Modern Polymer Spect..

Figure 4-16. Schematic structures of polythiophene chains doped with electron acceptors (dopant
content, 25 mole'% per thiophene ring) and bonding electronic levels of positive polarons and
bipolarons. (a1 Polaron lattice: (bi bipolaron lattice. A. acceptor: +. positive charge; -, negative
charge; 0, electron; -, electronic energy level.
Ferrni level .-..
-.... Ferrni level
Figure 4-17. Schematic band structures of
dn infinite polymer chain doped with
acceptors (dopant content, 25 mole%) per
thiophene ring). (a) Polaron lattice;
(b) bipolaron lattice Shadowed areas are
(a) (b) filled with electrons [ 1261.
can be explained as follows. Although a single chain itself behaves like a metal,
macroscopic electrical conduction is limited by interchain, interdomain, or interfibril
charge transport. Here, we will discuss the intrachain metallic charge transport.
Let us suppose an infinite nondegenerate polymer chain (e.g., polythiophene)
doped heavily with electron acceptors. At a high dopant content, the polymer-chain
structure and electronic structure of the doped polymer are radically different from
those of the intact polymer. As typical cases, we will describe two kinds of lattice
structures of doped polythiophene (dopant content, 25 mole'%, per thiophene ring):
a polaron lattice and a bipolaron lattice. They are the regular infinite arrays of
polarons and bipolarons. The schematic polymer-chain structures are shown in
Figure 4-1 6. Band-structure calculations have been performed for polaron and/or
bipolaron lattices of poly( p-phenylene) [ 1241, polypyrrole [ 1241, polyaniline [ 1251,
polythiophene [ 124, 1261, and poly( p-phenylenevinylene) 11271, with the valenceeffective
Hamiltonian pseudopotential method on the basis of geometries obtained
by MO methods. The schematic electronic band structures shown in Figure 4-17