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

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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 cm 2 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.