title: Polarity engineering of conjugated polymers by variation of chemical linkages connecting conjugated backbones.
abstract: The fine tuning of the dominant polarity in polymer semiconductors is a key issue for high-performance organic complementary circuits. In this paper, we demonstrate a new methodology for addressing this issue in terms of molecular design. In an alternating conjugated donor-acceptor copolymer system, we systematically engineered the chemical linkages that connect the aromatic units in donor moieties. Three donor moieties, thiophene-vinylene-thiophene (TVT), thiophene-acetylene-thiophene (TAT), and thiophene-cyanovinylene-thiophene (TCNT), were combined with an acceptor moiety, thienoisoindigo (TIID), and finally, three novel TIID-based copolymers were synthesized: PTIID-TVT, PTIID-TAT, and PTIID-TCNT. We found that the vinylene, acetylene, and cyanovinylene linkages decisively affect the energy structure, molecular orbital delocalization, microstructure, and, most importantly, the dominant polarity of the polymers. The vinylene-linked PTIID-TVT field-effect transistors (FETs) exhibited intrinsic hole and electron mobilities of 0.12 and 1.5 × 10(-3) cm(2) V(-1 )s(-1), respectively. By contrast, the acetylene-linked PTIID-TAT FETs exhibited significantly improved intrinsic hole and electron mobilities of 0.38 and 0.03 cm(2) V(-1) s(-1), respectively. Interestingly, cyanovinylene-linked PTIID-TCNT FETs exhibited reverse polarity, with hole and electron mobilities of 0.07 and 0.19 cm(2) V(-1) s(-1). As a result, the polarity balance, which is quantified as the electron/hole mobility ratio, was dramatically tuned from 0.01 to 2.7. Our finding demonstrates a new methodology for the molecular design of high-performance organic complementary circuits.
authors.affiliation: †School of Materials Science and Engineering and Research Institute for Green Energy Convergence Technology (REGET), Gyeongsang National University, Jinju 660-701, Korea.
authors.forename: Hui-Jun
authors.initials: HJ
authors.lastname: Yun
authors.affiliation: ‡Department of Chemical Engineering and Center for Advanced Soft Electronics, Pohang University of Science and Technology (POSTECH), Pohang 790-784, Korea.
authors.forename: Hyun Ho
authors.initials: HH
authors.lastname: Choi
authors.affiliation: †School of Materials Science and Engineering and Research Institute for Green Energy Convergence Technology (REGET), Gyeongsang National University, Jinju 660-701, Korea.
authors.forename: Soon-Ki
authors.initials: SK
authors.lastname: Kwon
authors.affiliation: §Department of Chemistry, Gyeongsang National University and Research Institute of Nature Science (RINS), Jinju 660-701, Korea.
authors.forename: Yun-Hi
authors.initials: YH
authors.lastname: Kim
authors.affiliation: ‡Department of Chemical Engineering and Center for Advanced Soft Electronics, Pohang University of Science and Technology (POSTECH), Pohang 790-784, Korea.
authors.forename: Kilwon
authors.initials: K
authors.lastname: Cho
keywords: ambipolarity; chemical linkage; organic transistor; polarity; thienoisoindigo