Atomic Force Microscopy Reveals Bistable Configurations of Dibenzo[a,h]thianthrene and their Interconversion Pathway

Abstract

We investigated dibenzo[a,h]thianthrene molecules adsorbed on ultrathin layers of NaCl using a
combined low-temperature scanning tunneling and atomic force microscope. Two stable configurations
exist corresponding to different isomers of free nonplanar molecules. By means of excitations from
inelastic electron tunneling we can switch between both configurations. Atomic force microscopy with
submolecular resolution allows unambiguous determination of the molecular geometry, and the pathway
of the interconversion of the isomers. Our investigations also shed new light on contrast mechanisms in
scanning tunneling microscopy.