Doping Of Polyacetylene Research Articles

Microwave conductivity of alkali-metal doped polyacetylene

The temperature dependence of microwave conductivity of potassium doped polyacetylene film is reported. The measurement has been performed with 4.5 GHz cylindrical cavity made of copper using the cavity perturbation method. The high density polyacetylene films are synthethized following the modified Shirakawa method. Doping of polyacetylene with potassium has been accomplished by vapor phase method. The temperature dependence is similar to the results of dc conductivity of the p-type doped polyacetylene films.

Soliton model of metallic state in polyacetylene

Doping of polyacetylene by more than 4–7% causes an insulator-metal transition, as evidenced by the appearance of sizable Pauli susceptibility and large conductivity. The nature of the metallic state has been the subject of wide speculation. We show that there is strong evidence, mainly from optical absorption measurements, that the soliton lattice characteristics of doped polyacetylene below the transition persists in the metallic state. Another strong piece of evidence for the soliton lattice model is the existence of samples in which free carrier absorption is present at 300 K, but disappears at low temperatures. We show that other proposed models of the metallic state (polaron lattice, uniform chain and polson model) cannot explain the data.

N doping of polyacetylene

We achieve N doping of polyacetylene by potassium in vapor phase. This was performed on samples oriented by Akagi's method. Doping kinetic is controlled by in situ conductivity measurements and exhibits two different steps. The first step is rather fast (one hour) and leads to dopant fixation in the sample. The second one, consists in annealing the doped polyacetylene and is rather slow (days). After the second step conductivity is in the range 10 4 ω −1 cm −1. The doped samples are very sensitive to any oxidation but remarkably stable, either in vacuum or in potassium vapor. They remain nicely oriented after doping.

Synthesis and properties of polyacetylenes with electron donor substituents

New anthracene- and carbazole-containing diacetylenes have been synthesized and subjected to solid phase polymerization, leading to corresponding polydiacetylenes having a polymer chain of ene-ine structure. Doping of the polydiacetylene with iodine depends on its degree of ordering and also on the nature of the electron donor substituent. It is established that there is a maximum on the excitation spectra for the photoconductivity of polyacetylene, located beyond the edge of the optical absorption fundamental. The “internal” doping of polyacetylene with iodine is described: on polymerization of the iodine-containing diacetylene, partial separation of iodine occurs, which results in doping of the polymer formed. The maximum on the excitation spectra for photoconductivity of polyacetylene, located in the region of the absorption of electron donor groups, is associated with “sensitized” photoconductivity, consisting in electron transfer from an excited electron donor substituent into the conductivity zone of the polydiacetylene chain.

Electronic structure of highly conducting conjugated polymers: evolution upon doping of polyacetylene, polythiophene, and polyemeraldine

The electronic properties of three types of conducting polymers: trans-polyacetylene (proto-typical of systems with a degenerate ground state), polythiophene (as an example of compounds with a nondegenerate ground state), and polyemeraldine (which can be doped via protonation) are reviewed. The structural and electronic band structure properties of these systems are studied at various defect concentrations corresponding to undoped, lightly doped, and highly doped polymers. Geometry optimizations of oligomeric equivalents to the undoped and doped polymers are performed using the semi-empirical MNDO and AM1 methods. The electronic band structures are calculated using the VEH method. The interpretation of the optical absorption data is discussed in terms of interband transitions; for doped trans-polyacetylene including soliton defects and for doped polythiophene including bipolaron defects. For highly doped trans-polyacetylene and polythiophene as well as for protonated polyemeraldine, the electronic structure of a polaron lattice conformation is discussed and shown to be in agreement with existing optical and magnetic data on these polymers.

Electron transfer from carbanionic salts to linear sequences of conjugated double bonds, 1. Mechanism of n doping of polyacetylene

AbstractIt is shown that the mechanism of polyacetylene (PA) reduction (or n “doping”) by alkaline carbanionic salts and butyllithium is a simple electron transfer without addition. In this reduction reaction the dicarbanionic dimer of 1,1‐diphenylethylene (DD2– Na2+) is quantitatively converted to 1,1‐diphenylethylene. The reduction by 3‐methyl‐1,1‐diphenylpentyllithium produces free radicals which deactivate in solution by coupling and disproportionation. But the strong dependence of the ratio of disproportionation to coupling of these radicals on solvent polarity is unusual: no coupling is observed in diethyl ether or pentane, while it is the most important reaction in THF. sec‐Butyllithium in pentane also reduces PA by a simple electron transfer process. The “doping” levels can be deduced accurately from the quantitive analysis of the by‐products by gas chromatography.

On the role of inorganic fluorine chemistry in the study of synthetic metals

The intercalation of metal hexafluorides (MF6) into graphite proceeds according to the reaction nC + MF6 → Cn+x(MF6−)x(MF6)1−x where x is the degree of charge transfer. The latter can be determined by magnetic measurements. It varies approximately linearly with the electron affinity of the MF6.The doping of polyacetylene by MF6 is believed to proceed by a similar reaction.

