Doped polyacetylene, energy levels

Using this model, the doping of polyacetylene proceeds by the interaction of dopants with solitons initially present in the polymer, then by polaron formation and at even higher doping levels by soliton formation. The soliton states then broaden into a soliton band that eventually fills the gap, giving a continuum of energy levels and a metallic state. 

In polythiophene and in the substituted polythiophenes, polarons were identified [135-137]. The data was analyzed using the amplitude mode and phase mode model, yielding an approximate value of 0.3 for the pinning parameter, for both the photoinduced and doping induced polarons (the IRAV appear at nearly the same frequencies). The larger pinning, relative to polyacetylene, is possibly related to the different electronic energy level structure of the polarons. 

Polyacetylene, becomes ionized after doping if the dopants are electron acceptors, or it receives extra electrons if the dopant represents an electron donor (symbolized by D+ in Fig. 9.12). The perfect polyacetylene exhibits the bond alternation discussed above, but it may be that we have a defect that is associated with a region of changing rhythm" (or phase ) from (— — = — =) to (— = — = —). Such a kink is sometimes described as a soliton wave (Fig. 9.12a,b) i.e., a solitary wave first observed in the 19th century in Scotland on a water channel, where it preserved its shape while moving over a distance of several kilometers. The soliton defects cause some new energy levels ( solitonic le >els ) to appear within the gap. These levels too form their own solitonic band. 

---