Coplanar Donor–Acceptor Semiconducting Copolymers to Achieve Better Conjugated Structures: Side‐Chain Engineering. Issue 16 (23rd May 2017) - Pei, Mingyuan
Abstract : The connecting point of branched alkyl chains on the donor–acceptor semiconducting copolymers significantly affects the intra‐ and intermolecular conformations of the copolymers. The longer spacer between the backbone and side substituents enhances the coplanarity and conjugation of the copolymer with a narrower π‐overlap spacing, resulting in higher electrical properties. Abstract : It is reported on the allocation effects of branched alkyl chains, when used as solubility and ordering enhancers of the conjugated donor–accepter ( D – A ) copolymer backbones, on the ordering and π–π overlapping of the copolymers, that drastically affect the electrical properties of organic field‐effect transistors (OFETs). Triisopropylsilylethynyl‐benzo[1, 2‐ b :4, 5‐ b ′]dithiophene (TIPSBDT) and diketopyrrolopyrrole (DPP)‐based copolymers, which have two linear alkyl spacers (methylene ( C 1) or butylene ( C 4)) between the DPP and side‐substituent (C10 H21 )CH(C8 H17 ), are synthesized by Suzuki cross‐coupling. These copolymer films are spun cast onto a polymer‐treated SiO2 dielectric surface, and some are further thermally annealed. The longer spacer, C 4, is found to efficiently enhance the coplanarity and conjugation of the D – A backbone, while the C 1 does not. The resulting C 4‐bridged TIPSBDT‐DPP‐based copolymer readily develops a superior π‐extended layer on the dielectric surface; the edge‐on chains with randomly oriented side chains can be closely packed with a short π‐planar distance ( d (010) ) of 3.57 Å. Its properties are superior to those of the short spacer C 1 system with d (010) ≈3.93 Å. The C 4‐bridged TIPSBDT‐DPP copolymer films yield a field‐effect mobility up to 1.2 cm 2 V −1 s −1 in OFETs, 12 times as higher than that of the C 1 spacer system.