A neutron diffraction study on the doping of polyacetylene by SbF 5, I 2 and IBr

The doping of deuterated polyacetylene, [CD] n , with SbF 5, I 2 and IBr was studied by neutron diffractometry. New structures were found in all cases. The diffraction patterns resemble in many details that of [CD] n doped by AsF 5, but show different degrees of disorder. A correlation between the conductivity and the apparent particle size appears to exist. Evidence for one-dimensional scattering of the polymer chains was found.

Doping of polyacetylene with tin chloride - Mössbauer, EPR and Raman spectroscopic studies

Polyacetylene film, containing varying amounts of trans isomer, has been chemically oxidized with SnCl 4. The reaction product has been studied by Mössbauer spectroscopy. The results suggest the existence of SnCl 5 − as the inserted species. From the temperature dependence of the recoil-free fraction the Mössbauer lattice temperature, θ, was estimated as 95K. This low value of θ indicates a significant mobility of SnCl 5 − ions at RT. Raman and EPR results are consistent with the Mössbauer effect measurements. Upon doping a broad ( Δ Hpp = 5 G ) EPR line, which is a super-position of the lines characteristics of all trans polyacetylene and cis-rich polyacetylene, is transformed into a narrow ( Δ Hpp = 0.8 G ), slightly assymetric ( A/ B = 1.23 ) line characteristic of partially oxidized trans-(CH) x chain of high conductivity. The same doping induced isomerization can also be evidenced by Raman spectroscopy showing the disappearance of cis-(CH) x modes after the oxidation.

A Synchrotron Scattering Study on the Doping of Polyacetylene by I2

A Synchrotron Scattering Study on the Doping of Polyacetylene by I2

A neutron diffraction study on the doping of polyacetylene by AsF5

AbstractThe doping of deuterated polyacetylene (cis and trans) with AsF5 was studied by neutron diffractometry. A method of optimize the crystallinity of the doped material is described. Evidence for the presence of two species in the doped polymer which are probably AsF6− and AsF3 is presented. Model calculations based on a series of [CDxH1‐x(AsF5)y]n samples support a “first‐stage” intercalation structure with a graphitic structure.

MÖSSBAUER SPECTROSCOPY STUDIES OF POLYACETYLENE DOPED CHEMICALLY AND ELECTROCHEMICALLY WITH IRON CHLORIDES

Doping of polyacetylene with iron chloride complexes has been studied by MBssbauer spectroscopy. It was proved that the doped polymer undergoes degradation in air manifested by the formation of FeOlxaE^O with the simultaneous chlorination of the double bond.

Isomerization mechanisms from cis to trans form in polyacetylene

Mechanisms of cis-trans irreversible isomerizations occurring in both thermal treatment and doping of polyacetylene are presented and examined by means of MINDO/3 molecular orbital calculations on some finite polyenes. It is predicted that the thermal isomerization proceeds along the internal rotation of (-CH=CH-) unit around two carbon-carbon double bonds via the transition state having a biradical nature. Meanwhile, the isomerization by doping is rationalized by the mechanism that the cis segment between two doping sites is converted into the trans-cisoid form which rotates easily around two single bonds to yield some trans forms in (CH) x chain.

Stability of various doping species in trans-polyacetylene

Polyacetylene, a simple conjugated organic polymer, a material of strong interest if doped by various chemical species such as iodine or antimony pentafluoride : its electrical conductivity increases by more than twelve orders of magnitude. By increasing the dopant concentration one obtains a semiconductive or a metallic regime. Such properties allow us to make electronic material and then devices by convenient n or p type doping of polyacetylene. However,it is necessary to determine the thermal stability of the various dopant species. In this paper, we compared the stability of iodine, SbF5 and CF3SO3H dopants by studying the mass loss and the electrical conductivity decrease at various temperatures from 20‡C up to 180‡C. It is shown that only SbF5 is a relatively stable dopant up to 80‡C, a temperature which may be reached in some active electronic devices. Raman spectroscopy allowed us to measure the ratio of I−3 to I−5 ions during the desorption process and to propose a possible chemical reaction which produces gaseous iodine from the active dopant species.

Doping of polyacetylene by diffusion of iodine

The solubility limit and diffusion coefficient of I 2 in (CH) x polymer have been measured with a radiotracer technique. The concentration of iodine in the polymer is a function of the surrounding concentration outside the film at equilibrium (free enthalpy of solubility = − 0.20 eV). The data are consistent with the following mechanism: liquid state diffusion of the solution in between the fibrils and solid state diffusion of iodine inside the fibrils. The macroscopic diffusion coefficient throughout the film is equal to 10 −9cm 2sec −1. These results restrict the present (CH) x polymer to heterolithic device applications after encapsulation. Monolithic substrate application will require a further inhibition of diffusion.

Doping of polyacetylene by diffusion of iodine

Doping of polyacetylene by diffusion of iodine

Oxygen doping of polyacetylene determined by dielectric techniques

Oxygen doping of polyacetylene determined by dielectric techniques