Polymer Cation-Radical Salts

Fi. 3b. Proposed packing of polymer cation-radical salts [(segment) 2... 

Tens of conductive LB films have been developed so far, including metallic and superconductive LB films. These LB films are classified into the categories anion radical salt, charge-transfer complex, cation radical salt, conducting polymer, and transition metal complex in this section. The LB films, with metallic temperature dependences of conductivity, and the fullerene LB films, which exhibit a superconducting transition, are discussed separately. 

M. Monkenbusch, W. Muller, and J. Eiffler for their permission to report on parts of their yet unpublished work or from their theses. The work reported from the authors laboratory was supported by a grant from the Stiftung Volkswagenwerk (cation radical salts) and by a grant from the BMFT (conducting polymers). 

Poly-SchifF bases containing DCZB units in the main chain (26b) were synthesized by the direct polycondensation of rran5-l,2-bis(3-formyl-9-carbazolyl)cyclo-butane with aromatic diamines [217]. Complexation of the polymers (26b) with iodine produces cation-radical salts which result from an electron transfer from DCZB moieties to iodine. The undoped polymers are insula-... 

This chapter is composed of 12 main sections. At first the LB technique and strategy towards the conductive LB films are briefly summarised. Secondly, the LB films of molecular conductors so far reported are presented in four sections anion radical salts, cation radical salts, charge-transfer complexes and transition metal complexes. The progress in conductive-polymer LB films will be also mentioned briefly. These sections will provide the reader with a sense of the present situation and future possibilities in this field. Thirdly, special topics on metallic conductivity and switching phenomena in LB films will be described. 

An important point is that the electrochemically driven charge transport in these polymeric materials is not dependent on the presence of mixed valence interactions which are well known to give rise to electronic conductivity — in a number of cation radical crystalline salts. This is clearly seen from the absorption spectrum of the electrochemically oxidized pyrazoline films (Figure 8) which show no evidence for the mixed valence states that are the structural electronic prerequisites for electrical conductivity in the crystalline salts. A more definitive confirmation of this point is provided by the absorption spectrum (Figure 10) of electrochemically oxidized TTF polymer films which shows... 

At least in some cases, a low Eox facilitates the generation and/or injection of a positive charge carrier from the CGL (see above). A low qx also makes it unlikely that an impurity might have a much lower value and act as a trap for holes [44h. For obvious reasons, the cation radicals of these compounds must be stable in the CTL environment, and some of the better donors indeed form remarkably stable radical-ion salts, even in fluid solution [44a]. The CTM must be highly soluble in the polymeric host and the solvent used to fabricate the CTM. It must provide a high concentration of electrically active moieties without plasticizing the host polymer excessively. Compounds that meet these requirements are typically rather large and flexible, and they may contain more than one electrically independent moiety per molecule, e.g., 1,1-bis(di-4-tolylaminophenyl)cyclohexane (TAPC) in Scheme 2. 

An interesting bridge between charge transfer salts and conducting polymers was suggested by Miller et al. [868]. They investigated a substituted terthiophene cation radical that forms tt stacks, which show electric conductivity without being a true polymer. 

To the more usual homolytic fragmentation of aryl halides (from the excited state or from the radical anion, the well known SrnI reaction, for a recent example see the arylation of aromatics), the heterolytic version of the reaction which produces phenyl cations has more recently joined. A theroretic study on the photodissociation of fluorinated iodobenzenes has been published. The perfluoroallgrlation of various alkenes has been obtained by irradiation in the presence of iodoperfluorobutane. The formation of phenyl cations is exemplified in many arylation reactions and, in the case of o-chlorostannane, also a benzyne has been reported. In the field of polymer chemistry, iodonium salts are model cationic photoinitiators. In particular the truxene-acridine/diphenyl iodonium salt/9-vinylcarbazole combination is able to promote the ringopening polymerization of an epoxide, whereas the truxene AD/allq l halide/amine system is very efficient in initiating the radical photopolymerization of an acrylate. ... 

Further confirmation for the above mechanism was obtained by direct spectroscopic observation of the perylene cation-radical when perylene was employed as a photosensitizer for these photoinitiators as well as detection of perylene end groups bound to the polymers produced by these systems It is interesting to note that while the direct photolysis of dialkylphencylsulfonium salts is a reversible process, the photosensitized photolysis is an irreversible one. Consequently, in contrast to the direct photolysis, photosensitized photolysis in an inert solvent followed by addition of a monomer results in spontaneous dark polymerization. 

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