Electrochemistry of, and in, chiral and inherently chiral ionic liquids

Ionic liquids ILs are attractive media for electrochemical processes, providing both solvent and supporting electrolyte and featuring an extremely well defined structure at the interphase with a charged electrode, resembling a semisolid crystal or a bulk liquid crystal, extending for many layers, also standing in the presence of water traces, and possibly tunable by in-situ present additives. Thus chiral ionic liquids CILs (many of which have been so far proposed, although still nearly unexplored by electrochemists) can transmit chiral information much more effectively than chiral organic solvents or supporting electrolytes.[1] Moreover, considering the recent performances of "inherently chiral" electrodes, the best results should come from "inherently chiral" ionic liquids ICILs [1]. Actually impressive enantiodiscrimination performances in terms of large potential differences for different chiral probes have been observed in enantiopure ICILs with inherently chiral dications based on atropoisomeric biheteroaromatic scaffolds, even using them (or other family terms solid at room T) as low-concentration chiral additives in common achiral ILs. [2,3] Similar performances have also been observed dissolving in an achiral IL an inherently chiral additive based on a different stereogenic element, a thiahelicene helical scaffold. An interesting comparative study has been recently performed, applying both voltammetry and impedance, with a family of chiral (but not "inherently chiral") biobased ionic liquids, as such and as chiral additives in achiral ionic liquids [4]. Several interpretative possibilities are being considered. The support of Fondazione Cariplo/Regione Lombardia "Avviso congiunto per l’incremento dell’attrattività del sistema di ricerca lombardo e della competitività dei ricercatori candidati su strumenti ERC - edizione 2016” (Project 2016-0923) is gratefully acknowledged. [1] Curr. Opin.Electrochem. 8 (2018) 60-72; [2] Angew. Chem. Int. Ed. 56 (2017) 20179-2082; [3] Electrochem. Comm. 89 (2018) 57-61; [4] Electrochim. Acta 298 (2019) 194-209.