Oligoaniline crystals: morphology control, hierarchical assembly and structure-property relationships

Short-chain oligomers of aniline are attractive semi-metallic materials for applications as organic electrodes or hole-transporting layers in organic photovoltaics. However, conventionally processed oligoanilines are often amorphous, which limits their conductivities and carrier transport mobilities. Here, we report a simple solvent-exchange method that can render a variety of oligoanilines and their derivatives into crystals of different shapes and dimensions, including 1-D fibers and wires, 2-D ribbons, and 3-D plates, hollow spheres, porous sheets, and flower-like structures. Dopant ions are also simultaneously incorporated into the crystals during self-assembly, allowing them to become conducting. Mechanistic studies suggest that the higher order crystals arise from the most primitive nanofibrillar morphology via hierarchical assembly, providing insights into a general approach to control organic crystal morphologies. Selected area electron diffraction studies reveal their single crystalline nature.