Influence of fluorination in π-extended backbone polydiketopyrrolopyrroles on charge carrier mobility and depth-dependent molecular alignment

A series of pi-extended polydiketopyrrolo[3,4-c]pyrroles with a varying degree of fluorination on the thiophene-phenyl-thiophene comonomer was synthesized by Stille polycondensation. The influence of the degree of fluorination was studied with regard to the polymer properties, such as absorption, electrochemical redox potentials, the solid state structure as well as depth-dependent molecular alignment in thin films. Additionally, their performance in organic field effect transistors was evaluated. Whereas fluorination slightly increases the alkyl lamella and shrinks the pi-pi spacings, the coherence lengths were found to improve significantly in both directions. All polymers were found to be p-type materials when employed in organic field effect transistors (OFET). These devices can be tuned towards ambipolarity in the case of the tetrafluorinated copolymer upon thermal annealing.