Chiral Conflict among Different Helicenes Suppresses Formation of One Enantiomorph in 2D Crystallization

Diastereomeric
inter­actions in 2D crystals formed at solid
surfaces serve as excellent models for understanding molecular recognition
in biomineralization. Adsorption of a penta­helicene racemate
on a Au(111) surface leads to 2D conglomerate crystallization, i.e.,
homo­chiral mirror domains, as observed by scanning tunneling
microscopy. Upon mixing 26% of (M)-hepta­helicene
into the racemate monolayer, only the (M)-penta­helicene
enantio­morph is observed. This effect is explained by a preferred
hetero­chiral inter­action between the different helicene
species, suppressing the formation of the pure (P)-penta­helicene enantio­morph. These results shine new
light onto stereo­selective molecular recognition mediated by
van der Waals forces.