Trópos and Átropos Biindole Chiral Electroactive Monomers: A Voltammetry and HPLC Comparative Insight

A series of 2,2'-biindole-based inherently chiral electroactive monomers are comparatively investigated with their 3,3' analogues as an excellent study case of two equivalent redox centres interacting through a torsional barrier. The twin peak potential splitting observed in voltammetry for the first oxidation of the biheteroaromatic core accounts for the energy barrier height: the lower the barrier, the larger the peak potential splitting, with modulation by solvent and temperature. The height of the energy barrier is determining for the electrochemical and spectroscopic features of the monomers as well as for their configurational stability and applicability for enantioselection purposes. The 3,3' monomers, featuring large twin peak splittings in CV, are "tropos" systems with a low torsional barrier, so they cannot exist as stable enantiomers at room temperature. Instead their 2,2' isomers, with much smaller twin peak splittings, are "atropos" systems and can be separated by enantioselective HPLC into stable enantiomers, providing powerful "inherently chiral" selectors with outstanding enantioselection properties in chiral electroanalysis and electrochemistry as well as in chiroptical spectroscopy, with fascinating reciprocal correlations.