Reversible and Efficient Photo-Switching of Azobenzene Derivatives on an Insulator Surface Investigated by nc-AFM

Studying single molecular switches is of interest for a better understanding of fundamental physical and chemical processes, but also in view of their possible use in smart materials and molecular nanotechnology.
Azobenzene is a prototypical molecular switch, which changes between trans and cis isomers at the central N=N bond upon an external stimulus. Adsorption on solid substrates allows the study on the single molecule scale using scanning probe microscopy, but it has been shown that metallic substrates strongly influence the switching properties[1,2].
Here, we report non-contact atomic force microscopy (nc-AFM) results on the switching of individual Azobenzene derived molecules on an insulating calcite surface. It is demonstrated that unlike on metals [3] the molecules retain their efficient photoisomerization properties known from solution. Furthermore, the photoisomerization is shown to be reversible and selective, depending on the exciting wavelength.

[1] Choi et al., Phys. Rev. Lett. 96, 156106 (2006); [2] Dri et al., Nature Nanotechnology 3, 649 (2008); [3] Comstock et al., Phys. Rev. Lett 99, 038301 (2007)