Viologens are an important class of redox-active compounds, often used as electron acceptors in fundamental photochemical and electrochemical studies, as well as redox components in rotaxane-based molecular electronics and electrochromic devices. However, viologens are often practically limited in redox-based applications by the instability of their reduced forms to Oxygen. Here, we discuss the design, self-assembly, electrochemical behaviors, and Oxygen stability of viologen species incorporated in a hierarchical supramolecular assembly in water. Two different bis-viologen dimers are presented, each reduced in the presence of the macrocyclic host cucurbit[8]uril (CB[8]). This results in the sequential folding and then encapsulation of the reduced viologen dimers. Interestingly, the normally degenerate 2 e<sup>-</sup>redox wave (4+/2+ transition) of the bis-viologen species separates into two separate 1 e<sup>-</sup>redox waves in the presence of CB[8]. This new 3+ mono-radical complex displays unique UV/Vis absorbance and a significant stabilization to molecular Oxygen. The supramolecular chemistry leading to the formation and stability of these reduced viologen dimers will be discussed.

Supramolecular assembly of unusually stable viologen radical species in water

ACS Spring 2022

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