Diketopyrrolopyrrole-Based π-Conjugated Copolymer Containing β-Unsubstituted Quintetthiophene Unit: A Promising Material Exhibiting High Hole-Mobility for Organic Thin-Film Transistors

A new diketopyrrolopyrrole-based pi-conjugated copolymer (PDPP5T) with high molecular weight has been synthesized by Stille coupling polymerization of 3,6-bis(5-bromothiophen-2-yl)-2,5-bis(2-octyldodecyl)pyrrolo-[3,4-c]-pyrrole-1,4(2H,5H)-dione with alpha,alpha'-bis(trimethylstannyl)-terthiophene. Its hole mobility without thermal annealing reaches 1.08 cm(2) V-1 s(-1), and a higher hole mobility of 3.46 cm(2) V-1 s(-1) is obtained annealed at 200 degrees C directly in an air atmosphere. This indicates that introducing a longer beta-unsubstituted quinquethiophene (5T) unit into the main-chain of DPP-oligothiophene copolymer produces much pronounced p-type behavior and also reduces the steric hindrance of the bulk side-chain groups, which is favorable to enhance the molecular ordering capability at low temperatures and improve the organic thin-film transistors (OTFT) performances. This work demonstrates that PDPP5T is a promising material that can be applied to the cost-effective and large-scale production of OTFTs.