Multi-Stage Amphoteric Redox Hydrocarbons Based on a Phenalenyl Radical

Molecular design and properties of amphoteric redox hydrocarbons are reviewed. Our molecular design is based on a phenalenyl radical, which has a non-bonding molecular orbital with an occupation number of one and is known to behave as a two-stage amphoteric redox system. We have prepared eight amphoteric redox compounds containing two or three phenalenyl units. Cyclic voltammetry showing small E1sum values confirms the high amphotericity of these compounds. The properties of ionic redox species generated are also investigated. At the last part of this account, we show some aspects of a singlet biradicaloid character that originates from a small HOMO–LUMO gap.