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Abstract:
Direct arylation (DA) is emerging as a highly promising method to construct inexpensive conjugated materials for large-area electronics from simple and environmentally benign building blocks. Here, we show that exclusive α-C–H selectivity is feasible in the DA of π-extended monomers having unsubstituted thiophene or furan units, leading to fully linear materials. Two new naphthalene diimide-based conjugated copolymers—P(FuNDIFuF4) and P(ThNDIThF4), composed of naphthalene diimide (NDI), furan (Fu) or thiophene (Th), and tetrafluorobenzene (F4)—are synthesized. Insight into structure–function relationships is given by density functional theory (DFT) calculations and variety of experimental techniques, whereby the effect of the heteroatom on the optical, structural, and electronic properties is investigated. The use of furan (Fu) allows for enhanced solubilities, a smaller dihedral angle between NDI and Fu as a result of the smaller size of Fu, and a smaller π–π-stacking distance in the solid state. P(FuNDIFuF4) also exhibits a more edge-on orientation compared to P(ThNDIThF4). Despite these advantageous properties of P(FuNDIFuF4), P(ThNDIThF4) exhibits the highest electron mobility: ∼1.3 cm2/(V s), which is a factor of ∼3 greater than that of P(FuNDIFuF4). The enhanced OFET performance of P(ThNDIThF4) is explained by reduced orientational disorder and the formation of a terrace-like thin-film morphology.
