Polyacetylene transition energies

Extensive electron delocalization along the chain direction leads to an electronic transition energy for one-photon absorption (E0) of typically 15 000-16 000 cm-l for an unstrained backbone (.7). This value is very close to that of polyacetylene (or... 

The physical parameter range relevant for trans-polyacetylene, namely Coulomb interactions comparable to the bandwidth, is intermediate between the weak and strong coupling limits defined in Chapter 5. As shown in Fig. 5.2, this means (as already discussed) that the and 2 A+ vertical transition energies are... 

Fig. 4.2 A short segment of t rans -polyacetylene is shown with an abrupt (idealized) reversal of the bond alternation pattern (see text). Top- a neutral soliton with an unpaired spin and an energy state near the middle of the electron energy gap. Middle the addition of an electron results in the formation of a spinless negatively charged soliton. Bottom the extraction of an electron from the top results in the formation of a spinless positive soliton. The optical transitions associated with the charged solitons are indicated as arrows on the right.

For long (infinite) trani -polyacetylene chains, the treatment of quantum lattice fluctuations is very complicated, because many lattice degrees of freedom couple in a non-linear way to the lowest electronic transitions. We have recently shown that for chains of up to 70 CH units, the amount of relevant lattice degrees of freedom reduces to only one or two, which makes it possible to calculate the low-energy part of the absorption spectmm in an essentially exact way [68]. It remains a challenge to study models in which both disorder and the lattice quantum dynamics are considered. 

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