Polyacene Quinone Research Articles

Decoration of conjugated polyacene quinone radical (PAQR) with Fe3O4 nanospheres achieving improved impedance matching and electromagnetic wave absorption

Conjugated polymers have exhibited great potential to reform traditional electromagnetic wave absorbers owing to their advantages in tailorable electrical properties, lightweight, good processability, high environment resistance, and so on. In this work, conjugated polymer of polyacene quinone radical (PAQR) with unique nomadic polarization behavior was prepared by a solid-state polymerization process and subsequently decorated with Fe3O4 nanospheres through a solvothermal method to obtain PAQR/Fe3O4 nanocomposites. Electromagnetic wave absorbing properties of the polymer-based nanocomposites were thoroughly discussed. It was found that PAQR decorated with Fe3O4 in moderation exhibited excellent wave absorbing abilities with absorbing bandwidth of 4.8 GHz and reflection loss exceeding - 40 dB at a thin thickness around only 1.5 mm. The wave absorbing mechanisms were not only attributed to polarization loss and conduction loss of conjugated macromolecules, but also related to that the decoration of Fe3O4 significantly improved the magnetic loss abilities and impedance matching for the nanocomposites. This work firstly studied the electromagnetic properties of PAQR-based composites in GHz bands and proposed a powerful support for the development of conjugated polymer wave absorbing materials.

Spin filtering and negative differential resistance in PAQR-ZGNR junctions

The spin transport of a Polyacene quinone radical (PAQR) molecule sandwiched between two ferromagnetic ZGNR electrodes with an even width number of 6 is studied employing the nonequilibrium Green's function method combined with the density functional theory (NEGF-DFT). Lateral symmetry mismatch of wave functions between PAQR and ZGNR may suppress all the transport channels except only one spin-down channel near the chemical potential in the linear regime. A half-metallic behavior with perfect spin filtering efficiency and strong negative differential resistance is expected. Under high bias voltage, the spin filtering efficiency changes from −100% to 90% when other transport channel is involved. Applying an external gate voltage, we can modulate greatly the conductance of the junction. These unique features are insensitive to the length of PAQR chain and suggest great application prospect for PAQR-ZGNR molecule devices.

Synthesis and characterization of three different structures of polyacene quinone radical polymers

Three types of polyacene quinone radical (PAQR) polymers were synthesized by the step-growth polymerization of naphthalene, anthracene, or anthraquinone reacting with pyromellitic dianhydride via solution polymerization under a temperature gradient. Zinc chloride was used as the catalyst, and nitrobenzene was the solvent. The different structures of PAQR polymers were analyzed by infrared, X-ray diffraction, and scanning electron microscopy. The thermal properties of PAQR polymers were described by thermal gravimetric analysis, and the electrical performances were investigated by a precision LCR meter and a digital high insulation meter.

Hollow PAQR nanostructure and its smart electrorheological activity

Hollow polyacene quinone radical (PAQR) submicrospheres are synthesized by a modified solvothermal method. The morphology and structure of the hollow PAQR submicrospheres were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and Haake rotational rheometer, respectively. Meanwhile, both the size and the shell thickness of PAQR hollow submicrospheres could be adjusted by changing the amount of surfactant-sodium dodecyl sulfate (SDS). When PAQR hollow submicrospheres are used as the electrorheological (ER) dispersed materials, good ER effect is achieved. Furthermore, the hollow structure is beneficial to improve the anti-sedimentation property for ER application.

Preparation and Characterization of PAQR Polymers by Different Methods

Polyacene quinone radical (PAQR) polymers were formed by different methods, using anthraquinone and pyromellitic anhydride with aromatic acids through the solvothermal method and solid phase melted polymerization. High temperature was also applied to increase the polymerization degrees and exclude the oligomer that can not be excluded during the purification process. The different structures of PAQR polymers were analyzed by XRD, Raman, XPS, and Element Analyzer. The properties of PAQR polymers were investigated through TG and VNA.

Ab initio study of electronic structure, quantum transport and optical absorption properties of polyacene quinone radical polymers

Semiempirical quantum mechanical calculations have been implemented to study the molecular structure, electronic structure, optical properties of polyacene quinone radical polymers, and the quantum transport properties are also been calculated through combination of the numerical atomic orbitals basis set method based on density functional theory with the non-equilibrium Green's function formalism. The polyacene quinone radical polymers exhibit similar elastic modulus to the carbon nanotubes. The electronic molecular orbitals and energy bands of polyacene quinone radical polymers show insulator features, with the great conjugated bonds formed in polymer molecules resulting in extreme high polarization and dielectric constants, and the Fermi energy and band-gaps of ultraviolet range are static with the variation of polymerization degree. The aluminum electrodes with crystallographic (001) surfaces have been used in the electronic transport calculations, which indicate the quantum conductance spectrum changes with the varied strain and polymerization degree, however appears no explicit change, representing large open-gap feature of insulators. Ultraviolet-visible absorption spectra show a few characteristic peaks, the positions and number of which varying with polymerization degree, predicting that polyacene quinone radical polymers, as high dielectric functional materials, could be applied to ultraviolet optoelectronic nanoscale quantum devices.

