Photoisomerization for a molecular switch in contact with a surface

The photoisomerization properties of an azobenzene derivative on a thin insulating NaCl layer on Ag(111) are investigated with a low-temperature scanning tunneling microscope and density functional calculations. Illumination with UV light at 365 nm induces the reversible direct isomerization of the adsorbed species, while visible light does not lead to any changes. This unexpected behavior cannot be explained by the change of the electronic structure upon adsorption on the inert surface. It is rationalized in terms of electrostatic interactions caused by the atomistic details of the surface.