Modulation of Majority Charge Carrier from Hole to Electron by Incorporation of Cyano Groups in Diketopyrrolopyrrole-Based Polymers

A thienylene–vinylene–thienylene (TVT) derivative with cyano groups in the 3- and 3′-positions was synthesized as a building block of semiconducting polymers for high mobility organic field effect transistors (OFETs). (E)-1,2-Di-(3-cyano­thiophen-2-yl)­ethene (2CNTVT) was copolymerized with diketopyrrolopyrrole (DPP) units via Stille coupling reaction to give 2DPP-2CNTVT and 7DPP-2CNTVT. The properties of these two polymers were compared with those of the corresponding polymers without cyano groups in TVT (2DPP-TVT and 7DPP-TVT). The effects of CN groups and branched alkyl position were found to have a significant influence on the optical, electrochemical, morphological, and charge transporting properties of the polymers. The average hole mobilities of OFETs fabricated with 2DPP-TVT and 7DPP-TVT OFETs were 1.63 and 2.2 cm² V^–1 s^–1, respectively, and the average electron mobility for both 2DPP-2CNTVT and 7DPP-2CNTVT OFETs was 1.2 cm² V^–1 s^–1.