Conjugation electrically active polymers

There is another type of electrically active polymer that is known as the electroconductive polymer, in which polymer chains contain long conjugated double bonds, and this chemical structure adds electroconductive properties to the polymers. In these cases, the electrically induced deformation is considered to have originated from the electrochemical reactions such as the oxidation and reduction of the polymer chain. For the deformation, some additives such as dopants have been known to be necessary for effective actuation. Therefore, the electrical actuation of these materials has been... 

Conjugated polymers, including optically active polymers and dendronized polymers that are very useful in electrical and optical fields and asymmetric catalysis, will continue to attract interest from chemists and materials scientists. It is well anticipated that more and more polymers with interesting structures and properties will be synthesized from the transition metal coupling strategy. 

Fig. 2.11. Three organic semiconducting polymers, (a) Polypyrrole, (b) plythipo-hene, and (c) poly(3,4-ethylenedioxythiophene) (PEDOT). All three have an sp conjugated backbone identical to polyacetylene. It is along the pi-bonds in this backbone that these materials exhibit carrier delocalization and electrical activity.

In the optical and electrical activity of conjugated polymers several phenomena occur ... 

It was also observed that conjugated polymers that are also electrical conductors (see Chap. 10) exhibit optical activity that depends critically on their structural organization [78]. Thus, strong chiroptical properties can be obtained firom substituted polythiophene [79] (Chap. 10) with optically active side chains, especially when the monomers are coupled within the polymer in a regioregular head-to-tail fashion. Actually, optical activity of these materials is only found when the polymers are aggregated at low temperature, in poor solvent, or in solution cast films. This contrasts with other optically active polymers, like polypeptides, poly(l-alkynes) and polyisocyanates that show an optically active conformation of the main chain in the absence of supramolecular association. 

Most of the reported conjugated polymers with nonlinear optical or electrical activities are carbon-carbon conjugated systems, such as the extensively studied polyenes (e.g., polyacetylenes [15], polydiacetylenes [16,17], poly-/ -phenylenes) and heteroaromatic polymers (e.g., polypyrroles, polythiophenes, polycarbazoles, polyanilines) [18]. The synthetic methods, applications, and the structure-property relationships of these polymers have also been substantially investigated [19-21]. 

Side-chain substitutions are now routinely used to enhance solvent solubility and fusibility so that various conventional polymer processing methods may be used. Some of these polymeric materials, e.g., the poly(3-al-kylthiophenes), may contain only a small volume fraction of electrically active regions (i.e., the 7r-conjugated main chain). Still these materials can exhibit extremely high dc conductivities (7) after doping (or more precisely, intercalation) by a guest species. This intercala-... 

Multiple Heck reactions have also been applied in a number of ways to prepare polymers (Scheme 40). One-dimensionally 7r-conjugated polymers are attractive materials because of their optical and electrical properties resulting from 7r-electron delocalization along their main chains. Among these, poly(p-phenylenevinylene) (PPV) shows high electrical conductivity, large non-linear optical responses, and electroluminescent activity. One approach... 

Of much interest are the electroluminescence properties of conjugated polymers that allow the development of electrically switched light-emitting devices [8.257]. Electric field activated bistable molecules are expected to switch at a critical field strength [8.258]. 

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