Ferrocene doping

Ferrocene doping provides an electrochemical probe of the material during gelation, reporting in particular on the mobility of the probe as measured by the diffusion coefficient.133,134 If necessary the sol-gel material can be loaded with carbon powder to confer electrical conductivity (composite ceramic carbon electrodes, CCEs).135 Single-walled nanotubes in vanadia aerogels exhibit high capacities for lithium intercalation.136... 

Fig. 9.32 (a) Time evolution of the SRPAC signal (in log scale) for several temperatures obtained from the molecular glass former DBP doped with Fe-enriched ferrocene, (b) The relaxation rate X (in log scale) as a function of inverse temperature 1,000 obtained from analyzing the SRPAC... 

Third, metallocene units, such as ferrocene or ruthenocene, have been linked to phosphazene cyclic trimers or tetramers and these were polymerized and substituted to give polymers of the type mentioned previously (41). Polyphosphazenes with ferrocenyl groups can be doped with iodine to form weak semiconductors. Polymer chains that bear both ruthenocenyl and ferrocenyl side groups are prospective electrode mediator systems. 

Scheme VI. Representation of the interface energetics for intrinsic a-Si H at short circuit, dark equilibrium with ferricenium/ferrocene in EtOH, electrolyte solution (left) and under illumination with 632.8-nm light with a load in series in the external circuit (right). The diagrams are adapted from data in Reference 65 for intrinsic a-Si H (1-4-fi thick) on stainless steel first coated with heavily n-doped a-Si H (200-A thick) to ensure an ohmic contact near the bottom of the conduction band. In typical experiments Eredox = 0.4 V vs. SCE.

Figure 2. Band edge positions obtained over a period of three weeks for p-and n-type WSe2 -CH3CN interfaces containing metallocene redox couples (ferrocene, FER decamethylferrocene, DFER and acetylferrocene, AFER) each at three concentrations (preceding letter refers to high.H medium,M and low, L). Two different electrodes were used to obtain the data for n-WSe2 with doping densities between 1016 -1017 cm-3.

Electrochemical doping of insulating polymers has been attempted for polyacetylene, polypyrrole, poly-A/-vinyl carbazole and phthalocyaninato-poly-siloxane. Significantly, Shirota et al. [91] claim to have achieved the first synthesis of electrically conducting poly(vinyl ferrocene) by the method of electrochemical deposition (ECD) [91]. This is based on the insolubilization of doped polymers from a solution of neutral polymers. A typical procedure applied [91] for polyvinyl ferrocene is to dissolve the polymer in dichlorometh-ane and oxidize it anodically with Ag/Ag+ reference electrode under selective conditions. The modified polymer [91] (Fig. 28) is a partially oxidized mixed valence salt containing ferrocene and ferrocenium ion pendant groups with C104 as the counter anion. 

Sodium phosphate monobasic [S 9638], sodium phosphate dibasic [S 0876], sodium chloride [S 7653], acetylcholinesterase from Elect-rophorus electricus (Type V-S) [C 2888], potassium chloride [P 3911], 1,2-diaminobenzenedihydrochloride [P 1526], paraoxon (o,o-diethyl o-4-nitrophenyl phosphate) [D 9286], ferrocene carboxylic acid [106887], aniline [A 9880] and acetylthiocholine chloride [A 5751] were purchased from the Sigma Chemical Company (Dorset, UK). Screen-printed transducers were purchased from Gwent Electronic Materials Ltd. (Gwent, Wales, UK). These electrode assemblies comprised a working electrode based on carbon ink doped with cobalt phthalocya-nine, an on board reference electrode (Ag/AgCl) and counter electrode (platinum) (see Fig. 24.1). 

In addition to doping with fullerenes, SWCNTs can also be filled with molecules such as ferrocene, chromocene, ruthenocene, vanadocene and tungsteno-cene dihydride. The filling with metallocenes occurred from the vapor phase with formation of collinear metallocene chains inside the nanotubes [268], Also the filling with Zn diphenylporphyrin was successful and established from absorption spectra and Raman measurements [269]. 

Perhaps the original hope for these polymers was that they would act simultaneously as immobilisation matrix and mediator, facilitating electron transfer between the enzyme and electrode and eliminating the need for either O2 or an additional redox mediator. This did not appear to be the case for polypyrrole, and in fact while a copolymer of pyrrole and a ferrocene modified pyrrole did achieve the mediation (43), the response suggested that far from enhancing the charge transport, the polypyrrole acted as an inert diffusion barrier. Since these early reports, other mediator doped polypyrroles have been reported (44t45) and curiosity about the actual role of polypyrrole or any other electrochemically deposited polymer, has lead to many studies more concerned with the kinetics of the enzyme linked reactions and the film transport properties, than with the achievement of a real biosensor. 

For electrochemical detection, the particles used are composed of doped silica (Co(bpy)33+ as the doping agent) [35], iron/gold [36], polystyrene beads internally loaded with electroactive markers (ferrocene) [37] or gold [38],... 

Plenio and co-workers synthesized and polymerized of l-iodo-2-methoxymethyl-3-ethynylferrocene and l-iodo-2-(A,lV-dimethylamino methyl)-3-ethynylferrocene to give 1,3-linked ferrocene-acetylene polymers.176,177 These polymers were synthesized by Sonogahira coupling reactions. These polymers showed optical activity176 or possessed functionalized side chains.177,178 Scheme 2.28 shows the reaction of diiodoferrocenes with diethynyl monomers.178,179 The palladium-catalyzed reactions led to polymers 93a,b, which when doped with iodine displayed semiconducting properties. The iodine-oxidized polymer 93a displayed an electrical conductivity of 1.3 X 10 4S/cm. 

Photoactive Additives.—Ferric compounds, in particular, the chloride, continue to attract much interest as photosensitizers for thermoplastics. " From e.s.r. work the mechanism appears to involve a redox reaction resulting in the formation of active hydroxy-radicals. Photodegradable polyethylene film has been developed by doping it with radiation-modified atactic polypropylene and hydroxyethyl-ferrocene. Several workers have studied the dye-sensitized photo-oxidation of polyisoprene and di-n-butyl sulphide embedded in Augustyniak and... 

Polyferrocenylene exhibits significant electrical conductivity when doped (see Section 12.06.3.2.1) and, thus, the introduction of ferrocene units into the main chain of polymers with cr-, ct-tt-, or 7r-conjugation in the backbone is a potentially appealing research objective. Studies of materials with short spacers were provided in Section 12.06.3 here we focus on polymers with spacers longer than three atoms. 

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