding polymer films on an electrode surface at the upstream, which acted as an anode [5].[1] Shida, N.; Zhou, Y.; Inagi, S. Chem. Res. 2019, 52, 2598-2608.[2] Miyamoto, K.; Nishiyama, H.; Tomita, I.; Inagi, S. ChemElectroChem 2019, 6, 97-100.[3] Shida, N.; Villani, E.; Sanuki, M.; Miyamoto, K.; Gotou, A.; Isogai, I.; Yamauchi, A.; Fuchigami, T.; Tomita, I.; Inagi, S. Electrochemistry, 2021, 89, 476-479.[4] Sakagami, H.; Takenaka, H.; Iwai, S.; Shida, N.; Villani, E.; Gotou, A.; Isogai, T.; Yamauchi, A.; Kishikawa, Y.; Fuchigami, T.; Tomita, I.; Inagi, S. ChemElectroChem, 2022, 9, e202200084[5] Iwai, S.; Suzuki, T.; Sakagami, H. Miyamoto, K.; Chen, Z.; Konishi, M.; Villani, E.; Shida, N.; Tomita, I.; Inagi, S. Commun. Chem., 2022, 5, 66.

Photoactivities of thiophene monomer/polymer transition in gel–based photoelectrochemical assembly: A theoretical/experimental approach

Photoactivities of bithiophene and/or terthiophene monomers and their mixtures were studied before and after being subjected to in situ oxidative electropolymerization in gel electrolyte (GE). Measured band gaps and density functional theory calculations supported the presence of oligomers in conjunction with the expected polymers. More oligomers formed during polymerization of the mixed monomers than with pure monomers. The generated photocurrent from the polymer/oligomer was always greater than that of the monomer. These results support the assumption that increasing π-bond conjugation leads to better e/h formation, and charge separation. The study also shows that the increase of the TerTh percentage in the monomer’s mix increased the generated photocurrent by the existing polymer/oligomer mix in a linear monotonic relationship

Electrochemical synthesis and properties of polyporphyrin films based on 5,10,15,20-tetra(4-pyridyl)porphyrin

Polyporphyrin films were obtained by electrooxidative polymerization of 5,10,15,20-tetra(4-pyridyl)porphyrin which, in turn, was obtained by condensation of pyrrole with pyridine-4-carboxaldehyde. The polymer formation involved the side substituents, with the π-conjugated porphyrin platform being preserved. The obtained polyporphyrin forms an electroconductive coating possessing semiconductor properties with the band gap of 1.76 eV

Strengthening adhesion of polycarbazole films on ITO surface by covalent electrografting of monomer

Strong adhesion of a functional polymer coating to a solid support is a key requirement to achieve its robustness and high performance in different application areas. Herein, a novel carbazole derivative, 9-methyl-9H-carbazole-3,6-diamine (m-Cz-diamine), is synthesized and covalently grafted onto an ITO surface through the diazonium electroreduction method. The functionalization of the ITO surface is confirmed by XPS spectroscopy, water contact angle measurements and cyclic voltammetry analysis, revealing the covalent anchoring of an organic film (m-Cz-ITO). The functionalized ITO surface is then studied for oxidative electropolymerization of m-Cz-diamine and carbazole, showing clear advantages over a bare ITO substrate in terms of polymer film adhesion. The polymer films electrodeposited onto an electrografted ITO surface demonstrate very strong adhesion, as they do not delaminate, either by a scotch tape pulling, storing in air, or immersing under water for two months. On the other hand, the polymer films grown on a bare ITO substrate peel off easily in all the aforementioned stability tests. Therefore, electrografting an organic film onto the ITO surface clearly improves the adhesion of the polymer films on top of it. Moreover, it is interesting to note that the physicochemical properties of the polymer films deposited on the functionalized ITO substrate remain unchanged.

Electrochemistry and Electrochromic Performance of a Metallopolymer Formed by Electropolymerization of a Fe(II) Complex with a Triphenylamine-Hydrazone Ligand.

The complex of Fe(II) ions of general formula [FeL2 ](BF4 )2 with triphenylamine-hydrazone ligand L has been synthesized and characterized. Oxidative electropolymerization of the complex proceeded smoothly on the working electrode producing a homogenous thin film of metallopolymer. The film thickness and morphology of the layer was investigated by microscopy techniques such as scanning electron microscopy and atomic force microscopy, and the composition of the film was confirmed by X-ray photoelectron spectroscopy analysis. It was found that fifty successive oxidation/reduction cycles resulted in a 120 nm thick film on the electrode surface. The metallopolymer was also characterized using cyclic voltammetry and spectroelectrochemical methods. The film was found to change its color from yellow to green-blue, exhibit high change in transmittance of 60 % at 770 nm, and possess good electrochemical stability during 375 cycles of switching of the potential between -0.1 V and +1.5 V, owing to the presence of metal ions that link two ligand molecules resulting in formation of highly cross-linked film. The switching times (coloration and bleaching) were calculated to be 34.2 s and 7.3 s, respectively. Coloration efficiency of the formed film of polymeric complex was found to be 144 cm2 C-1 .