Synthesis of polyacene quinone radical polymers with controllable conductivity and their smart electrorheological behavior

Polyacene quinone radical (PAQR) polymers were synthesized by the step-growth condensation of aromatic hydrocarbon derivatives reacting with pyromellitic anhydride via a solvothermal method. The morphology and structures of PAQRs with varied polymerization processes were confirmed by the analysis of X-ray, IR, SEM and TG measurement. The effects of different aromatic hydrocarbons on the synthesis and morphology of PAQR polymers were investigated and then utilized as an electrorheological (ER) material by dispersion in silicone oil. The ER performances are investigated as a function of electric field strength by using a rheometer and the relationship between the conductivity and electrorheological (ER) properties of different polyacene quinone radical (PAQR) polymers were discussed.

Dielectric Studies on the Heterogeneity and Interfacial Property of Composites Made of Polyacene Quinone Radical Polymers and Sulfonated Polyurethanes

Sulfonated polyurethane (PUI, matrix) is synthesized and composited with polyacene quinone radical polymers (PAQRs, filler). The polarization mechanism of these polymers and composites were investigated in terms of their frequency, temperature, and filler-concentration-dependent dielectric properties. We found that PUI/PAQR composites have a high permittivity, which is attributed to the filler-matrix interfacial polarization and the contact effect. The PAQR-concentration-dependent permittivity of different PUI/PAQR composites reveals a percolation threshold at 20-30 wt % with scaling exponents that indicate the intercluster polarization. The frequency dependence of dielectric response is well-fitted by using the Debye and Cole-Cole functions on the basis of the structural diagrams and equivalent circuit, leading to a detailed evaluation on heterogeneous structures of different PUI/PAQR composites.

Synthesis of Polyacene Quinone Radical Polymers by Solvothermal Method

In this paper Polyacene quinone radical (PAQR) polymers were synthesized by the step-growth condensation of aromatic hydrocarbon derivatives reacting with pyromellitic anhydirde via a solvothermal method at 180°C for 2 h, using zinc chloride as catalyst and cyclohexane as solvent. The effects of solvents and different aromatic hydrocarbons on the synthesis and morphology of PAQR polymers were investigated.

Synthesis and characterization of polyacene quinone radical polymers with high-dielectric constant

Polyacene quinone radical polymers (PAQRs) and their hydroxyl- or alkoxyl-modified derivates (HO-PAQR and RO-PAQR) were synthesized through the solid-state heating, the solution polymerization, and the improved process (pre-polymerization before solid-state heating). PAQRs synthesized by the improved process provided the higher yields than those from the other two methods. The high-dielectric constants were achieved for the PAQRs from the solid state and the improved process, due to the high polarization resulted from the existence of large amount of polar domains, which were the aggregation of the conjugated ladder-structured macromolecules with extended regions of associated π-orbital. The HO-PAQRs or RO-PAQRs showed good blending or solving features in polymer or solvent, but they were of low dielectric constants for the groups of hydroxyl and alkoxyl destroyed the planar conjugation of the associated π-orbital, and provided the steric hindrance to the formation of regular stacks of the conjugated macromolecules, which could produce huge polarization. The molecular and the aggregated structures of PAQRs with varied chemical modifications and from varied polymerization processes were confirmed by the analysis of X-ray, IR, TG, TEM and the dielectric measurement.

Effect of barrier mechanisms of polarization on the determination of the parameters of polyacene quinone semi-electrics

Effect of barrier mechanisms of polarization on the determination of the parameters of polyacene quinone semi-electrics

Temperature dependence for the frequency position of the low-frequency dielectric dispersion in the polyacenequinone spectrum and quantum measurements

The current state of the art in the physics of mesoscopic and strongly correlated electron systems [1] necessitates an appeal to the conceptual tenets of quantum mechanics [2, 3]. We associate the low-frequency (LF) dispersion region in the dielectric spectrum of polyacenequinone (PAQ) synthesized by polycondensation of pyrene with pyromellitic dianhydride at 300 ° C with the phenomenon of quantum coherence in a system of donor‐acceptor (D‐A) complexes. We imply a system of atmospheric oxygen intercalated into graphite-like fragments of the surface-layer structure of PAQ granules and two-dimensional polyaromatic layers [4]. In the present paper, the temperature behavior of the LF maximum in the frequency dependence of the tangent δ ( ν ) of the dielectric-loss angle δ ( ν ) is interpreted on the basis of a scheme of quantum measurements that was recently proposed [3]. For definiteness, we assume that the intercalated oxygen interacts with the π -conjugate system of only one of the adjacent polyaromatic layers. The problem of possible elementary mechanisms of the relaxation polarization is beyond the scope of the present discussion. In the temperature dependence of the position ν m LF

Electrical properties of polymer composties: conducting polymer-polyacene quinone radical polymer

Unique electrical properties are observed in conducting polymer such as poly(3-alkylthiophene) containing various types of polyacene quinone radical polymers (PAQR) such as PMA+Py. Electrical conductivity and its temperature dependence are strongly dependent on concentration of PAQR. Dependences of dielectric properties of the polymer composite on concentration of PAQR and temperature are also anomalous. The results are discussed in terms of electronic band schemes of of both polymers.

