Tuning Backbone Planarity in Thiadiazolobenzotriazole–Bis(thienothiophenyl)ethylene Copolymers for Organic Field-Effect Transistors

[1,2,5]Thiadiazolo[3,4-f]benzotriazole (TBZ) and bis(thieno[3,2-b]thiophenyl)ethylene (DTTE)-based conjugated polymers were designed and synthesized by Stille polycondensation, and the effect of the side chain alkyl positions on the optical, electrochemical, and charge-transporting properties in organic field-effect transistors was comprehensively studied. By optimizing the alkyl positions, we obtained semicrystalline polymers, but their hole mobilities were ∼0.1 cm2 V–1 s–1 due to the face-on dominant orientation. It was also found that the thiophene spacers, which have traditionally been present in the TBZ-based copolymers, are the source of the backbone torsion. Removal of the thiophene units produced an almost planar copolymer backbone with an edge-on and bimodal texture, which exhibited the improved hole mobility exceeding 0.4 cm2 V–1 s–1.