Polarity Engineering of Conjugated Polymers by Variation of Chemical Linkages Connecting Conjugated Backbones

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 donoracceptor copolymer system, we systematically engineered the chemical linkages that connect the aromatic units in donor moieties. Three donor moieties, thiophenevinylenethiophene (TVT), thiopheneacetylenethiophene (TAT), and thiophenecyanovinylenethiophene (TCNT), were combined with an acceptor moiety, thienoisoindigo (TIID), and finally, three novel TIID-based copolymers were synthesized: PTIIDTVT, PTIIDTAT, and PTIIDTCNT. 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 PTIIDTVT field-effect transistors (FETs) exhibited intrinsic hole and electron mobilities of 0.12 and 1.5 x 10(-3) cm(2) V-1 s(-1), respectively. By contrast, the acetylene-linked PTIIDTAT 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 PTIIDTCNT 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.