Head-to-Head Linked Dialkylbifuran-Based Polymer Semiconductors for High-Performance Organic Thin-Film Transistors with Tunable Charge Carrier Polarity

A planar backbone conformation is essential for enabling polymer semiconductors with high charge carrier mobility in organic thin-film transistors. Benefiting from the smaller van der Waals radius of the O atom in furan (versus the S atom in thiophene), alkylated furan exerts a reduced steric hindrance on neighboring arene, and it was found that the head-to-head (HH)-linked 3,3'-dialkyl-2,2'-bifuran (BFR) can attain a high degree of backbone planarity. Hence, BFR should be a promising building block for constructing polymer semiconductors with a planar backbone conformation and hold distinctive advantages over a dialkylbithiophene-based analogue, which is typically highly twisted. The alkyl chains on the 3 and 3' positions offer good solubility to the resulting polymers, which in combination with its planar backbone yields an improved molecular design window for developing high-performance polymer semiconductors, particularly those with a simple molecular structure and based on the acceptor co-unit without any solubilizing chains. When incorporated into polymer semiconductors, remarkably high hole and electron mobilities of 1.50 and 0.31 cm(2) V-1 s(-1) are obtained for BFR-based polymers FBFR-BO and CNBFR-C18 containing fluorinated and cyano-functionalized benzothiadiazole as the acceptor co-unit, respectively. Such mobilities are the highest values for HH-linked polymers and also among the best for furan-containing polymers. The results demonstrate that HH-linked dialkylbifuran is a highly promising building block for constructing organic and polymeric semiconductors, and this new approach by incorporating HH BFR offers several distinctive advantages for developing high-performance polymer semiconductors, including effective optoelectronic property tuning using a minimal number of aromatic rings, reduced structural complexity, facile material synthesis, good material solubility, and enriching the material library. In addition, the study offers important guidelines for future development of furan-based polymers and head-to-head linkage containing organic semiconductors.