Tunable charge-transport polarity in thienothiophene-bisoxoindolinylidene-benzodifurandione copolymers for high-performance field-effect transistors

N-Type semiconducting polymers are important materials for modern electronics but limited in variety and performance. To design a new n-type polymer semiconductor requires a judicious trade-off between structural parameters involving both backbone and side-chain modifications. The appeal of backbone modification emerges from the tunable electronic structures and conformational control. To control these effects typically needs installation of substituents such as halogens. In a polymer system with high molecular complexity, a few common substituents such as methyl and methoxy groups are an underdeveloped area of chemical space. In this work, we study the substituent effects in methyl- and methoxy-substituted thienothiophene-bis(oxoindolinylidene)benzodifurandione copolymers on field-effect performances. The two substituents affect the conformations of the backbone and increase the frontier orbital energy levels of the polymers. Using such electronic effects, we are able to tune the charge transport behaviors from n-channel to ambipolar. This strategy allows further substitution patterns for backbone modification in other polymer semiconductors.