Dopant-chain interaction

Yamashiro and co-workers have estimated the dopant-chain interaction and its role in interchain transfer [82]. They showed that the dopants mediate the largest interchain transfer of about 0.3-0.1 eV with five to seven carbon atoms in another chain that is in contact with a common dopant column. The interchain transfer via dopants has little effect on interchain states but yields a modification of the orbital energy spectrum. 

The strategy used to suppress thermal undoping is to avoid the side-chain interactions by separating the side-chains from one another, or from the main chains, while maintaining enough space around the main chain for the dopants. Thermochromism and solvatochromism exhibited by these materials are also related to side-chain mobility [27,81]. 

This aspect of polymer-dopant interaction has been the subject of a more detailed study by Chen et al. [104]. PPV-Cs has been compared with rubidium-doped polyacetylene, for which the guest/host size ratio is very nearly the same (Table 1.7). Whereas poly-acetylene-Rb has an intrachannel coherence length of 25 A for the ion sublattice, the coiresponding value is 70 A in the case of PPV-Cs the ion siiblattices are incommensurate for both at the compositions studied. Such intriguing differences can only be understood by considering, in a more polymer-specific manner, the character of the chain and the guest-host interactions. 

With the possible exception of lithium, which may interact chemically with organic chains, the small sizes of alkali metal n-dopants and high charge concentration compared with those of common p-dopants (IJ, FeCl4, AsF, etc.) favor the... 

Simulations reveal structural interactions between the migrating dopant ion and the host lattice in which polymer chains respond to the migrant by distorting from planarity. As would be expected, this interaction increases rapidly with the flexibility of the chains. In Section 6.2 we see that in nonconjugated polymers (i.e., those with no n electronic component to favor chain planarity), the host dopant interaction plays an essential role in the jump mechanism in migration. 

Static lattice simulation methods predict the tendency of polymers to avoid the strict regularity of a crystal by finding several lattice structures with similar energies but that vary in their chain-setting angle and cell vectors. The readiness with which the polymer sublattice in doped systems lowers its symmetry is echoed in both the defective static lattice simulations and the molecular dynamics treatment of lattice motions. In the former we observed the wide ranging response of the chains to even a small displacement of a dopant ion as described in Sections 5.3.2, 5.3.4, 5.4.2. and 5.6.3 while the dopant s power spectrum calculated in the course of the MD lattice simulations in Section 6.1 testifies to the important host-dopant interactions in potassium-doped polyacetylene. 

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