Odd-Even Effects in Chiral Phase Transition at the Liquid/Solid Interface

Chiral selection on inorganic crystalline surfaces represents one of the most promising avenues to the separation of enantiomers. However, there are competing influences at play: on the one hand, the confinement to the surface seems to enhance chiral discrimination between enantiomers; on the other hand, racemic patterns tend to possess higher packing density therewith higher stability. A clear picture on the delicate balance between these two opposing factors is missing. We address this issue in monolayers of alkylated dehydrobenzo[12]annulene (DBA) derivatives at the liquid/solid interface by a detailed investigation of the relationship between packing density and 2D chirality. We report on chiral phase transitions, evolving from homochiral low density porous networks to enantiomeric excess, racemic, or homochiral densely packed structures, by using scanning tunneling microscopy (STM) as a visualization tool. The changes in monolayer chirality in response to increased packing density, however, are strongly correlated with molecular structural features such as the length of the alkyl chains and in particular their parity. While heterochiral lattices are indeed denser than its enantiomorphous counterparts, close packing does not necessarily favor racemic crystallization: the azimuthal orientation of building blocks in a domain may play a decisive role. In light of the popularity of using alkyl chains to adhere molecules onto a surface, we believe that our findings may have implications for predictive chiral recognition and resolution processes.

Publication year:2017

BOF-keylabel:yes

IOF-keylabel:yes

BOF-publication weight:2

CSS-citation score:1

Authors:International

Authors from:Higher Education

Accessibility:Open