Enantiodiscrimination at Electrochemical Interphases through Implementation of Inherently Chiral Selectors: New Insights and Perspectives

To achieve enantioselective electrochemistry and electroanalysis, electron transfer processes at the electrochemical interphase require the presence of a suitable enantiopure chiral selector, resulting in energetically different diastereoisomeric conditions for the two probe enantiomers.1 A groundbreaking strategy was recently proposed, based on the use of molecular selectors endowed with "inherently chirality", i.e. with chirality and key functional properties originating from the same structural element, which in our case identifies with the main molecular backbone, featuring a tailored torsion with a racemization energy barrier too high to be overcome at room temperature. In such conditions, large peak potential differences have been observed in voltammetry for the enantiomers of even very different chiral probes either (i) working in achiral media, on electrode surfaces modified with thin films of inherently chiral electroactive oligomers1,2 or (ii) working on achiral electrodes, implementing inherent chirality in the medium, particularly in ionic liquids ILs, either chiral themselves, or modified by a chiral additive,1,3 exploiting the peculiar IL high order at the interphase with a charged electrode. Both strategies are being now extended and refined, particularly aiming to collect clues for the elucidation of the recognition mechanism, as well as to highlight attractive applications. In the film case, advanced techniques are finely highlighting morphology, chemical composition as well as functional properties of inherently chiral electroactive oligomer films, both as electrode surfaces and as self standing membranes. In the media case, chiral and inherently chiral molecules are being studied both as bulk media and/or as media additives, with impressive results. A wide palette of selectors (films or media) and/or probes are being investigated, encompassing four classes of stereogenic elements, i.e. corresponding to stereocentre-based chirality, axial chirality, helical chirality and planar chirality. Finally, the outstanding enantiodiscrimination ability of the new selectors is being considered beyond molecular chiral probes, i.e. towards polarized light components (in terms of circular dichroism and circularly polarized luminescence) and electron spins (in magnetoelectrochemistry experiments). Not only impressive effects have been already observed, but fascinating correlations and connections are emerging among the three areas, worthy to be explored in detail, possibly providing further interpretative clues, as well as for possible exploitation in photonics and spintronics.