ABSTRACT
ABSTRACT: The flexibility of conjugated polymer chains is investigated theoretically for polythiophene and polypyrrole. The possibility for individual rings to rotate around interring single bonds is evaluated by means of quantum chemical calculations, using the ab initio RHF 3-21G and the semiempirical AMI methods. The rotation barriers in thiophene and pyrrole oligomers are of the order of a few kcal/mole, thereby allowing significant flexibility in solution or in the melt. The introduction of charges on the chain, corresponding to the doping process, leads to a dramatic stiffening of the conjugated backbone, as indicated by a 20-fold increase in the rotation barrier.