Electrical and magnetic properties of new polyacene quinone radical co-polymers synthesized by condensation

We have synthesized several new polyacene quinone radical co-polymers first by condensation and experimentally found a kink at about 1.1 (kbar) on plots of log d. c. conductivity versus the square root of external pressure in a range from 0.1 to 10 (kbar); a possibility of application of Mott's T 1 4 -law to higher temperature region (290–400K); and analogue trends of change between d.c. conductivity and spin concentration, g factor and peak-to-peak linewidth with mole fraction of 4, 4' - (hexafluoroisopropylidene) - diphthalic anhydride (HFDA) introduced. Here, we have given the reasonable explaination of these experimental results.

Effect of temperature and high pressure on conductive behaviour of polyacene quinone radical polymers

We measured the d.c. conductivity of two polymers of polyacene quinone radical type as a function of pressure at various temperatures and found that there is a kink at about 2.5 kbar on plots of log conductivity versus the square root of applied pressures in range from 0.6 to 10 kbar, and that d.c. conductivity-temperature curves, even at higher temperature region (300–400 K) also obey the Mott's T 1 4 -law. In the present paper, we have given the possible interpretation of these experimental results.

The electrical properties of amorphous polymers described by a modified variable-range hopping model

The d.c. conductivity σ dc and the thermopower S of a number of polyacene quinone radical polymers obey the relationship σ dc = σ o exp (− T o / T) 1 3 and S/T = a+bT − 1 3 , typical for two-dimensional variable-range hopping. The results can be explained by Mott's model modified, however, by allowing for a linearly varying density of states near the Fermi level, and by taking into account the form of the wave function of the localized states. Special attention is paid to the prefactor σ o which contains important hopping parameters, such as a frequency factor ν o, usually assumed to be not higher than a typical phonon frequency (∼ 10 13 s −1). The original calculation of Miller and Abrahams (MA) of the hopping rate, however, gives ν o values ranging from 10 16 to 10 21 s −1. For the PAQR polymers reasonable estimates of the parameters are obtained when using MA expressions adapted for two-dimensional systems.

IV. Two-dimensional variable-range hopping in planar conjugated macromolecules

Abstract Electrical conductivity, thermopower and Hall effect measurements have been made on a series of polyacene quinone radical (PAQR) polymers as a function of temperature. The PAQR polymers, prepared by condensing pyrene with three different acidic compounds, are highty conjugated and show fairly high conductivities (in the range 10−4-10−3 Ω−1 cm−1 at room temperature). The thermopower is positive and increases slightly with increasing temperature. The Hall coefficient, measured on one sample, is negative and decreases with temperature; the Hall mobility is less activated than the conductivity and is of the order of 3 × 10−2 cm2 V−1 s−1 at room temperature. In order to alter the electrical properties by doping, the PAQR polymers were treated with iodine. This results in an increase of the conductivity, a sign reversal of the thermopower and a lowering of the Hall mobility. The conductivity and thermopower data seem to be explained in their general features by the two-dimensional variable-range hoppin...

Reversal of the usual electric field effect on the nomadic polarization in polymeric solids

Microwave measurements at 9.9 GHz on polyacene quinone radical copolymers are reported, which confirm the prediction previously presented in the literature, that at a sufficiently high frequency, the usual DC or low-frequency electric field effect observed for materials exhibiting electronic nomadic polarizability will reverse to give an increasing permittivity with increasing field strength. Microwave measurements of this effect will be of use for other organic conducting materials, especially those of possible biological interest.

The charge storage and other electrical properties of a series of polyacene quinone radical polymers

A series of polyacene quinone radical polymers were made. The chemical analysis showed that the severe reaction conditions favored the Scholl (elimination of H2 and H2O) over the Friedel–Crafts reaction. Electron paramagnetic resonance spectra confirmed the presence of a biradical. Conductivity measurements in the ohmic and space charge limited regions showed that large π systems existed and that carrier traps were shallow. The π system structure and absence of quinone structure was confirmed by ir spectrometry which also showed the optical absorption edge to be 0.8 eV. Charge was injected into the polymers forming electrets and thermally stimulated current emission spectra confirmed a shallow trap depth (∼0.4 eV). It is postulated that thermal excitation to a triplet state produces the biradical and conduction is by hopping between adjacent π systems and charge storage is associated with the extensive π systems.

Temperature dependence of hopping transport in polymeric semiconductors

We report the results of measurement and analysis of the electrical conductivity of two synthetic highly purified copolymers of the polyacene quinone radical (PAQR) type. The dc conductivity was examined as a function of temperature and pressure. The conductivity-pressure relation is observed to go as log σ versus P 1 2 . The conductivities under moderate pressure (400–5000 atm) show linear relationships on log σ versus T − 1 4 plots in the temperature range 70 K < T < 300 K. The possible interpretations as variable range hopping or as nearest neighbour hopping with distributions of activation energies are discussed.