Phthalocyanines, conductivity

Chemical and biological sensors (qv) are important appHcations of LB films. In field-effect devices, the tunneling current is a function of the dielectric constant of the organic film (85—90). For example, NO2, an electron acceptor, has been detected by a phthalocyanine (or a porphyrin) LB film. The mechanism of the reaction is a partial oxidation that introduces charge carriers into the film, thus changing its band gap and as a result, its dc-conductivity. Field-effect devices are very sensitive, but not selective. 

Phthalocyanines with side groups which can undergo Diels-Alder reactions can be synthesized as precursors for ladder polymers (see pp772, 773).344-345 For these kinds of compounds an intrinsic conductivity is predicted.346 Both dienophilic and enophilic phthalocyanines have been prepared. The possibility to undergo a Diels-Alder reaction was tested with fumaronitrile and 2,3-dimethylbutadiene.345 Via a Diels-Alder reaction, a connection between a phthalocyanine and [60]fullercne was also achieved.336... 

Intensive research on the electrocatalytic properties of polymer-modified electrodes has been going on for many years Until recently, most known coatings were redox polymers. Combining redox polymers with conducting polymers should, in principle, further improve the electrocatalytic activity of such systems, as the conducting polymers are, in addition, electron carriers and reservoirs. One possibility of intercalating electroactive redox centres in the conducting polymer is to incorporate redoxactive anions — which act as dopants — into the polymer. Most research has been done on PPy, doped with inter alia Co 96) RyQ- 297) (--q. and Fe-phthalocyanines 298,299) Co-porphyrines Evidently, in these... 

Coutanceau C, El Hourch A, Crouigneau P, Leger JM, Lamy C. 1995. Conducting polymer electrodes modified by metal tetrasulfonated phthalocyanines Preparation and electro-catalytic behaviour towards dioxygen reduction in acid medium. Electrochim Acta 40 2739-2748. 

Unique combinations of properties continue to be discovered in inorganic and organometallic macromolecules and serve to continue a high level of interest with regard to potential applications. Thus, Allcock describes his collaborative work with Shriver (p. 250) that led to ionically conducting polyphosphazene/salt complexes with the highest ambient temperature ionic conductivities known for polymer/salt electrolytes. Electronic conductivity is found via the partial oxidation of unusual phthalocyanine siloxanes (Marks, p. 224) which contain six-coordinate rather than the usual four-coordinate Si. 

These results illustrate that electrochemical techniques can be employed to synthesize a vast range of [Si(Pc)0]n-based molecular metals/conductive polymers with wide tunability in optical, magnetic, and electrical properties. Moreover, the structurally well-defined and well-ordered character of the polymer crystal structure offers the opportunity to explore structure/electro-chemical/collective properties and relationships to a depth not possible for most other conductive polymer systems. On a practical note, the present study helps to define those parameters crucial to the fabrication, from cheap, robust phthalocyanines, of efficient energy storage devices. 

The redox potentials of zinc-substituted phthalocyanines are shown to be linearly dependent on the total Hammett substituent constant.837 In 1987, Stillman and co-workers used the absorption and magnetic circular dichroism spectra of the zinc phthalocyanine and its 7r-cation-radical species to assign the observed bands on the basis of theoretical calculations. The neutral and oxidized zinc phthalocyanine complexes with cyanide, imidazole, and pyridine were used with the key factor in these studies the stability of the 7r-cation-radical species.838 The structure of zinc chloro(phthalocyaninato) has been determined and conductivity investigated.839... 

The reddish metal was already known in prehistoric times. It occasionally occurs as a native metal, but mostly in conspicuous green ores, from which it is extracted relatively easily. It is convenient to work, but not very hard. Not very optimal as a tool ("Otzi the Iceman" had a copper axe with him). Only through the addition of tin is the more useful bronze obtained. Its zinc alloy is the versatile and widely used brass. Copper is one of the coinage metals. Water pipes are commonly made of copper. Its very good thermal and electrical conductivity is commonly exploited (cable ), as well as its durability (roofs, gutters), as the verdigris (basic copper carbonate) protects the metal. Cu phthalocyanines are the most beautiful blue pigments. Seems to be essential to all life as a trace element. In some molluscs, Cu replaces Fe in the heme complex. A 70-kg human contains 72 mg. 

