Chiral surfaces via self-assembly of helical aromatic molecules

Karl-Heinz Ernst

Molecular Surface TechnologiesSwiss Federal Laboratories for Materials Testing and Research (EMPA)

Dübendorf, Switzerland

Chirality, i.e. the phenomenon of objects existing in two conformations like non-superimposable mirror images, is ubiquitous in nature. In particular the self-organization ofchiral molecules into helical architectures is of fundamental importance in life. On theother hand, the interest in transfer of chirality from single molecules into mesoscopic chiralensembles is based on its application in liquid crystal (LC) technologies. However, themechanism of chirality induction, i.e. the process in which the molecular chirality ismapped onto a supramolecular ensemble is still poorly understood.A promising approach for getting insight into the process of intermolecular chiralitytransfer is the investigation of the self-assembly of chiral molecules on solid surfaces,where the chirality transfer is limited to two dimensions. In particular, this allows the use ofscanning tunneling microscopy (STM) which is an excellent tool for studying molecularpattern formation. By means of the self-assembly of helically shaped polyaromatichydrocarbons on single-crystal surfaces, as investigated via variable-temperature STM,aspects like i) surface enantiomorphism, ii) the transfer of chirality from single moleculesinto mesoscopic and macroscopic structures, iii) chiral amplification, and iv) 2D-spontaneous separation will be addressed. Finally, a new approach for the determination ofthe absolute conformation of chiral molecules will be presented.