Unveiling the Inverse-Handed Self-Discrimination of Helicenes with Twisted π-Surfaces by Liquid Chromatography

Helicenes, with their rigid, helically twisted π-conjugated backbones, have garnered growing attention as potential chiral selectors, yet their capabilities for enantioselective molecular recognition remain largely unexplored. In this study, the enantioselective recognition behavior of [6]helicene-immobilized silica-monolithic capillaries is systematically investigated when employed as chiral stationary phases in liquid chromatography. Under normal-phase conditions, these helicene-based stationary phases effectively separated the enantiomers of 1,1'-binaphthyl analogues and helicene analogues, primarily via π interactions. In contrast, reversed-phase conditions suppressed these weaker chiral π-driven interactions, resulting in markedly lower enantioselectivities. Notably, all [6]helicene-immobilized columns exhibited a pronounced preference for "inverse-winding" helicene analytes, suggesting a self-discrimination mechanism in which helicenes bind more strongly to their opposite-handed counterparts. Overall, these findings provide a blueprint for the design of novel helicene-based materials and chiral stationary phases that leverage finely tuned π interactions.