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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 (C1) or butylene (C4)) between the DPP and side-substituent (C10H21) CH(C8H17)-, 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, C4, is found to efficiently enhance the coplanarity and conjugation of the D-A backbone, while the C1 does not. The resulting C4-bridged TIPSBDTDPP-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 C1 system with d(010) ≈3.93 Å. The C4-bridged TIPSBDT-DPP copolymer films yield a field-effect mobility up to 1.2 cm² V-1 s-1 in OFETs, 12 times as higher than that of the C1 spacer system. [ABSTRACT FROM AUTHOR]

A donor-acceptor (D-A) semiconducting copolymer, PDPP-TVT-29, comprising a diketopyrrolopyrrole (DPP) derivative with long, linear, space-separated alkyl side-chains and thiophene vinylene thiophene (TVT) for organic field-effect transistors (OFETs) can form highly π-conjugated structures with an edge-on molecular orientation in an as-spun film. In particular, the layerlike conjugated film morphologies can be developed via short-term thermal annealing above 150°C for 10 min. The strong intermolecular interaction, originating from the fused DPP and D-A interaction, leads to the spontaneous self-assembly of polymer chains within close proximity (with π-overlap distance of 3.55 Å) and forms unexpectedly long-range π-conjugation, which is favorable for both intra- and intermolecular charge transport. Unlike intergranular nanorods in the as-spun film, well-conjugated layers in the 200°C-annealed film can yield more efficient charge-transport pathways. The granular morphology of the as-spun PDPP-TVT-29 film produces a field-effect mobility (μFET) of 1.39 cm2 V-1 s-1 in an OFET based on a polymer-treated SiO 2 dielectric, while the 27-Å-step layered morphology in the 200°C-annealed films shows high μFET values of up to 3.7 cm2 V-1 s-1 . [ABSTRACT FROM AUTHOR]