Favaro and Fiorani [34] used an electrode, prepared by doping conductive C cement with 5% cobalt phthalocyanine, in LC systems to detect the pharmaceutical thiols, captopril, thiopronine, and penicillamine. FIA determinations were performed with pH 2 phosphate buffer as the carrier stream (1 mL/min), an injection volume of 20 pL, and an applied potential of 0.6 V versus Ag/AgCl (stainless steel counter electrode). Calibration curves were developed for 5-100 pM of each analyte, and the dynamic linear range was up to approximately 20 pM. The detection limits were 76, 73, and 88 nM for captopril, thiopronine, and penicillamine, respectively. LC determinations were performed using a 5-pm Bio-Sil C18 HL 90-5S column (15 cm x 4.6 mm i.d.) with 1 mM sodium 1-octanesulfonate in 0.01 M phosphate buffer/acetonitrile as the mobile phase (1 mL/min) and gradient elution from 9 1 (held for 5 min) to 7 3 (held for 10 min) in 5 min. The working electrode was maintained at 0.6 V versus Ag/AgCl, and the injection volume was 20 pL. For thiopronine, penicillamine, and captopril, the retention times were 3.1, 5.0, and 11.3 min, and the detection limits were 0.71, 1.0, and 2.5 pM, respectively. 

Several metallophthalocyanines have been reported to be active toward the electroreduction of C02 in aqueous electrolyte especially when immobilized on an electrode surface.125-127 CoPc and, to a lesser extent, NiPc appear to be the most active phthalocyanine complexes in this respect. Several techniques have been used for their immobilization.128,129 In a typical experiment, controlled potential electrolysis conducted with such modified electrodes at —1.0 vs. SCE (pH 5) leads to CO as the major reduction product (rj = 60%) besides H2, although another study indicates that HCOO is mainly obtained.129 It has been more recently shown that the reduction selectivity is improved when the CoPc is incorporated in a polyvinyl pyridine membrane (ratio of CO to H2 around 6 at pH 5). This was ascribed to the nature of the membrane which is coordinative and weakly basic. The microenvironment around CoPc provided by partially protonated pyridine species was suggested to be important.130,131 The mechanism of C02 reduction on CoPc is thought to involve the initial formation of a hydride derivative followed by its reduction associated with the insertion of C02.128... 

Abstract In this chapter, recent progress in the synthesis, crystal structures and physical properties of monomeric phthalocyanines (Pcs) is summarized and analysed. The strategies for synthesis and modification of Pcs include axial coordination of central metal ions, peripheral substitution of Pc rings and the ionization of Pcs. The crystal structures of various typical Pcs, especially the effects of different synthetic and modification strategies on the supramolecular assemblies of Pcs via %—% interactions between Pc rings, are discussed in detail. Finally, the UV-vis spectroscopic, conducting, magnetic and catalytic properties of some Pcs with crystal structures are presented briefly, and the correlations between various properties and the molecular structure discussed. 

Phthalocyanine-based molecular metals and conductive polymers have been prepared and investigated by 13C solid state NMR. Among others, Ge serves as a central atom219,220. However, no discussion of a special role of the metal is presented in this work. 

The use of electrochemical methods for the destruction of aromatic organo-chlorine wastes has been reviewed [157]. Rusling, Zhang and associates [166, 167] have examined a stable, conductive, bicontinuous surfactant/soil/water microemulsion as a medium for the catalytic reduction of different pollutants. In soils contaminated with Arochlor 1260, 94% dechlorination was achieved by [Zn(pc)] (H2pc=phthalocyanine) as a mediator with a current efficiency of 50% during a 12-h electrolysis. Conductive microemulsions have also been employed for the destruction of aliphatic halides and DDT in the presence of [Co(bpy)3]2+ (bpy=2,2 -bipyridine) [168] or metal phthalocyanine tetrasulfonates [169]. 

Fig. 1. Cyclic voltammetry of 7% w/w iron phthalocyanine, FePc dispersed on Vulcan XC-72 carbon, after a heat treatment at 280°C in a flowing inert atmosphere. The measurement was conducted with the material in the form a thin porous Teflon bonded coating in 1 M NaOH at 25°. Sweep rate 5 mV/s. (Reproduced with permission from ref. 3. Copyright 1985 Elsevier.)...

An important area of research in silicon phthalocyanine chemistry has been the preparation of conducting polymers through Si—O—Si links.In one recent example, silicon phthalocyanine complexes have been appended to a den-drimer framework through Si—O—C(triazine) bonds formed by reaction of the salt Na [Si(Pc)(Ph)0 ] with a dichlorotriazine derivative. 

Transition metal compounds, such as organic macrocycles, are known to be good electrocatalysts for oxygen reduction. Furthermore, they are inactive for alcohol oxidation. Different phthalocyanines and porphyrins of iron and cobalt were thus dispersed in an electron-conducting polymer (polyaniline, polypyrrole) acting as a conducting matrix, either in the form of a tetrasulfonated counter anion or linked to... 

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