Side-chain modulation of dithienofluorene-based copolymers to achieve high field-effect mobilities† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c6sc04129a Click here for additional data file.

Chia-Hao Lee, Yu-Ying Lai, Jhih-Yang Hsu, Po-Kai Huang and Yen-Ju Cheng* A ladder-type dithieno[3,2-b:6,7-b0]fluorene (DTF), where the central fluorene is fused with two outer thiophene rings at its 2,3and 6,7-junctions, is developed. The pentacyclic DTF monomers were polymerized with dithienodiketopyrrolopyrrole (DPP) acceptors to afford three alternating donor– acceptor copolymers PDTFDPP16, PDTFDPP20, and PDTFDPP32 incorporating different aliphatic side chains (R1 group at DTF; R2 group at the DPP moieties). The side-chain variations in the polymers play a significant role in determining not only the intrinsic molecular properties but also the intermolecular packing. As evidenced by the 2-dimensional GIXS measurements, PDTFDPP16 with octyl (R1) and 2ethylhexyl (R2) side chains tends to align in an edge-on p-stacking orientation, whereas PDTFDPP20 using 2-butyloctyl (R1) and 2-ethylhexyl (R2) adopts a predominately face-on orientation. PDTFDPP32 with the bulkiest 2-butyloctyl (R1) and 2-octyldodecyl (R2) side chains shows a less ordered amorphous character. The OFET device using PDTFDPP20 with a face-on orientation determined by GIXS measurements achieved a high hole-mobility of up to 5 cm V 1 s . The high rigidity and coplanarity of the DTF motifs play an important role in facilitating intramolecular 1-dimensional charge transport within the polymer backbones. The implementation of main-chain coplanarity and side-chain engineering strategies in this research provides in-depth insights into structure–property relationships for guiding development of high-mobility OFET polymers.