Polyazulene Films Research Articles

Effect of Oxidants on Properties of Electroactive Ultrathin Polyazulene Films Synthesized by Vapor Phase Polymerization at Atmospheric Pressure.

A non-benzenoid aromatic hydrocarbon azulene, naturally found in plants and mushrooms, is known for its derivatives applications in medicines. However, the processability of its chemically synthesized high-capacitance polymer is constrained by the sparingly soluble nature of its polymeric form. Oxidative chemical synthesis on a desirable substrate overcomes this difficulty. In this report, polyazulene (PAz) thin films are synthesized by vapor phase polymerization at atmospheric pressure using oxidants, such as CuCl2, CuBr2, FeCl3, and FeTOS. The effect of oxidants on morphologies of PAz films is studied using atomic force microscopy and microscope imaging. Each oxidant produced distinct microstructures in the films. The films synthesized using Cu(II) salts showed organized and knitted structures, whereas Fe(III) salts formed casted sheet-like disordered arrangements. The films synthesized using CuCl2 created uniform porous film assemblies. The pre-peak formations and their splitting observed in the cyclic voltammograms revealed phase segregations in the films. Oxidant-dependent structural and chemical differences such as charge carrier formation, doping levels, and polymer chain length in the PAz films are studied by using UV-Vis and FTIR spectroscopy. The results indicated that 240 and 180 mM are the optimum concentration of CuCl2 to produce high capacitance and well-organized single- and triple-layered PAz films, respectively.

Fabrication of electroactive multi-layered polyazulene thin films by atmospheric pressure-vapor phase polymerization

Thin films of polyazulene (PAz) are produced by using an optimized atmospheric pressure–vapor phase polymerization (AP-VPP) method. Method optimization is carried out by studying the effect of cell temperature, substrate temperature, polymerization time, and washing-solvent on film properties like optical bandgap, sheet resistance, surface roughness, and % transmittance (%T). Multi-layered PAz films were produced by layer-by-layer engineering. The effects of thin, electroactive multiple layers on film properties are investigated. UV–Vis, IR, and Raman analysis are utilized to understand the extended conjugation length and nature of the charge carriers. The spectroscopic data revealed the anomalous behaviour of PAz at a high level of doping. The proportion and amount of quinoid conformation is discussed. The addition of layers changes the transport of ions across the electroactive PAz films, which is studied using cyclic voltammetry at various scan rates. AFM and SEM images reveal a change in structural properties which is further correlated with a deviation of capacitance values at elevated scan rate. Comparison with earlier reported literature on electrochemically and chemically synthesized PAz is also provided. The conductivity, transparency and high capacitance show a promising application of AP-VPP PAz in various fields.

Electropolymerized polyazulene as active material in flexible supercapacitors

Abstract We report the capacitive behavior of electrochemically polymerized polyazulene films in different ionic liquids. The ionic liquids in this study represent conventional imidazolium based ionic liquids with tetrafluoroborate and bis(trifluoromethylsulfonyl)imide anions as well as an unconventional choline based ionic liquid. The effect of different ionic liquids on the polymerization and capacitive performance of polyazulene films is demonstrated by cyclic voltammetry and electrochemical impedance spectroscopy in a 3-electrode cell configuration. The films exhibit the highest capacitances in the lowest viscosity ionic liquid (92 mF cm −2 ), while synthesis in high viscosity ionic liquid shortens the conjugation length and results in lower electroactivity (25 mF cm −2 ). The obtained films also show good cycling stabilities retaining over 90% of their initial capacitance over 1200 p-doping cycles. We also demonstrate, for the first time, flexible polyazulene supercapacitors of symmetric and asymmetric configurations using the choline based ionic liquid as electrolyte. In asymmetric configuration, capacitance of 55 mF (27 mF cm −2 ) with an equivalent series resistance of 19 Ω is obtained at operating voltage of 1.5 V. Upon increasing the operating voltage up to 2.4 V, the capacitance increases to 72 mF (36 mF cm −2 ).

