Doped Polyacetylene Research Articles

Metathesis cyclopolymerization of substituted 1,6‐heptadiyne and dual conductivity of doped polyacetylene bearing branched triazole pendants

ABSTRACTThe branched triazole group is synthesized by click chemistry via a controlled approach of slow addition of AB2 compound to a B2 core, and used as the substituent for 1,6‐heptadiyne monomer. Metathesis cyclopolymerization of monomer is performed well in dichloromethane without the weakly coordinating additive, indicating that the branched triazole itself can stabilize the living propagating chain, to generate branched triazole pendant‐contained polyacetylene with trans‐double bonds and five‐membered ring repeating units along the conjugated backbone. The LiTFSI doped polyacetylenes display ionic conductivities of 2.5–1.8 × 10−6 S cm−1; by further doping with iodine, polyacetylenes show the improved ionic and electronic conductivities of 1.3 × 10−5 and 2.1 × 10−7 S cm−1 at 30 °C, respectively. Therefore, these doped polyacetylenes may act as the new electrolyte materials. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 485–494

Electrical and optical properties of doped helical polyacetylene graphite films in terahertz frequency range

We report on electrical and optical characteristics such as power absorption, index of refraction, and conductivity of new form of the model conjugated polymer–polyacetylene (PA)–helical PA graphite films (h-PA) in the 0.1–2.5THz spectral range. The results were obtained using the transmission THz time-domain spectroscopy. The frequency dependencies of the electrical and optical characteristics can be reasonably well fitted by the Drude model, which gives a plasma frequency of about ∼124THz and a charge carrier scattering time ∼30fs, which is less by an order of magnitude than that of crystalline materials. The obtained results demonstrate that doped h-PA graphite films retain metallic behavior in the THz spectral range even at ambient conditions contrary to conventional doped PA films.

Micropunching Lithography for Generating Micro- and Submicron-patterns on Polymer Substrates

Conducting polymers have attracted great attention since the discovery of high conductivity in doped polyacetylene in 1977(1). They offer the advantages of low weight, easy tailoring of properties and a wide spectrum of applications(2,3). Due to sensitivity of conducting polymers to environmental conditions (e.g., air, oxygen, moisture, high temperature and chemical solutions), lithographic techniques present significant technical challenges when working with these materials(4). For example, current photolithographic methods, such as ultra-violet (UV), are unsuitable for patterning the conducting polymers due to the involvement of wet and/or dry etching processes in these methods. In addition, current micro/nanosystems mainly have a planar form(5,6). One layer of structures is built on the top surfaces of another layer of fabricated features. Multiple layers of these structures are stacked together to form numerous devices on a common substrate. The sidewall surfaces of the microstructures have not been used in constructing devices. On the other hand, sidewall patterns could be used, for example, to build 3-D circuits, modify fluidic channels and direct horizontal growth of nanowires and nanotubes. A macropunching method has been applied in the manufacturing industry to create macropatterns in a sheet metal for over a hundred years. Motivated by this approach, we have developed a micropunching lithography method (MPL) to overcome the obstacles of patterning conducting polymers and generating sidewall patterns. Like the macropunching method, the MPL also includes two operations (Fig. 1): (i) cutting; and (ii) drawing. The "cutting" operation was applied to pattern three conducting polymers(4), polypyrrole (PPy), Poly(3,4-ethylenedioxythiophen)-poly(4-styrenesulphonate) (PEDOT) and polyaniline (PANI). It was also employed to create Al microstructures(7). The fabricated microstructures of conducting polymers have been used as humidity(8), chemical(8), and glucose sensors(9). Combined microstructures of Al and conducting polymers have been employed to fabricate capacitors and various heterojunctions(9,10,11). The "cutting" operation was also applied to generate submicron-patterns, such as 100- and 500-nm-wide PPy lines as well as 100-nm-wide Au wires. The "drawing" operation was employed for two applications: (i) produce Au sidewall patterns on high density polyethylene (HDPE) channels which could be used for building 3D microsystems(12,13,14), and (ii) fabricate polydimethylsiloxane (PDMS) micropillars on HDPE substrates to increase the contact angle of the channel(15).

