Reductive doping alkali metals

Electrochemical data, obtained in the early work by Baughman et al. [92,93] have indicated several transitions, and suggest the formation of distinct 

Reduction can be effected by doping with alkali metals, either in the vapour phase or in solution, e.g. with naphthalide salts in THE Electrochemical doping is very well possible, for instance with LiB(Me)4 or NaB(Ph)4 in solution with a polyacetylene cathode. The representation (CH)M is often used to denote a certain composition. 

Alkali-doped polyacetylene is extremely air-sensitive and deteriorates much more quickly than oxidatively doped polyacetylene. But, whereas the latter degrades rapidly upon heating as a result of polymer-dopant reactions that alter the chain, alkali-doped polyacetylene is surprisingly stable thermally, up to 200°C. This can be exploited to anneal cis-rich doped samples, which leads to a considerable decrease of disorder and evolution towards the trans lattice [88]. Especially in K-doped samples, this leads to a strong conductivity increase. 

The cell constants for stage-1 compounds have been more precisely determined over the years. It must be emphasized here, as it has been before and certainly will be again later, that the availability of oriented polyacetylene has been crucial for the progress made in the interpretation of the diffraction data. For the quantitative comparison of intensities, Shirakawa polyacetylene is still used because its isotropic diffraction can be compared with powder calculations and does not need the tricky Lorentz corrections of fibre symmetries. Moreover, Shirakawa polyacetylene is known for its relatively high crystallographic coherence and the absence of impurity reflections. 

Layers in invariant which chains layers rotate during dopant insertion 

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Through reduction or oxidation of the molecule by a dopant molecule. Atoms or molecules with high electron affinity, such as iodine, antimony pentafluoride (SbCls), or 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), may oxidize a typical organic semiconductor such as poly(p-phenylene) derivatives, leaving them positively charged. Reduction, i.e., addition of an electron, may be obtained by doping with alkali metals. 

Fig. 1 H uckel energy levels of Ceo together with one component of the triply degenerate ti set of molecular orbitals that become populated upon alkali metal doping or electrochemical reduction.

We have considered several possible explanations for the disappearance of most of the Hg modes. First, the addition of alkali metal atoms to the lattice will introduce symmetry reduction due to A-C o interactions, which will tend to broaden the Hg modes as their degeneracy is broken. However, on the scale of our resolution these effects should be small and, as discussed below, further doping results in a reappear-... 

Addition of methanol to 2-methylene-1,3-dioxepane (28) leads to the corresponding seven-membered cyclic orthoacetate (156) (Equation (23)) <86TL1587>, and electrochemical reduction of 1,3-dioxepan-2-one (157) in an electrolyte containing alkali metal ions affords orthoester derivatives (158), useful for stabilizing /i-doped polyacetylene as the anode-active material of a battery (Equation (24)) <85JAP(K)60I2628I>. 

The two main mechanisms [38,179,190,196,198,203] expected to be behind the reduction of <]> (and b) in the presence of the fluoride interlayer are (a) interaction of the fluoride with the metal and organic layers and its dissociation. The liberated Li would not only dope the polymer but, importantly, either create a low work function contact (Li has a low work function [204-206]) or, in the form of Li ions, build a doped region of space charge at the cathode/polymer interface [40,41] (b) a dipole-induced work function change due to either the large dipole moment of the oriented fluoride molecules [183,207,208] or the interfacial transfer of charge from the adsorbed fluoride layer [50] (in particular fi-om the alkali metal atoms [71]) to the A1 cathode. 

Naphtalides, alkalides, and alkali metals are sufficiently powerful to reduce Ge and Si salts to the elements. Si nanocrystals have been prepared in solution by the reduction of the halides with Na, Li naphthalide, and hydride reagents [216-219]. Similarly, Ge nanocrystals have been made by the reduction of GeCL with Li naphthalide in THF [217]. TEOS (Si(OEt)4) is readily reduced by sodium to yield Si nanocrystals. Si and Ge nanocrystals are frequently covered by an oxide layer. Y2O3 nanocrystals have been made by the alkalide reduction of YCI3 followed by oxidation by exposure to ambient conditions [220]. Yittria nanocrystals could be doped with Eu to render them phosphorescent [221]. ZnO nanoparticles have been prepared from zinc acetate in 2-propanol by the reaction with water [222]. Pure anatase nanocrystals are obtained by the hydrolysis of TiCL with ethanol at 0°C followed by calcination at 87° C for 3 days [223]. The growth kinetics and the surface hydration chemistry in this reaction have been investigated. 

Doping with alkali metals is an example of n-type doping (reduction of the polymer chain). Our calculations therefore include negatively charged defects (solitons) only. The impurity potential is in this case attractive (see Eq. (4)). Even though there is no exact electron-hole symmetry in the electronic spectrum in the presence of the extended Hubbard term (see Eq. (6) below), the properties of a p-type doped system are very close to those of a n-type doped system. Therefore, all results presented in the next section also hold for the case of p-type doping. 

In our first paper [4] we presented a mixture of conductivity and EPR studies. We interpreted the temperature/phase dependence of the EPR line shapes of aluminium trichloride doped HAT6 in terms of Dysonian theory, but this later proved to be incorrect. We later showed that both the g value and the EPR line width are dependent on the orientation of the director relative to the field and this leads to a complex, line shape in powder samples [7], Just as p-doped, hole conductors can be produced by oxidation of discogens with pi excessive cores using aluminium trichloride, aluminium tribromide or NO+X", n-doped, electron conductors can be produced by reduction of discogens with pi deficient cores using alkali metals [8]. 

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