Chemically Modified Electrodes Based on 5-(Azulen-1-yl)methylene)-2-thioxothiazolidin-4-one

This work is devoted to the electrochemical characterization of a new azulene compound (Z)-5-[(azulen-1-yl)methylene]-2-thioxothiazolidin-4-one (L) by cyclic, differential pulse, and rotating disk electrode voltammetries (CV, DPV and RDE, respectively). The redox processes in acetonitrile solutions are established, analyzed and some of them have been assigned to the particular functional groups at which they take place. The influence of L concentration, scan rate and scan domain in CV, and rotation rate in RDE, have been studied. Formation of a polyazulene film has been observed in millimolar solutions of L in 0.1 mol·L−1 tetrabutylammonium perchlorate in acetonitrile by successive scans in the domain of the first anodic process or by controlled potential electrolysis. Evidence for the films was obtained by electrochemistry through transfer of the modified electrodes in ferrocene solutions. The best conditions for the film synthesis (electropolymerization potential and charge) have been established. The SEM images allowed the characterization of the polyL films morphology under the conditions established for film deposition.

Influence of hydrophobization of the polyazulene ion-to-electron transducer on the potential stability of calcium-selective solid-contact electrodes

We introduce here electrosynthesized polyazulene (PAz) as a new ion-to-electron transducer material in solid-contact ion-selective electrodes (SC-ISEs). It is shown that the neutral form of PAz possesses high hydrophobicity (water contact angle: 126±14°) due to its aromatic carbon structure. This makes PAz attractive as a solid-contact (SC) material in SC-ISEs in combination with its high redox capacitance which is three times higher than for PEDOT-PSS. We have studied the electrochemical stability of PAz in direct contact with aqueous electrolyte solutions and applied it as the SC layer buried under a calcium-selective plasticized poly(vinyl chloride) ion-selective membrane (ISM). It is demonstrated that the hydrophobization of the PAz solid-contact at E≤0.2V significantly improved the potential stability of the calcium-selective SC-ISEs which showed a potential drift of only 0.5mVh−1 when the ISMs were for the first time contacted with 0.1M CaCl2 for 24h. Simultaneous determination of the potential stability and the water uptake with the FTIR-ATR spectroscopy could not clearly prove the correlation between low water content at the PAz/substrate interface and the good potential stability obtained with the pre-hydrophobized SC-ISEs. This is due to the relatively uneven surface morphology of the PAz film making the evanescent standing wave of the IR beam to sense water not only in the PAz transducer layer, but also in the ISM. Hence, it is not possible to distinguish between the distribution of water in the ISM and the PAz solid-contact layer. The new SC material presented here was also characterized with cyclic voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy.

Capacitance properties of electrochemically deposited polyazulene films

Polyazulene films formed by electrochemical oxidation of azulene have been studied as active components in electrochemical capacitors. The film shows reversible electrochemical behavior in the positive potential range and exhibits p-doping properties. The influence of film formation conditions on the films electrochemical properties has been investigated. A strong effect of solvent on the polyazulene deposition has been observed. The highest yield of film deposition was found for dichloromethane. Polyazulene films also exhibit stable voltammetric properties in aprotic solvents. The voltammetric response of the film is affected by the size of the anion of the supporting electrolyte. In solutions containing tetra(alkyl)ammonium perchlorates, tetrafluoroborates or hexafluorophosphates, reversible oxidation of polyazulene is obtained. In the presence of large tetra(phenyl)borate anions, polyazulene is irreversibly oxidized upon electrochemical oxidation. The capacitance properties of these materials have been investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The polyazulene film displays a relatively high specific capacitance close to 400 F g −1. Such high value of C s locates this material among very good polymeric redox pseudo-capacitors.