Generation of micropatterns of conducting polymers and aluminum using an intermediate-layer lithography approach and some applications

Conducting polymers, because of their promising potential to replace silicon and metals in building devices, have attracted great attention since the discovery of high conductivity in doped polyacetylene in 1977. Lithographic techniques present significant technical challenges when working with conducting polymers. Sensitivity of conducting polymers to environmental conditions (e.g., air, oxygen, moisture, high temperature, and chemical solutions) makes current photolithographic methods unsuitable for patterning the conducting polymers due to the involvement of wet and/or dry etching processes in those methods. Existing non-photolithographic approaches have limitations in throughput, resolution, or electrical insulation. Therefore, an intermediate-layer lithography (ILL) approach has been recently developed by my group to produce conducting polymer micro/nanostructures. In the ILL method, an intermediate layer of an electrically insulating polymer is coated between the substrate and a layer of the conducting polymer to be printed. Subsequently, the conducting polymer is printed through mold insertion using a hot-embossing process. The current hot-embossing based methods face the obstacles of residual layer and depth of field (i.e., the height variation in the mold structures). In contrast, the ILL approach does not leave a residual layer in the material of interest, making conducting polymer patterns isolated from one another and avoiding the shorting problem in the electrical applications of these patterns. Furthermore, in the ILL, the height variation potentially existing among the mold structures has been transferred to the intermediate layer, ensuring that all patterns in the mold have been properly transferred to the conducting polymer layer. In addition to conducting polymers, the ILL can also be applied to pattern metals as well as other types of polymers. This paper gives a review of this ILL method and reports the results that we have achieved to date, including generation and applications of single and multiple layers of microstructures of conducting polymers and aluminum.

Theoretical Investigation of Excited States of Large Polyene Cations as Model Systems for Lightly Doped Polyacetylene.

Electronic excitations of polyene cations with chain lengths of up to 101 CH units were investigated as model systems for lightly doped polyacetylene (PA). Since high level ab initio calculations such as complete active space perturbation theory (CASPT2) are limited to systems with about 14 CH units, the performances of time-dependent Hartree-Fock (TDHF) and time-dependent density functional theory (TDDFT) were evaluated. It turned out that TDDFT excitations energies are much more accurate for polyene cations than for neutral polyenes. The difference between TDHF and TDDFT excitation energies for the first allowed excited state of C49H51(+) is only 0.30 eV with pure DFT and 0.21 eV with a hybrid functional. For open-shell systems, pure DFT is found to be superior to DFT-hybrid functionals because it does not suffer from spin-contamination. Pure TDDFT excitation energies and oscillator strengths for small open-shell polyene cations compare well with high level ab initio results. Excitation energies are found to be almost independent of the geometry, i.e., the size of the defect. Localization of the defect, however, shifts oscillator strengths from the HOMO-LUMO transition to higher lying excited states of the same symmetry. Lightly doped PA is predicted to exhibit several strong absorptions below 1 eV.

Linking model Hamiltonians to ab initio and semiempirical methods in descriptions of impurities in conjugated polymers

AbstractSemiempirical and ab initio electronic structure and model Hamiltonian calculations of the undoped and doped polyacetylene (PA) chain are presented. As a general model Hamiltonian we use the Su–Schrieffer–Heeger (SSH) model combined with the Pariser–Parr–Pople (PPP) model with site‐type impurities. More precisely, band gap and charge distributions of a single conducting PA chain bonding with several atomic and molecular radicals as impurities were investigated. From a comparison between the electronic and SSH‐PPP calculation it was possible to determine what impurity actually corresponds to the charge distribution obtained with model calculations. Therefore, it is shown within the present results what impurities are being represented in model calculations. This correspondence is fundamental in determining the behavior of molecular circuits and molecular devices. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005

Optical properties of potassium-doped polyacetylene

The optical reflectance of polyacetylene doped with high concentrations of potassium has been measured, and the optical properties estimated by Kramers–Kronig analysis. The samples, doped by a vapor-phase technique to y≈0.08 and 0.18, showed strong doping-induced infrared absorption at ∼900, 1270, and 1390 cm −1. These experiments were motivated by calculations of the infrared absorption which showed that whereas there are only small differences in the infrared spectra for isolated solitons and isolated polarons, there is a dramatic difference between the high-concentration polaron and soliton lattices. The shapes of the absorption spectra are rather similar but the absorption for the polaron lattice is 13 orders of magnitude weaker than that of the soliton lattice. The observation of these features at high doping levels is inconsistent with both the polaronic metal and strongly disordered Peierls insulator models for highly doped polyacetylene and furthermore suggests that solitonic defects maintain their integrity to very high doping levels.

