Thieno[3,2-b]pyrrole and Benzo[c][1,2,5]thiadiazole Donor–Acceptor Semiconductors for Organic Field-Effect Transistors

Two p-type donor-acceptor (D-A) semiconducting small molecules were synthesized to investigate the effect of the backbone curvature on the organic field-effect transistor performance. The backbone curvature of the donor-acceptor small molecules was modified by changing the spacer group from bithiophene to thienothiophene. Bithiophene to thienothiophene spacer groups were placed between 4 H -thieno[3,2- b ]pyrrole (donor) and benzo[ c ][1,2,5]thiadiazole (acceptor) to generate TP-BT4T-TP and TP-BT2TT-TP donor-acceptor molecules. A good charge carrier mobility of 2.59 × 10 -2 cm 2 V -1 s -1 was measured for the curved molecule ( TP-BT4T-TP ), while the linear molecule analog ( TP-BT2TT-TP ) only gave a low mobility of 5.41 × 10 -5 cm 2 V -1 s -1 after annealing at 120 °C in bottom-contact bottom-gate devices. Out-of-plane grazing-incidence X-ray diffraction analysis revealed more drastic thermally induced crystallinity for TP-BT4T-TP as compared to TP-BT2TT-TP , explaining the difference observed in the performance of devices fabricated from each molecule.