The Nature of the Charge Carriers in Polyazulene as Studied by in Situ Electron Spin Resonance−UV−Visible−Near-Infrared Spectroscopy

In situ spectroelectrochemistry is of high importance for the characterization of doping reactions in pi-conjugated polymers. In this paper we present the results of simultaneous ESR and UV-vis-NIR measurements performed in situ during electrochemical p- and n-doping of polyazulene (PAz). In previous studies on p-doping of PAz the assignment of the optical absorption bands to specific charge carriers have been somewhat controversial, therefore the aim of this study is to clarify the nature of the doping-induced charge carriers and their corresponding optical absorption bands by in situ ESR-UV-vis-NIR spectroelectrochemistry. PAz was polymerized in two different potential ranges in order to obtain films with different structures and morphologies. On the basis of our spectroelectrochemical results we propose that polarons and polaron pairs are formed during p-doping in the two different types of PAz films electrodeposited on ITO. For studying n-doping of PAz, a Pt electrode was used. The ESR signal first decreased in intensity at low doping levels and then increased in intensity at higher doping levels pointing to the formation of new paramagnetic species. At high negative potentials there occurred an additional line broadening of the ESR signal indicating the existence of rather localized negative charge carriers.

Spectroelectrochemical study of the redox reactions of polyazulene on aluminum substrates

Abstract Polyazulene (PAz) films have been electrochemically synthesized on aluminum substrates. Both p - and n -doping of the formed PAz films have been studied on Al and Pt substrates with cyclic voltammetry (CV), in situ FTIR with Attenuated Total Reflectance mode (FTIR–ATR), and in situ UV–vis. During p -doping on both substrates the IR spectra show an appearance of infrared active vibration bands (IRAV) in the wavenumber region 1600–800 cm −1 . The IRAV bands increase with increased charging level and appear at the similar wavenumbers regardless of the substrate. In the case of n -doping the spectroelectrochemical response was dependent on the substrate. PAz on Pt showed a reversible n -doping behavior, this could be confirmed with in situ FTIR–ATR and in situ UV–vis. PAz on Al did not show a reversible n -doping although the film did undergo certain potential induced structural changes during reduction.

Low potential electrosyntheses of high quality freestanding polyazulene films

High quality freestanding polyazulene (PAz) films were synthesized electrochemically by direct anodic oxidation of azulene (Az) in pure boron trifluoride diethyl etherate (BFEE). The oxidation potential of Az in this medium was measured to be only 0.75 V vs. SCE. PAz films obtained from BFEE showed good electrochemical behavior with conductivity of 2.2 S cm − 1 , which indicated that BFEE was a good medium for the electrosyntheses of PAz films. Structural studies implied that the Az units remained intact in the isolated 1,3-polyazulene. As-formed PAz films were insoluble in common organic solvents. To the best of our knowledge, this is the first report on the electrosyntheses of freestanding PAz films in BFEE.

Raman and in Situ FTIR-ATR Characterization of Polyazulene Films and Its Derivate

Polymers from azulene (A) and 2-[(E)-2-azulen-1-ylvinyl]thiophene (B) electrochemically synthesized are materials with a broad absorbance in the UV-vis spectral region. An experimental approach to correlate the Raman and in situ FTIR spectra from azulene based polymers according to the effective conjugation coordinate theory (ECC) is presented. Film characterization was made by Raman and Fourier transform infrared attenuated total reflectance, FTIR-ATR spectroscopy. Throughout the whole work A was used as a model compound. The polymers were synthesized at different polymerization potentials in order to create different structures. Polyazulene showed a divergent Raman response upon change in excitation wavelength, lambda(exc)= 514 nm and lambda(exc)= 780 nm, in comparison to common conducting polymers. The FTIR-ATR measurements were made during charging-discharging of the polymers. The IR spectra of the conducting state show new doping induced infrared active vibrations (IRAV) in the region between 1600 and 700 cm(-1) and a broad electronic absorption in the high energy range (4000-8000 cm(-1)). Two different structures of the polymer from B are formed, and both follow the trends for conducting polymers upon charging.

Electrochemistry of Conductive Polymers: XXII. Electrochemical and Spectroelectrochemical Studies of Polyazulene Growth and Its Characterization

Electrochemical growth of the polyazulene film and its electrochemical and spectroscopic properties were studied at platinum electrodes in acetonitrile by ac impedance and in situ spectroelectrochemical techniques. During polymer growth from the acetonitrile solution containing a millimolar concentration of azulene with 0.1 M tetra‐n‐butylammonium perchlorate as a supporting electrolyte, absorption bands were observed at 380, 480, and 680 nm. These bands were assigned to arise from neutral oligomers, their first oxidation products, and their second oxidation products, respectively. When the polymer film was oxidized in acetonitrile after the polymer is fully grown, absorption bands were red shifted significantly to 580 and around 800 nm, respectively, suggesting that the absorption bands are dependent on the chain lengths.