FeCl4− doped polyacetylene near the metalinsulator transition: Anomalous magnetoresistance at high fields up to H30T

We report on the anomalous high field magnetoresistance of FeCl 4 - doped polyacetylene films near the metal-insulator transition in the temperature range T = 0.6-1.4K and the magnetic field range H = 0-30T. When doped polyacetylene approaches to the metal-insulator transition region from the metallic side, the magnetoresistance of FeCl 4 - doped polyacetylene shows two positive peaks, which is different from the case of iodine or ClO 4 - doped polyacetylene showing only one broad peak. The results could he understood in terms of the compensation for the internal exchange field of a FeCl 4 - ion by the external high magnetic field.

Dimensional changes as a function of charge injection for trans-polyacetylene: A density functional theory study

Charge-induced dimensional changes allow conducting polymers and single walled carbon nanotubes to function as electromechanical actuators. The unit cell of the prototypical conducting polymer, trans-polyacetylene, was calculated as a function of charge injection using density functional theory in combination with ultrasoft pseudopotentials using the solid-state Vienna ab initio simulation package. Test calculations on the charged pyridinium molecular ion give results in good agreement with the experimental geometry. Strain versus charge relationships are predicted from dimensional changes calculated using a uniform background charge (“jellium”) for representing the counterions, which we show provides results consistent with experiment for doped polyacetylenes. These jellium calculations are consistent with further presented calculations that include specific counterions, showing that hybridization between the guest dopant ions and the host polyacetylene chains is unimportant. The lack of guest–host orbital hybridization allows a qualitative rigid band interpretation of the amount of charge transfer for both acceptor and donor doping. For polyacetylene, asymmetry of strain along the chain with respect to the sign of the charge is predicted: negative charge elongates and positive charge shortens the polymer. For charge less than 0.05e per carbon, an approximately linear dependence is obtained for the dependence of chain-direction strain on the amount of injected charge.

The effects of pressure and magnetic field on the charge transport of heavily FeCl 4− doped polyacetylene

The effects of hydrostatic pressure and magnetic field on the charge transport of oriented polyacetylene (PA) films heavily doped with FeCl 4 − have been studied in the temperature range 0.37–300 K. It was found that application of pressure increases the room temperature conductivity and decreases the resistivity ratio ρ r=ρ(0.37 K)/ρ(300 K) by ∼20–30%. At T<2 K the temperature dependence of resistivity ρ( T)∼ln T at ambient pressure and at 10 kbar. Transverse magnetoresistance (MR) at 10 kbar was found to be negative, linear and almost temperature independent at T<2 K. The observed low temperature ρ( T) and MR behavior has attributed to weak localization which accompanied by the effect of saturation of electron dephasing by two-level systems of a special type. The stronger behavior of ρ( T) and MR at T>2 K has associated with further suppression of weak localization due to more effective dephasing effect by low energy vibrational excitations.

Electronic structure and optical spectroscopy of conducting electrochromic devices

Interest in conductive organic polymers has considerably increased since the discovery in 1977 of the doped molecule polyacetylene. Recently, polymers of dithienopyrrole (DP), dithienothiophene (DT) and thionaphtheneindole (TNI) have been synthesized electrochemically showing for several monomer ratios good electrochromic and conducting characteristics.

Quantum transport in AuCl 3 doped polyacetylene studied by ESR

Starting with a review of general principles of transport processes in polyacetylene (PA) which can be studied by electron spin resonance (ESR) new results on highly doped PA are presented. The AuCl 3 doped PA samples stored under vacuum at room temperature in ESR sample tubes reach a steady state in the temperature dependent intensity and linewidth behavior after three to four month storage. The ESR spectra show two lines with an equal g-factor. In particular, the linewidth of the small line demonstrates a remarkable property. The temperature dependence of the linewidth shows a maximum of Δ B=0.30 mT at 30 K, and it is constant at Δ B=0.17 mT above this temperature in the whole temperature region between 70 and 300 K. The ESR data are discussed in a two spin model of delocalized states at the PA chain and fixed spins near the dopants. Broadening and motional narrowing influence the ESR linewidth. The interpretation points to the metallic behavior of the highly doped PA at low temperatures.

