From Saddle-Shaped to Planar Cyclic Oligothienoacenes: Stepped-Cyclization and Their Applications in OFETs

A series of cyclic oligothienoacenes (1, 3, and 4) have been successfully synthesized through a stepped-cyclization synthetic strategy from tetra[3,4-thienylene] (2). Single-crystal X-ray diffraction analysis combined with theoretical calculations elucidated that the molecular configuration transforms from the saddle shape of 2 to the quasi-saddle shape (3b, 3c), then to the quasi-helical shape (4b), and at last to the quasi-plane shape (1, 3a, 4a). Organic field-effect transistors (OFETs) based on 1, 3a, and 4a were fabricated. The field-effect mobilities of 7.5 × 10^-4, 2.6 × 10^-3, and 6.8 × 10^-4 cm² V^-1 s^-1 were obtained for 1, 3a, and 4a, respectively. Compounds 3a and 4a can act as air-stable p-type organic semiconductors, while 1 is sensitive to the air.