Backbone Curvature in Polythiophenes

A series of five polymers containing different benzodithiophene isomers copolymerized with alkylated dithiophene have been synthesized and characterized in terms of their semiconducting properties. Because of the different bonding geometry of the benzodithiophene monomers, a varying degree of curvature is introduced into the polymer backbone chain. The influence of this curvature on the solubility, the electronic levels, the morphology in a film, and the charge carrier mobility in organic field-effect transistors has been investigated. It turns out that an increased degree of curvature improves the solubility, but decreases the order in the film. As a result, the polymer with an intermediate degree of curvature yields the highest charge-carrier mobilities. These findings shall serve as guideline for the rational design of other semiconducting polymers.