Diketopyrrolopyrrole-based acceptor-acceptor conjugated polymers: The importance of comonomer on their charge transportation nature

Besides the donor–acceptor (D–A) type, acceptor–acceptor (A–A) polymers are another class of important alternative conjugated copolymers, but have been less studied in the past. In this study, two kinds of A–A polymers, P1 and P2, have been designed and synthesized based on diketopyrrolopyrrole in combination with the second electron-deficient unit, perylenediimide or thieno[3,4-c]pyrrole-4,6-dione. UV–vis absorption spectroscopy revealed that these two kinds of polymers have a band gap of 1.28–1.33 eV. Their highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels are around −5.6 and −4.0 eV for P1 polymers, whereas −5.4 and −3.7 eV for P2 polymers, respectively. Density functional theory study disclosed that P1 backbone is in a vastly twisting state, whereas that of P2 is completely planar. Furthermore, organic field-effect transistor devices were fabricated using these two kinds of polymers as the active material. Of interest, the devices based on P1 polymers displayed n-channel behaviors with an electron mobility in the order of 10−4 cm2 V−1 s−1. In contrast, the P2-based devices exhibited only p-channel charge transportation characteristics with a hole mobility in the order of 10−3 cm2 V−1 s−1. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 2356–2366