para-Aminoazobenzenes-Bipolar Redox-Active Molecules

Azobenzenes (ABs) are versatile compounds featured in numerous applications for energy storage systems, such as solar thermal storages or phase change materials. Additionally, the reversible one-electron reduction of these diazenes to the nitrogen-based radical anion has been used in battery applications. Although the oxidation of ABs is normally irreversible, 4,4'-diamino substitution allows a reversible 2e^- oxidation, which is attributed to the formation of a stable bis-quinoidal structure. Herein, we present a system that shows a bipolar redox behaviour. In this way, ABs can serve not only as anolytes, but also as catholytes. The resulting redox potentials can be tailored by suitable amine- and ring-substitution. For the first time, the solid-state structure of the oxidized form could be characterized by X-ray diffraction.