Polymer-dopant system

Bredas JL, Chance RR, et al., "Structural Basis for Semi-conducting and Metallic Polymer [Dopant Systems", Chemical Reviews 82 (1982) 209. 

These results may well be typical of most polymer/dopant systems. Certainly the behavior of these systems with respect to triplet exciton migration seems quite similar in spite of their rather distinctive molecular architecture. Let us now turn to an examination of systems in which chromophore units are regularly arranged by virtue of their being bonded to the backbone of a polymer chain. In this way, it may be possible to assess the effects of chromophore organization on the mechanism of triplet exciton migration and decay. 

In order to demonstrate this effect to best advantage it was necessary to choose a PVCA sample having a relatively low molecular weight. In this way Interference of the phosphorescence emission by delayed fluorescence is minimized. These are provacative results because they indicate that there may be no well defined lowest triplet state in vinyl aromatic polymers unless special steric or electronic effects are present which nullify inter-chromophore interactions. On the other hand, they may provide an additional tool with which to investigate rates of energy migration in polymers and in some polymer/dopant systems as well. 

A model has been proposed by us for this behaviour in which the compensation of a polymer-dopant system occurs in four stages. In the first stage, the counter-ion present in the outer monolayer of the polymer-dopant system, is compensated. This is a very fast ionic reaction without any potential barrier to overcome because diffusion is not involved. The monolayer becomes an insulator instantaneously but its thickness is negligible compared to the film thickness and the conductivity loss would be very small at this stage. In the second stage, the affected monolayer skin expands into the polymer-dopant system from both sides, at a rate controlled by the diflusion of compensant which may further be influenced by the rate of chemical... 

R. H. Baughman, J. L. Bredas, R. R. Chance, R. L. Elsenbaumer, L. W. Shacklette, Structural basis for semiconducting and metallic polymer dopant systems, Chemical Reviews 1982, 82, 209. 

Similar information can be also obtained by the ESR linewidth as a function of temperature, dominated by the Elliott mechanism through the spin-orbit coupling. It could possibly yield temperature dependence of the electrical resistivity if it were analyzed together with the g-shift and/or g-shift anisotropy and the spin dynamics data. It is noteworthy that a variety of temperature dependences are uniformly understandable with a single formulation characteristic of one-dimensional electronic systems. This mechanism is observable only in polymers with heavy nuclei, such as alkali and sulphur. It is also worth noting that the dopant nuclei could contribute to the Elliott mechanism in the donor dopant systems. Contrary to this, nuclei in the acceptor dopants could contribute little, Such a difference reflects each electronic state. Further investigation makes clear these points. 

The search for easy-to-manufacture, highly stable compounds with a known number of double bonds also focused on perylene derivatives. Further investigation led to the concept of ribbon-like polymers (e.g. by repetitive Diels-Alder addition [12]) and ladder-like self-dopant systems [13]. 

The layered guest-host structures that can also develop undergo a structural evolution more reminiscent of the intercalation process in 2D layered materials (e.g., graphites or silicates). In this case, quasi-2D galleries open up between stacked sheets of the polymers chain as shown in Fig. 25.8. This type of ordering has often been reported in structural studies [84-89] using molecular dopants. Systems showing evidence of layered structures include iodine-doped PA [86] and AsF.s-doped PPV [87]. These layered structures may occur either alone or in combination with channel formations [85,89]. 

Significant variations in the properties of polypyrrole [30604-81-0] ate controlled by the electrolyte used in the polymerization. Monoanionic, multianionic, and polyelectrolyte dopants have been studied extensively (61—67). Properties can also be controlled by polymerization of substituted pyrrole monomers, with substitution being at either the 3 position (5) (68—71) or on the nitrogen (6) (72—75). An interesting approach has been to substitute the monomer with a group terminated by an ion, which can then act as the dopant in the oxidized form of the polymer forming a so-called self-doped system such as the one shown in (7) (76—80). 

Conducting polymer composites have also been formed by co-electrodeposition of matrix polymer during electrochemical polymerization. Because both components of the composite are deposited simultaneously, a homogenous film is obtained. This technique has been utilized for both neutral thermoplastics such as poly(vinyl chloride) (159), as well as for a large variety of polyelectrolytes (64—68, 159—165). When the matrix polymer is a polyelectrolyte, it serves as the dopant species for the conducting polymer, so there is an intimate mixing of the polymer chains and the system can be appropriately termed a molecular composite. 

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... 

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