Enantioselective self-sorting on planar, π-acidic surfaces of chiral anion-π transporters

Self-sorting at interfaces is one of the big challenges we face to prepare the functional organic materials of the future. As a first and decisive step to self-sorting into pi-stacks or bundles, we here elaborate self-sorting of pi-dimers in solution. Design, synthesis and study of planar naphthalenediimides (NDIs) with one shielded and one free chiral pi-surface to direct self-assembly into dimers are described. Stereoisomers are isolated by chiral, preparative HPLC and characterized by X-ray crystallography. NMR studies show that racemates with almost planar, nearly identical pi-surfaces prefer uniform self-sorting into homodimers at large differences in pi-acidity and alternate self-sorting into heterodimers at small differences in pi-acidity. In contrast, enantiomers self-sort "narcissistically'' into heterodimers and diastereomers show moderate preference for homodimers. Whereas the lessons learned from dimerization are directly applicable to self-sorting of pi-stacks on surfaces, anion transport in lipid bilayers is shown to require a more subtle, somewhat inverse interpretation, with diastereomeric transporters differing dramatically in activity but the least visible supramolecule being confirmed as the best performer.