Polyacetylene degenerate ground state

Figure 4-2. Total energy as a function of a structural deformation coordinate. (a) 7Van5-polyacetylene (degenerate ground-state system) (b) poly( p-phenylene) nondegenerate ground-state system).

Polyacetylene is a polymer which has a degenerate ground state it possesses two geometric structures having exactly the same energy and differing only in the sequence of the carbon-carbon single and double bonds (Fig. 9.6). 

T. Kobayashi In the same context, I would like to point out that, in polymer systems with degenerate ground states such as trans-polyacetylene, it may occur that a fraction of the excited species (exciton) is split into a soliton and an antisoliton with opposite charges. These can be bound by Coulombic interaction and also by steric hindrance. 

In contrast to polyacetylene, the other CPs shown in Scheme 1 have non-degenerate ground states (i.e. they do not possess two equivalent resonance forms), and thus, do not show evidence of soliton formation. In this instance, the oxidation of the CP is believed to result in the destabilization (raising of the energy) of the orbital from which the electron is removed. This orbital s energy is... 

The other isomer is called cis-polyacetylene. This has a slightly different structure with non-degenerate ground state energy. 

The equivalent names from chemistry and physics for the excitations of conducting polymers are summarized in Table VA-1. We use as model systems frans-polyacetylene for the degenerate ground state polymer and polyfpara-phenylene) for the non-degenerate ground state polymer. 

From the viewpoint of its molecular structure, PPV can be considered an alternating copolymer of the repeat units of polyacetylene and poly(p<7r<7-phenylene) (Figure 1.35). With respect to electronic structure, it is one of the simplest non-degenerate ground state polymers, and as such it is attractive for theoretical approaches. 

This polymer can be considered a derivative of trans-polyacetylene (Figure 1,60) it has also been prepared with a Shirakawa catalyst. The electronic structure has a degenerate ground state, but there are three inequivalent positions for solitons on the backbone, Gibson et al. [356] have reported the polymer to be x-ray amorphous, in contrast to tran5-polyacetylene, and to be even more air-sensitive than the latter. Doping is feasible with acceptors such as I2 and AsFs, to a maximum conductivity of 1 S cm . ... 

Contrary to the case of trons-polyacetylene with a degenerate ground-state structure, most other conju-... 

FIGURE 5.19 (a) and (b) Degenerate ground state of tra s-polyacetylene. (c) Polyacetylene chain with a defect... 

Solitons are neutral defects which arise as a consequence of the degenerate ground state structure of tmns-polyacetylene. J/ans-polyacetylene has a conjugated carbon backbone as shown in Figure 1. Each carbon is sp2 hybridized forming bonds with two adjacent carbons and one hydrogen. The pz orbitals lie perpendicular to the polymer chains and... 

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