Dimension-Controlled π-Electronic Ion-Pairing Assemblies

Ion-pairing assemblies consisting of appropriately designed π-electronic ionic species afford various functional supramolecular assemblies including crystals and soft materials based on the anisotropic orientation of π-electronic ionic species through electrostatic and other weak noncovalent interactions. Organized assemblies comprising π-electronic ionic species as dimension-controlled assemblies provide unique and tunable mesophases and electronic properties. As components of dimension-controlled ion-pairing assemblies, π-electronic ion pairs are important and have been prepared through (i) synthesis of π-electronic units bearing ionic substituents, (ii) synthesis of genuine π-electronic ions, and (iii) complexation of π-electronic receptors and ions. In (ii) and (iii), appropriate ion-exchange processes are necessary. Based on these strategies, fascinating ion pairs and their assemblies have been constructed, resulting in an elucidation of the assembling behaviors of π-electronic ion pairs. In this article, ion-pairing assemblies consisting of precisely designed π-electronic ionic species are described, with a focus on the preparation methods, structures, and properties.