Conjugation effects, polyacetylenes

The electrochemical properties of conductive polymer systems are important with regard to understanding the electrochemical doping process and in applications of conductive polymers as battery electrodes. We have developed a computational method, based on the Valence Effective Hamiltonian technique, which is remarkably effective in the computation of oxidation and reduction potentials of a variety of conjugated polymers (polyacetylene, polyphenylene, polythiophene, polypyrrole) and their oligomers. 

Since the discovery of doped polyacetylene, a range of polymer-intense semiconductor devices have been studied including normal transistors and field-effect transistors (FETs), and photodiodes and light-emitting diodes (LEDs). Like conductive polymers, these materials obtain their properties due to their electronic nature, specifically the presence of conjugated pi-bonding systems. 

Unlike polyacetylene, substituted polyacetylenes are amorphous, electrically insulator soluble polymers.413 They are highly stable and not sensitive to oxidation. Since the substituents exert a strong steric effect, the polyene backbone is not copla-nar, and as a result, only limited conjugation is possible. 

An extensive review of the synthesis of rc-conjugated polymers is presented using a tutorial approach to provide an introduction to the field intended for the undergraduate student and the experienced chemist alike. The many synthetic methodologies that have been used for the synthesis of conjugated polymers are outlined for each class of polymers with a focus on research from the 1990s. The effect of structure on electrical properties is detailed. Specific systems reviewed include the polyacetylenes, polyanilines, polypyrroles, polythiophenes, poly(arylene vinylenes), and polyphenylenes. 

Extensive ir-conjugation is also often associated with enhanced conductivity in organic systems (6). Polyacetylene and polythiophene which in the doped state exhibit very high electrical conductivity also exhibit relative large third-order nonlinear optical effects in... 

We choose as model system the simplest conjugated polymers - the trans-polyacetylene. This compound shows a. dimerized structure with an altemance between double bond (1.35A) and single bond (1.45A) the monomer is then simply a double bond (see figure (8)). The tt electrons are assumed to be effectively describe not by the full PPP Hamiltonian but by the Extended Peierls-Hubbardmodel (EPH) [17, 14], a short version of it) for simplicity... 

Similarly, cubic effects such as four-wave mixing, phase conjugation, and optical bistability form the basis of optical functions of strategic importance. In this case, materials such as polyacetylene could, in principle, compete effectively with inorganic solids such as gallium arsenide. 

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