Organic materials have recently gained considerable attention for electronic applications, improving performance and sustainability to current technologies. Commercialized metal-based systems are generally expensive, toxic and difficult to recycle, however organic materials offer promising solutions. Viologens, N,N' di-quaternized bipyridyl salts, are a well-studied species exhibiting three reversible redox states, possessing valuable electrochromic and electron-accepting properties. These properties can be fine-tuned through synthesis by altering the nitrogen substituents and various counteranions. Currently, viologens have become of great interest as functional materials in a wide array of applications; a few to name include electrochromic devices, molecular machines, and organic batteries. This review highlights representative recent work and advances towards utilizing viologens in practical applications that currently compete with metal-based technologies. Additionally, modified viologens that can be further fine-tuned will be discussed.

Viologens, with their three stable redox states, present an intriguing alternative for functional materials. Aside from their strong electrochromism, they exhibit competitive reduction features that are relevant for several technologies. The application of viologens in electrochromic devices, molecular machines and organic energy‐storage systems is highlighted, as well as how modifying the scaffold impacts the parent system's properties. For more information see the Review article by T. Baumgartner and L. Striepe on page 16924 ff.

A straightforward synthetic route toward redox-active tri- and tetrastar phosphaviologen oligomers that show the intriguing ability of storing up to 8 electrons is reported.

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