Cyclodextrin-threaded conjugated polyrotaxanes as insulated molecular wires with reduced interstrand interactions

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Abstract
Control of intermolecular interactions1 is crucial to the exploitation of molecular semiconductors for both organic electronics2 and the viable manipulation and incorporation of single molecules3 into nano-engineered devices. Here we explore the properties of a class of materials that are engineered at a supramolecular level4,5,6,7,8,9,10 by threading a conjugated macromolecule, such as poly(para-phenylene), poly(4,4′-diphenylene vinylene) or polyfluorene through α- or β-cyclodextrin rings, so as to reduce intermolecular interactions and solid-state packing effects that red-shift and partially quench the luminescence11. Our approach preserves the fundamental semiconducting properties of the conjugated wires, and is effective at both increasing the photoluminescence efficiency and blue-shifting the emission of the conjugated cores, in the solid state, while still allowing charge-transport. We used the polymers to prepare single-layer light-emitting diodes with Ca and Al cathodes, and observed blue and green emission. The reduced tendency for polymer chains to aggregate allows solution-processing of individual polyrotaxane wires onto substrates, as revealed by scanning force microscopy.