Poly-p-phenylene cations

For instance, poly-p-phenylenes in their doped states manifest high electric conductivity (Shacklette et al. 1980). Banerjee et al. (2007) isolated the hexachloroantimonate of 4" -di(tert-butyl)-p-quaterphenyl cation-radical and studied its x-ray crystal structure. In this cation-radical, 0.8 part of spin density falls to the share of the two central phenyl rings, whereas the two terminal phenyl rings bear only 0.2 part of spin density. Consequently, there is some quinoidal stabilization of the cationic charge or polaron, which is responsible for the high conductivity. As it follows from the theoretical consideration by Bredas et al. (1982), the electronic structure of a lithium-doped quaterphenyl anion-radical also differs in a similar quinoidal distortion. With respect to conformational transition, this means less freedom for rotation of the rings in the ion-radicals of quaterphenyl. This effect was also observed for poly-p-phenylene cation-radical (Sun et al. 2007) and anion-radical of quaterphenyl p-quinone whose C—O bonds were screened by o,o-tert-hutyl groups (Nelsen et al. 2007). 

ABSTRACT Resonance Raman spectroscopy has been demonstrated to give important structural information on the reactions of aromatic molecules in the interlayer of transition-metal ion-exchanged montmorillonites. Para-substituted benzenes or 4,4 -substituted biphenyls are oxidized to form their cation radicals, which are stabilized in the interlayer of the clay mineral. The oxidative dimerization or polymerization results in the formation of biphenyl type cations and poly-p-phenylene cations from mono-substituted benzenes and benzene, respectively. 

Biphenyl and p-terphenyl react similarly to form poly-p-phenylene cation, although the adsorbed amounts are less compared with that of benzene,... 

Fig. 2 Schematic representation of the doping of poly(p-phenylene ethynylene) (PPE) under formation of polarons (radical cations, radical anions) and bipolarons (dications, dianions). Note that multiple carriers can coexist on each macromolecule...

Radical-Cation Salts as Models for Conducting Polymers. Polymers that have an extended Tr-electron system in their backbones, for example, polyacetylene (PA) and poly(p-phenylene) (PPP), can be transformed by oxidation or reduction in the solid state (doping) to derivatives that exhibit metallike conductivity (24, 25). These materials are usually insoluble and infusible and exhibit a very complicated morphology that cannot be changed by subsequent treatment. The lack of knowledge about the structure and state of order is the cause of the current controversy about the conduction mechanism in doped polymers. 

Cross-coupling reactions were carried out in direct aqueous miniemulsions with 1,2,4-tribromobenzene as crosslinker, and Pd as catalyst [147], in order to obtain aqueous latexes of crosslinked poly(p-phenylene ethynylene) with good optoelectronic properties. The Glaser couphng reaction was also used to synthesize fluorescent conjugated particles of poly(arylene diethynylenes) in direct miniemulsions [148]. For this, 4,4 -dinonyl-2,2 -bipyridine was found to be a suitable ligand for solubilizing the copper (I) chloride catalyst in the toluene droplets. In this case, a solution of the monomers in toluene was first mixed with the solution of the catalyst, and the resultant mixture then miniemulsified in an aqueous solution of cationic surfactant. 

Zhu C, Yang Q, Liu L, Lv F, Li S, Yang G, et al. Multifunctional cationic poly(p-phenylene vinylene) polyelectrolytes for selective recognition, imaging, and killing of bacteria over mammalian cells. Adv Mater 2011 23(41) 4805-10. 

G. Brodowski, A. Horvath, M. Ballauff, M. Rehahn, Synthesis and intrinsic viscosity in salt free solution of a stiff chain cationic poly(p-phenylene) polyelectrolyte, Macromolecules 1996, 29, 6962. 

Poly(p-phenylene) was made by electrochemical polymerization in o/w microemulsions [49] of benzene, sulfuric acid, and anionic, cationic, or neutral surfactant. Benzene radical cation was stabilized by the anionic surfactant, resulting in polymer with less cross-linking, smaller particle size, and a relatively narrow size distribution. With cationic surfactants, the radical cation destabilized the water droplets and led to a broader size distribution of polymer particles. 

The polymerization reaction probably follows a mechanism similar to that proposed by Hsing et al. for the oxidative polymerization of benzene to poly(p-phenylene) [19]. Thus the reaction would be initiated by the cationic radical C4NH5 , which coordinates with other pyrrole units. The transition metal ion, being... 

Figure 14.17 Structures of frans-polyacetylene and poly(p-phenylene) showing reactions of two poiarons (radicai cations) to produce a bipoiaron (dication) (55).

Another view has recently been proposed by Wegner.Naphthalene and other simple aromarics can be oxidize electrochemi-cally to form monomelic radial cat n salts (Ar. X ) which have conductivities of 10 to 10 s/cm. The crystal structures of these reveal that the aromatic moieties form stacks, along which the charges and the electrons are presumably delocalized. The structure is formally analogous to that deduced for oxidized (doped) polyacetylene in which the polyene chains are arranged in stacks. This leads to the idea that intermolecular delocalization is the important feature which leads to high conductivity. Other data are consistent with this rationale. Biphenyl and terphenyl radical cation salts have crystal structures very similar to that of oxidized (doped) poly(p-phenylene lO). In the older literature oligoanilines (26) are reported upon iodine treatment to yield conductivities up to 1 s/cm the aniline moieties are stacked in these materials as well. Poly(N-vinyl-carbazole) (27) forms radical cation structures by oxidation with... 

In a series of papers these authors described the preparation, structure and electronic behaviour of a series of cation-radical salts of oligomeric poly(p-phenylene amine)s (PPA) of the general formula. 

Figure 11.6 The conjugated polymer poly(p-phenylene) A can be oxidized (p-doped) to a radical cation (positive polaron) B or a dication (positive bipolaron) C. The charged excitations are localized along the polymer chain, but may be forced to move when driven by an electric field. If the polymer is reduced (n-doped) instead of oxidized, negatively charged states are generated, viz., radical anions (negative polarons) and dianions (negative bipolarons).

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