Protonic doping

Han and Elsenbaumer also note that the BP initially formed can react with neutral polymer to form two distinctly different polarons via interchain electron transfer. After twenty-four hours, our optical spectra are unchanged, and have measurable ESR activity. However, in contrast to alkoxy-PPV polymer, we do not observe a typical polaronic absorption spectrum, but rather one almost identical to the bipolaron obtained from SbCl5 doping of 10-5 M solutions in CH2CI2. A possible interpretation is one which allows for P and BP states coexisting in dynamic equilibrium, with the bipolaron dominating the optical absorption. The absorption characteristics of the protonically doped polyenes are shown in Table II compared to the same samples doped with SbCl5. 

One can conclude from this data that although polaron states are present, they are present to the extent of 1% or less. Thus it is not surprising that the dominant optical absorption is bipolaronic. Since Han and Elsenbaumer (26) do not report a quantitative spin concentration for their protonically doped PPV,... 

An additional inconsistency in comparing protonic versus SbCl5 doping is the fact that the BP absorption maxima for the protonically doped species is blue-shifted from the SbCl5-doping maxima. One possible explanation is that the position of proton attack, as proposed by Han and Elsenbaumer (26) is different in our system. The PPV oligomers would be resistant to protonation at the 4-position due to the disruption of the chain conjugation sequence, and position of attack is dominanted by the bipolaronic stability. However, in our model compounds, several positions are available for protonation. For compound 6, we can envision attack at five positions ... 

We are now concentrating our synthetic efforts on repeat units capable of oxidative and protonic doping in order to determine AX(3)... 

Permanently doped polymers, concerned with chemical or protonic doping. The charges that appear on the polymer chains are compen-... 

Using chemical or protonic doping, the electric charges on the polymer chains are compensated by counterion injection. In the case of protonic doping (essentially in polyaniline), the addition of protons does not change the overall number of electrons in the chain skeleton. But one of the two electrons of the nitrogen doublet become caught in the N—H bond, and then the effective number of electrons available for the tt system is modified. 

Polyaniline (137) is one of the most promising conductive polymers and the conductivity could be reversibly controlled by oxidation or protonic doping mechanisms228,229. In addition, polyaniline displays good environmental and thermal stability, and its undoped form is solution processable from both organic and aqueous acid solutions. The polymerization of aniline is usually carried out by a chemical or electrochemical oxidation reaction230,231. However, photochemical methods toward the preparation of poly aniline have recently been reported232-240. 

Another material—polyaniline in its quinoid-benzenoid-diimine form—has recently been reported to be compatible with aqueous electrolytes both in the oxidized and reduced states. As opposed to the conventional method of p-doping organic polymers by oxidative removal of electrons from the polymer 7r-system, polyaniline can be proton doped in an aqueous protic acid (HCl or HBF4) to a metallic (S — 5 cm ) iminium salt. Cells con-... 

Solutions of EB may be also readily doped with a range of metal salts and Lewis acids in a process (Equation 4.2) reminiscent of the Bronsted acid doping of EB described earlier. Similar to protonic doping, binding of the metal ions to imine N sites on the EB chains is believed to occur, leading to conducting PAn products of the general type 14. 

However, the most significant dependence of the conductivity of PAn is on the proton-doping level.19 The maximum conductivity occurs when PAn is 50% doped by protons, to give the polaron lattice structure shown in Figure 5.1. Under these conditions, the conduction mechanism is similar to that for the other polymers described, with the polaron states overlapping to form midgap bands. The electrons are thermally promoted at ambient temperatures to the lower energy-unfilled bands that permits conduction.20... 

Each charged site on the PAN] chain is accompanied by a counteranion, of course. Therefore, in analogy with the situation for other conducting polymers, the protonation process is called doping. This is a partial analogy, however, since proton doping of emeraldine is not an oxidative process. Results obtained with various... 

Of these, protoemeraldine and emeraldine are conducting forms. However, they are conducting only when they are protonated. This is called the protonic doping and Chiang and MacDiarmid [147] discovered for the protonic doping of these states that the pKa of polyaniline is linearly related to pH of the medium as... 

Polyaniline was first prepared at the turn of the century. Several oxidation states are known. The conductivity and the color of the material vaiy progressively with oxidation. Only one form, however, known as the emeraldine salt, is truly conducting. The material can be prepared readily by either electrochemical or chemical oxidation of aniline in aqueous acid media. Common oxidants, such as ammonium peroxydisulfate, can be used. Flexible emeraldine films can be cast from solutions of A methylpyrrolidone and made conductive by protonic doping. This is done by dipping the films in acid or exposing them to acid vapors. The process results in protonation of the imine nitrogen atoms ... 

Aniline was the first example of the conjugated polymers doped by proton, it can be chemically oxidized by ammonium peroxydisulfate (APS). PANI has the advantages of easy synthesis, low-cost, proton doping mechanism, and is controlled by both oxidation and protonation state. Polyanilines are commonly prepared by the chemical or electrochemical oxidative potymerization of the respective monomers in acidic solution. But, other potymerization techniques have also been developed, including ... 

This significantly differs from redox doping (e.g., oxidation or reduction), which involves the partial addition (reduction) or removal (oxidation) of electrons to or from the pol5mier backbone. Thus proton doping is a major characteristic of PANl, differing from other CPs. The ES form is the state with the highest conductivity. ... 

The conductivity may depend on other factors for instance on the pH of the contacting solution (proton doping in the case of polyaniline) (Fig. 6.7) or on the presence of electron donor molecules in the gas phase. 

Polyaniline is the conducting polymer most commonly used as an electrocatalyst and immobilizer for biomolecules [258-260]. However, for biosensor applications, a nearly neutral pH environment is required, since most biocatalysts (enzymes) operate only in neutral or slightly acidic or alkaline solutions. Therefore, it has been difficult or impossible to couple enzyme catalyzed electron transfer processes involving solution species with electron transport or electrochemical redox reactions of mostly polyaniline and its derivatives. Polyaniline is conducting and electroactive only in its protonated (proton doped) form i.e., at low pH valnes. At pH values above 3 or 4, polyaniline is insulating and electrochemically inactive. Self-doped polyaniline exhibits redox activity and electronic conductivity over an extended pH range, which greatly expands its applicability toward biosensors [209, 210, 261]. Therefore, the use of self-doped polyaniline and its derivatives could, in principle. 

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