Viologens and Their Application as Functional Materials

Abstract

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.

Dynamic supramolecular polymers built from cucurbit[n]urils and viologens

“…1,1‐Di(hydrocarbyl)‐4,4′‐bipyridinium salts, best known as viologens (V 2+ ), exhibit unique redox and chemical behaviors which have proved highly valuable to the construction of functional molecular materials, including for applications in organic electronics, organic batteries and for the development of molecular machines. Viologen derivatives are for instance commonly used as electron‐poor components in donor–acceptor type host–guest complexes, as seen in the work of Stoddart's group on ‘blue‐box’‐based rotaxanes and catenanes .…”

Redox‐Triggered Folding of Self‐Assembled Coordination Polymers incorporating Viologen Units

“…Indeed, intramolecular π‐dimers can be readily produced when both viologens involved in the dimer are mechanically connected through suitable spacers, such as a propyl chain, whose size and flexibility is perfectly suited to promote an efficient orbital overlap between both radicals. The viologen group thus constitutes a building block of great interest and its redox‐induced dimerization can be exploited to trigger motions at the molecular level and to provide access to fascinating responsive supramolecular molecules and materials …”

Narrow‐Bandgap Chalcogenoviologens for Electrochromism and Visible‐Light‐Driven Hydrogen Evolution

“…[9] In recent years,s everal groups have made efforts to combine heteroatoms and viologens.F or example,rigid phosphaviologens (P-RV), [10] doubly phosphorus-bridged viologen (DPMV) [11] or disulfide viologen [12] were developed by doping Po rSi nto viologen scaffolds,w hich showed enhanced electrochemical and electrochromic properties. [13] By incorporation of silole/germole or thiazole with viologen, the solid-state phosphorescent dipyridinometal-loles [14] and fluorescent bipyridinium thiazolothiazole derivatives [15] have been reported. Evidently,combination of main group elements and viologen is an efficient strategy to develop viologen derivatives with broad promising applications.…”