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 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 x 10(-2) cm2 V-1 s(-1) was measured for the curved molecule (TP BT4T TP), while the linear BGBC Devices molecule analog (TP BT2TT TP) only gave a low mobility of 5.41 x 10(-5) cm(2) V-1 s(-1) after annealing at 120 degrees 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.