Helicenes at surfaces: topological self-assembly and electron spin filtering

3. 10. 2022  11:00  

CEITEC BUT, Purkyňova 123, Brno; S building, large meeting room 

Prof. Karl-Heinz Ernst 

University of Zurich, Department of Chemistry

Surfaces functionalized with helically shaped aromatic hydrocarbons, so-called helicenes, are of interest for chiroptical electronic devices or for electron-spin filtering. While self-assembled layers facilitate studying interesting phenomena, covalently linked chiral modified materials would be much more robust and therefore better suited for applications. For that matter, on-surface chemistry has become an important approach towards new functional interfaces that are hardly available by solution chemistry. We briefly report stereoselective chemistry of different helicene species on noble metal surfaces. The stereochemical analysis of diastereoisomers formed on the surface is performed by scanning tunneling microscopy (STM) and non-contact atomic force microscopy (ncAFM). Depending on the site of bromination at the helical backbone, the Ullmann coupling reaction of different bromohelicenes proceeds stereospecifically to heterochiral or homochiral products. The diastereoselective chemistry is explained by topochemical effects due to the on-surface alignment of the helicenes during reaction.