Achieving chiral resolution in self-assembled supramolecular structures through kinetic pathways

Abstract

Chiral phase transitions were studied in a self-assembled 2,6-dibromoanthraquinones supramolecular system prepared on Au(111) using scanning tunneling microscopy. As the molecules were deposited at about 150 K, they formed heterochiral chevron structures (a racemate) consisting of two alternating prochiral molecular rows. When the as-deposited sample was warmed to 300 K followed by cooling to 80 K, phase-separated homochiral structures (a conglomerate), as well as the chevron structures, were observed. We propose molecular models for the structures that are in good agreement with ab initio studies and can be explained by hydrogen bonds and halogen bonds. We found that heterochiral chevron structures were more stable than homochiral structures due to two additional O center dot center dot center dot Br halogen bonds per molecule. We considered kinetic pathways for the phase transitions that were made possible via a disordered liquid phase entropically stabilized at 300 K. We show how chiral resolution can be achieved by exploiting kinetic paths allowed in supramolecular systems.