Magneto thermoelectric power of the doped polyacetylene

Abstract Thermoelectric power (TEP) and electrical conductivity of the metallic polyacetylene (PA) doped with AuCl 3 and I 2 are measured under high magnetic field up to 17 Tesla. We have observed the following two remarkable behaviors in the TEP results; (1) the temperature dependence of TEP for the iodine and metal-halide doped polyacetylene show clear difference at T

Magnetoresistance of the metallic polyacetylene

The temperature dependence of the zero field resistivity, ρ( T), and the magnetoresistance (MR) of polyacetylene (PA) doped with iodine, metal-halide (AuCl 3, FeCl 3) and perchlorate are measured. The results of doped PA are different for each dopant and for the degree of aging. The ρ( T) of the metal-halide and the perchlorate doped PAs show a resistivity minimum near T*≈200 K and the weak temperature dependence at low temperature. In particular, some of the perchlorate doped PA samples show the positive temperature coefficient of resistivity (TCR) from T=1.5 K to T=300 K with resistivity ratio ρ( T=1.5 K)/ ρ( T=300 K)=0.5∼0.7 depending on the samples. The MR is negative for all of the metallic PA samples. Both transverse ( J⊥ H) and longitudinal ( J‖ H) MR show similar magnetic field dependencies, although the magnitude of the transverse MR is larger than that of the longitudinal MR. For the aged samples, the ρ( T) increase more rapidly upon cooling than that of the fresh samples. The MR of the aged samples is positive. The localization–interaction theory is examined for the observed ρ( T) and MR data of doped PA. But the model of interchain charge transfer bridged by the dopants seems to explain the negative MR as well as the metallic temperature dependence of resistivity for the perchlorate doped polyacetylene.

Conjugated polymer surfaces and interfaces in polymer-based light-emitting diodes

Since the discovery of high electrical conductivity in doped polyacetylene in 1977, π-conjugated polymers have emerged as viable semiconducting electronic materials for numerous applications. In the context of polymer electronic devices, it is of critical importance to understand the nature of the electronic structure of the polymer surface and the interface with metals. It has been shown that, for conjugated polymers, photoelectron spectroscopy, especially in connection with quantum chemical modeling, provides a maximum amount of both chemical and electronic structural information in one type of measurement. There is no such thing as the ideal metal-on-polymer contact; there is always some chemistry that occurs at the interface. © 1998 John Wiley & Sons, Ltd.

Carrier transport in highly doped polyacetylene

By use of a modified Naarmann's method, we synthesized good quality polyacetylene films. The films were doped highly with iodine and iron chloride. Taking advantage of a scanning electron microscope, we observed contacts between fibres in the sample. At the contact of two fibres, it produced a contact potential barrier between two mutual contact polyacetylene chains of respective fibres and formed a small tunnel junction. Under the thermal activation, electrons of charged solitons in the soliton band can jump into nearby neutral solitons. These jumping electrons can produce thermally activated voltage fluctuations across junctions that impel free electrons to participate in the tunneling conduction. In view of this, the voltage fluctuation probability P( V T ) raised by the thermal fluctuation voltage V T was derived. By use of the fluctuation-induced tunneling conduction theory, and the effective medium theory, the d.c. conductivity formula of the sample was achieved. We measured the temperature dependence of d.c. conductivities of samples and showed that the formula was in good agreement with experimental results.

Conjugated Polymer Surfaces and Interfaces for Light-Emitting Devices

Since the discovery of high electrical conductivity in doped polyacetylene in 1977, π-conjugated polymers have emerged as viable semiconducting electronic materials for numerous applications. In the context of polymer electronic devices, one must understand the nature of the polymer surface's electronic structure and the interface with metals. For conjugated polymers, photoelectron spectroscopy—especially in connection with quantum-chemical modeling—provides a maximum amount of both chemical and electronic structural information in one (type of) measurement. Some details of the early stages of interface formation with metals on the surfaces of conjugated polymers and model molecular solids in connection with polymer-based light-emitting devices (LEDs) are outlined. Then a chosen set of issues is summarized in a band structure diagram for a polymer LED, based upon a “clean calcium electrode” on the clean surface of a thin film of poly(p-phenylene vinylene) (PPV). This diagram helps to point out the complexity of the systems involved in polymer LEDs. No such thing as “an ideal metal-on-polymer contact” exists. There is always some chemistry occurring at the interface.

