Ternary Complex Formation by Cucurbit[7]uril Leads to Large Shifts in the Reduction Potentials of Suitable Viologens

Abstract

AbstractThis work addresses the effects of supramolecular complexation by cucurbit[7]uril (CB[7]) on the cell potential of aqueous batteries based on ferrocene and 4,4′‐bipyridinum (viologen) electroactive materials. It was previously known that the oxidation potential of cationic ferrocene derivatives is shifted to more positive values by the formation of highly stable 1 : 1 binary complexes with CB[7]. Here, we found that the formation of 1 : 2 ternary complexes between suitably designed viologens and CB[7] leads to a pronounced shift to more negative values in the first one‐electron reduction potential of the viologen. Combining these two effects, we predict that the corresponding aqueous redox flow battery (RFB) ‐containing cationic ferrocene in the catholyte and viologen in the anolyte‐ will exhibit a potential of 1.04 V in the absence of CB[7] and 1.30 V in the presence of suitable concentrations of CB[7]. This substantial potential increase might be improved in future research, as the supramolecular complexation effect seems to be rather general.