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.