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

Biaxially thiophene side chain extended thieno­[3,2-<i>b</i>]­thiophene (TT2T)-based polymers, PTTT2T, P2TTT2T, PTTTT2T, and PTVTTT2T, were synthesized by Stille coupling polymerization with different conjugated moieties of thiophene (T), bithiophene (2T), thieno­[3,2-<i>b</i>]­thiophene (TT), and thiophene–vinylene–thiophene (TVT), respectively. The electronic properties of the prepared polymers could be effectively tuned because the variant π-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 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 × 10^–6, 0.36, 2.2 × 10^–3, and 0.64 cm² V^–1 s^–1 (maximum 0.71), respectively, attributed to the coplanarity of polymer skeleton. In addition, the fabricated FET devices showed a high on/off ratio over 10⁷ 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

Isoindigo-Based Semiconducting Polymers Using Carbosilane Side Chains for High Performance Stretchable Field-Effect Transistors

Isoindigo-based conjugated polymers, PII2T-C6 and PII2T-C8, with carbosilane side chains have been designed and synthesized for stretchable electronic applications. The carbosilane side chains offerred a simple synthetic pathway to evaluate long and branched side chains in high yields and were prepared with a six or eight linear spacer plus two hexyl or octyl chains after branching. The studied polymers showed a high charge carrier mobility of 8.06 cm² V^–1 s^–1 with an on/off current ratio of 10⁶ as probed using a top-contact transistor device with organized solid state molecular packing structures, as investigated through grazing-incidance X-ray diffreaction (GIXD) and atomic force microscopy (AFM) technique systematically. The studied polymers, more attractive, exhibited superior thin film ductility with a low tensile modulus in a range of 0.27–0.43 GPa owing to the branched carbosilane side chain, and their mobility was remained higher than 1 cm² V^–1 s^–1 even under a 60% strain along parallel or perpendicular direction to the tensile strain. Such polymer films, in addition, can be simultaneously operated over 400 stretching/releasing cycles and maintained stable electrical properties, suggesting the newly designed materials possessed great potential for next-generation skin-inspired wearable electronic application with high charge carrier mobility, low tensile modulus, and stable device characteristics during stretching