Two donor-acceptor copolymers, PI and P2, containing the novel donor component benzo[2,1-b:3,4-b':5,6-c '']trithiophene were synthesized. Both polymers show small pi-stacking distances (0.35 nm for P1 and 0.37 nm for P2) due to the use of the disklike-shaped donor unit. However, they exhibit remarkable differences in supramolecular organization, film microstructure, and transistor performance. Indeed, PI reveals a distinct supramolecular organization in the bulk in comparison to conventional conjugated polymers, including P2. Interestingly, no charge carrier transport was observed for PI in field-effect transistors, while P2 exhibited a hole mobility of up to 0.04 cm(2) V-1 s(-1). This variation in device behavior is attributed to the evidently different degree of curvature in the polymer backbone induced by the introduction of two additional thiophene units in P2.