Donor–Acceptor Conjugated Polymers with Dithienocarbazoles as Donor Units: Effect of Structure on Semiconducting Properties

A series of donor–acceptor (D–A) conjugated polymers (CPs) comprising dithieno[2,3- b;7,6- b ]carbazole ( C1 ) or dithieno[3,2- b;6,7- b ]carbazole ( C2 ) as D unit and thienopyrroledione ( TPD ), isoindigo ( IID ), or diketopyrrolopyrrole ( DPP ) as A unit were synthesized, and their semiconducting properties were investigated with organic field-effect transistors (OFETs). Because of different bonding geometry of C1 and C2, the CPs based on these isomeric D units have distinct backbone conformation. The CPs based on C1 unit and all three A units show strong backbone curvature. In consequence, these polymers all formed amorphous films and exhibited low OFET mobility in the level of 10 –3 cm 2 /(V s). P(TPD-C2) and P(DPP-C2), which comprise C2 and TPD or DPP, both display pseudo-straight-shaped backbones and formed ordered films with the polymer backbones adopting edge-on orientation respective to the substrates. Accordingly, P(TPD-C2) and P(DPP-C2) exhibited the highest mobility of 0.31 and 1.36 cm 2 /(V s), respectively. However, P(IID-C2) could only form amorphous films probably owing to its highly stiff backbone, leading to a moderate OFET mobility (2.96 × 10 –2 cm 2 /(V s)). This implies that large fused aromatics are promising building blocks for high-mobility D–A CPs when polymer backbone conformation and rigidity are appropriately manipulated.