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

[Image: see text] 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 4H-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.