Biaxially Extended Conjugated Polymers with Thieno[3,2-b]thiophene Building Block for High Performance Field-Effect Transistor Applications

Biaxially thiophene side chain extended thieno[3,2-b]thiophene (TT2T)-based polymers, PTTT2T, P2TTT2T, PTTTT2T, and PTVTTT2T, were synthesized by Stile coupling polymerization with different conjugated moieties of thiophene (T), bithiophene (2T), thieno[3,2-b]thiophene (TT), and thiophene-vinylene-thiophene (TVT), respectively. The electronic properties of the prepared polymers could be effectively tuned because the variant pi-conjugated building block affected the backbone conformation and the resulted morphology. The morphology of the thin films characterized by atomic force microscopy and grazing incidence X-ray diffraction showed that that P2TTT2T and PTVTTT2T thin films possessed a better molecular packing with a nanofiber structure owing to their coplanar backbone. The average field-effect mobilities of PTTT2T, P2TTT2T, PTTTT2T, and PTVTTT2T were 6.7 x 10(-6), 0.36, 2.2 x 10(-3), and 0.64 cm(2) V-1 s(-1) (maximum 0.71), respectively, attributed to the coplanarity of polymer skeleton. In addition, the fabricated PET devices showed a high on/off ratio over 10(7) under ambient for over 3 months, suggesting the excellent environmental stability. The above results demonstrated that the biaxially extended fused thiophene based conjugated polymers could serve as a potential candidate for organic electronic device applications.