Electrochemical Study on Charge‐Discharge Performance of Lithium/Polyazulene Battery

Electrodeposited polyazulene (PAz) films show high electroactivity and fast redox switching behavior when polymerized under suitable conditions. Such PAz films are more electroactive than electrodeposited polypyrrole or polyaniline and were successfully applied in a rechargeable lithium battery. We determined suitable polymerization conditions so as to obtain an electroactive PAz film possessing the highest charge‐storing ability and fastest electrode processes. Specifically, the electrochemical kinetics (anion doping‐undoping process) of PAz films was investigated by varying the polymerizing current density and formation charge. Charge capacity showed a maximum value when polymerized at 1.4 mA cm−2by passage of 5C cm−2. Cyclic voltammograms coupled with scanning electrons microscope observation of PAz films evidenced that a highly electroactive PAz film can be prepared at 1.4 mA cm−2. The charge‐discharge property and cyclability of batteries were studied. batteries showed fairly high and flat discharge voltage (ca. 3.2V), while maintaining 100% coulombic efficiency when charging by ca. 45% of doping level (per unit cathode weight). The battery performed best when PAz film was formed at 1.4 mA cm−2 by passage of 5C cm−2.

Surface plasmon study of electrochemically prepared polymers: Polyazulene

The work reported here shows that by using a modified gold working electrode, the surface plasmon technique can successfully be used to obtain information on the optical constants and the film thickness of electropolymerized films. Polyazulene films deposited at three different surface charge densities are investigated in the oxidized and corresponding reduced forms. Our result shows that the refractive index, and hence the dielectric constant at 632 nm, is complex, the imaginary part being larger for the oxidized form compared to that for the corresponding reduced form. Thickness determination shows that its relationship with the amount of charge is qualitatively similar to that reported for polypyrrole. The film thickness measurement reveals a shrinkage in going from the oxidized to the reduced form as the counter anions are removed. Our study, therefore, shows that the surface plasmon technique can be used to probe ionic processes.

Application of Electrochemically Formed Polyazulene to Rechargeable Lithium Battery

An electrochemically formed polyazulene(PAz), one of the electroconductive polycyclic hydrocarbons, was studied for its electrochemical properties in order to examine the possibility of utilizing it as a cathode active material of rechargeable lithium battery. The electrode kinetics of PAz film electrode, especially the anion doping‐undoping process, were investigated mainly with cyclic voltammetry and FFT impedance method. The cyclic voltammetric results of PAz film showed a highly reversible redox process. Cole‐Cole plots for PAz electrode obtained by impedance measurement as a function of doping potential were also found to offer an indication that PAz can be an excellent battery material. The charging‐discharging property, and the cyclability of a battery were then studied as a function of the film thickness of PAz cathode. The charging‐discharging behavior of was also compared with those of and batteries, which had been examined earlier. When compared with or batteries, a battery showed fairly high and constant discharge voltage (ca. 3.2V), while keeping 100% of coulombic yield. Inspection by SEM showed that the surface condition of PAz film greatly resembled that of polypyrrole, however, a 10 C cm−2 PAz film was prepared with thicker than polypyrrole formed with the same amount of charge of 10 C cm−2.

Electrical and optical properties of fused ring polymers

The electrochemical, magnetic and optical properties of electrochemically prepared polyazulene and polyindene have been studied. The neutral polyazulene film shows an extraordinary large ESR spin density and two optical absorption peaks corresponding to the interband transition. In a cyclic voltammogram of polyazulene, two pairs of oxidation and reduction peaks have been observed, suggesting two-stages doping process. In the in situ ESR and optical measurements during electrochemical doping, associated with these redox peaks, the spin density changes anomalously and new optical absorption peaks characteristic to each doping stage appear successively. These results are explained tentatively by proposing a “dual band structure” as an electronic energy band scheme of polyazulene.