Electrochemical Synthesis, and Electrochromic Properties of Poly(2-(9H-Carbazol-9-yl)acetic acid) Film

A poly(2-(9H-carbazol-9-yl) acetic acid) thin-film was formed on the surface of a platinum (Pt) electrode by oxidative electropolymerization of a new carbazole derivative. Electrochemical polymerization was performed in reaction medium containing monomer and 0.1 M TBABF4 mixture in acetonitrile (ACN) using repeated cycling at a scanning rate of 250 mV. The electrochemical polymerization of 2-(9H-carbazol-9-yl) acetic acid (25mM) was studied using cyclic voltammetry on both Pt and ITO electrodes. The structure of the soluble polymer was elucidated by nuclear magnetic resonance (1H and 13CNMR) and Fourier transform infrared (FTIR) spectroscopy. The weight average molecular weight of poly(2-(9H-carbazol-9-yl) acetic acid) was determined using gel permeation chromatography (GPC) and found to be 130900 g/mol. Characterizations of the resulting polymer were performed by cyclic voltammetry, dry conductivity measurement and scanning electron microscopy (SEM), while the UV-Visible spectroscopy and electrochemical spectroscopic studies indicated that the poly(2-(9H-carbazol-9-yl) acetic acid) film showed a green color in the oxidized state, and high transmittance in the neutral state. Moreover, the poly(2-(9H-carbazol-9-yl) acetic acid) film is soluble in common organic solvents, such as DMSO, THF, NMP, and DMAC. The conductivities of poly(2-(9H-carbazol-9-yl) acetic acid) is about 4.3x 10-2 S/cm.

Oxidative electropolymerization films of a styrene-appending ruthenium complex with highly performed electrochemical, solar photoelectric conversion and photoelectrochemical oxygen reduction properties

Vinyl or styrene-containing ruthenium complexes were previously reported to be reductively electropolymerized, which needed to be carried out under strict deoxygenation conditions. Here, we present the first example of an oxidatively electropolymerized thin film of a styrenyl-containing ruthenium complex, Ru1 under ambient condition. As revealed by UV–visible absorption spectroscopy, emission spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, electrochemical impedance spectroscopy, cyclic voltammetry, and photoelectrochemical measurements, the electropolymerized films, poly(Ru1)n, exhibited good adherence and chemical stability, porous structure, strong photoluminescence, well reversible and surface-controlled RuIII/II redox behavior. More interestingly, at a -0.4 V external bias potential, a significant cathodic photocurrent density of 8.04 μA/cm2 was observed for poly(Ru1)3-modified ITO electrode irradiated by 100 mW•cm−2 white light in an air-equilibrated 0.1 M Na2SO4 aqueous solution. Furthermore, the photo-current polarity could be switched from cathodic to anodic up to a photocurrent density of 9.22 μA/cm2 for poly(Ru1)3-modified ITO electrode as the electron donor of quinhydrone was added under external bias potential-free conditions. More interestingly, poly(Ru1)3 exhibited impressively strong photoelectrochemical oxygen reduction properties with a O2-induced 4.7-fold cathodic photo-current enhancement relative to a N2-saturated electrolyte solution condition. This work offers an efficient way to fabricate highly stabilized Ru(II) complex-based modified electrodes by facile oxidative electropolymerization of the styrenyl-containing ruthenium complex, offering poly(Ru1) films with intriguing applications in electrochemical, photoluminescence, photoelectrochemical O2 reduction and solar photoelectric conversion, molecular switching devices.

Study on Spectro-Electrochemical Behaviour of Thin-Layer Polymer of 3-(9H-Carbazol-9-yl)propanenitrile