Hartree-Fock calculations for the electronic and lattice structures in heavily sodium doped polyacetylene

We evaluated 3D interactions in highly Na-doped polyacetylene, (CH) x, reasonably based on the structure reported in an X ray experiment. Interchain transfers (ICTs) via dopants estimated quantum chemically are found to reach up to 0.93 eV and spread over five sites on each adjacent chain at doping concentration, 11.1%, Screened Coulomb interactions are evaluated as Thomas-Fermi potential for quasi ID conductors numerically, to estimate reasonable interchain Coulomb (ICC) and dopants' Coulomb (DC) potentials. As the intrachain Hamiltonian, SSH+extended Hubbard model is used. The Hartree-Fock (HF) ground state with geometry optimization is soliton lattices out-of-phase ordered. The gap little depends on chain length and is extrapolated to 1.3eV in infinite chain limit. So rather large ICT in itself cannot lead to metallic state in HF approximation, and electron correlation seems to be important.

Low temperature thermoelectric power of the metal-halide doped polyacetylene

We have measured thermoelectric power (TEP) of the doped polyacetylene (PA) from room temperature down to liquid helium temperature. The dopants are AuCl 3, NbCl 5, FeCl 3 and I 2. The overall TEP data show the diffusive metallic property, i.e. the TEP is positive and it decreases quasi-linearly upon cooling. For the metal-halide doped PA, the TEP is temperature independent with small magnitude about 0.2~0.6μV/K below 17K, while the quasi-linear temperature dependent TEP is observed for the iodine doped PA in the same low temperature regime. The concentration dependence of TEP for AuCl 3 doped PA shows that the TEP becomes negative at T<20K~30K depending on the doping concentration with a broad minimum peak at low temperature. The result indicates that the effect of dopant to the PA chain is important to understand the metallic nature of heavily doped PA.

The effect of high magnetic field on thermoelectric power of doped polyacetylene

We have measured the temperature dependent thermoelectric power (TEP) of doped polyacetylene (PA) under the high magnetic field up to 20 tesla. The dopants are I 2, FeCl 3, AuCl 3and NbCl 5. The overall temperature dependence is characteristic to that of the diffusive metals, i.e. the TEP is positive and it decreases quasi-linearly upon cooling. However, the zero field TEP, S(T, H=0T), shows significant differences between the iodine doped PA and the other metal-halide doped ones at low temperature. While the S(T, H=0T) for iodine doped PA is quasi-linear in temperature down to 4.2 K, the S(T, H=0T) of metal-halide doped samples become temperature independent below T≅20 K and some of them show even negative TEP with a broad minimum peak at low temperature. At H=20T, both iodine and metal halide doped PA shows an abrupt decrease of 1~2 μV/K in TEP at T~70K, except the most heavily doped [CH(AuCl 4) y] x where no such drop appears. In the low temperature region, the ΔS(T)=S(T,H=20T)-S(T,H=0T) of metal-halide doped PA becomes more negative and the minimum peak of TEP shifts slightly to higher temperature. Similar tendency is observed at zero field TEP of [CH(AuCl 4) y] x as we increase the doping concentration y. For the iodine doped PA, the low temperature AS(T)=S(T,H=20T)-S(T,H=0T) is more or less the same as that of T~70K where the abrupt jump occurred, i.e., the S(T,H=20T) of iodine doped PA remains quasi-linear as a function of temperature down to 4.2 K. The magneto resistance ρ(T,H) of these samples is also measured and the results are compared with the above S(T,H) data. Since no appreciable amount of anisotropy of the stretch oriented PA with respect to the applied magnetic field direction is observed in S(T,H) and ρ(T,H) and furthermore, because of the significant difference of S(T,H) between the iodine doped PA and the metal-halide doped ones, the spin-spin interaction between the conduction electron spin in the metallic PA chain and the localized spin in the metal-halide dopant located nearby the polymer chain could be the prime origin of the observed magneto TEP phenomena.