A film of electrically active poly(3-(9H-carbazol-9-yl)propanenitrile) was prepared on platinum (Pt) electrode surface by oxidative electro-polymerization of 3-(9H-carbazol-9-yl)propanenitrile monomer. The polymerization reaction was performed in a reaction medium containing monomer, and 0.1 M tetrabutylammonium tetrafluoroborate (TBABF4 ) mixture in acetonitrile (ACN) using repeated cycling at a scanning rate of 250 mV. Electrochemical polymerization of carbazole (Cz) and 3-(9H-carbazol-9-yl)propanenitrile (25 mM) were studied with cyclic voltammetry on both Pt and ITO electrodes. The structure of the poly(3-(9H-carbazol-9-yl)propanenitrile) was elucidated by nuclear magnetic resonance (1H and 13C NMR) and Fourier transform infrared (FTIR) spectroscopy. The weight average molecular weight (Mw) of the electrochemically synthesized poly(3-(9H-carbazol-9-yl)propanenitrile) was determined using gel permeation chromatography (GPC), where it was found that the Mw of the polymer is equal to 37900 g/mol. The polymer was characterized using dry conductivity measurement, scanning electron microscopy (SEM) and UV-Vis spectroscopy, while the spectro-electrochemical studies indicated that poly(3-(9H-carbazol-9-yl)propanenitrile) films revealed a green color in the oxidized state and a high transmittance in the neutral state. Moreover the poly(3-(9H-carbazol-9-yl)propanenitrile) film is soluble in common organic solvents, like DMSO, THF, NMP and DMAC. The conductivity of poly(3-(9H-carbazol-9-yl)propanenitrile) was found to be 1.62x10-4 S/cm.

Pale yellow-to-dark blue electrochromic film produced by oxidation electropolymerization of a triphenylamine derivative with an enhanced electron-withdrawing group

The triphenylamine derivative with a terpyridine-like unit, {4-[p-(N,N-diphenylamino)-phenyl]-2,6-di(pyrazin-2-yl)pyridine}, and its doubly N-methylated salt have been successfully synthesized and characterized. The salt with much enhanced intramolecular D-A interaction shows a remarkable bathochromical shift of its absorption bands and a fluorescence quenching effect. And its oxidative electropolymerization film with tunable thickness and non-diffusion controlled redox behavior has also been obtained by cyclic voltammetry on the working ITO electrode. The film possesses an independent dual-wavelength response in visible (400–850 nm) and near-infrared (850–2100 nm) spectral regions under different voltages. The low-voltage-controlled electrochromism displays significant color change from pale yellow to dark blue (ΔT% = 78%) with fast response time (6 s for the coloration step and 3 s for the bleaching step), high coloration and bleaching efficiencies (363.7 and 238.5 C-1·cm2) at λmax = 730 nm between −0.2 and + 1.2 V.

Electrochemical Comparison on New (Z)-5-(Azulen-1-Ylmethylene)-2-Thioxo-Thiazolidin-4-Ones

Three (Z)-5-(azulen-1-ylmethylene)-2-thioxo-thiazolidin-4-ones are electrochemically characterized by cyclic voltammetry, differential pulse voltammetry, and rotating disk electrode voltammetry. The electrochemical investigations revealed that the redox potential is influenced by the number and position of the alkyl groups, and the possible oxidation mechanism is proposed. These compounds, after their immobilization on glassy carbon electrodes during oxidative electropolymerization, were examined as complexing ligands for heavy metal ions from aqueous solutions through adsorptive stripping voltammetry.

A dual-wavelength electrochromic film based on a Pt(ii) complex for optical modulation at telecommunication wavelengths and dark solid-state display devices

The film prepared by oxidative electropolymerization of a cyclometalated Pt(ii) phenylacetylide shows the independent optical modulation at 1520 nm under +1.0 V, and the long-term electrochromic behaviour at 773 nm between −0.5 and +1.6 V.

Electrooxidative generation of polymer films from rigid tricarbazole monomers.

In this report, syntheses and subsequent electropolymerization of a series of five rigid tricarbazole monomers are described. The monomers involve three planar triphenylene-cored tricarbazole-benzenes (with the carbazole units connected via their a- or b-planes) and two triptycene-cored derivatives. Oxidative electropolymerization of these monomers leads to a continuous growth of smooth and freestanding thin films. Moreover, one type of polymer film, based on a poly-a-tricarbazole network (paTC), shows the occurrence of intrinsic microporosity properties, with a specific BET surface area of 260 m2 g−1.

Electropolymerization of [2 × 2] grid-type cobalt(II) complex with thiophene substituted dihydrazone ligand

The grid-type complex [Co4(L1-2H)4] containing dihydrazone ligand decorated with thiophene rings has been prepared. The complex undergoes oxidative electropolymerization onto ITO electrode to form purple thin film. The morphology of polymer film on ITO electrode was analyzed by SEM and AFM imagining. It was found that polymer obtained by electropolymerization method is homogenous and uniform. The obtained thin film exhibits color transition from purple via violet to blue due to the stepwise reduction of poly-[CoII4(L1-2H)4] into poly-[CoII2CoI2(L1-2H)4]2− and poly-[CoI4(L1-2H)4]4−. Its electrochromic properties such as long-term stability coloration efficiency and switching times have been investigated.