Isomerization of azobenzene derivatives near cobalt islands on Au(111)

• This is the first study that investigates the isomerization behaviour of azobenzene-based molecular switches in locally different environments, namely adsorption on a Au(111) surface and on thin cobalt islands, at the single molecule level. By analyzing the isomerization rates for molecules with different surroundings, we observe that isomerization can be induced successfully on both, gold and cobalt areas, with similar rates. Moreover, no local field enhancement, caused by plasmonic excitations within Co nanostructures, can be observed, probably due to the small thickness of the cobalt islands. We studied the influence of cobalt nanostructures on the photo-isomerization of meta -TBA molecules on a Au(111) surface by scanning tunneling microscopy. Switching from trans to cis isomers of individual molecules was investigated by scanning tunneling microscopy (STM) for different molecule locations with respect to cobalt islands on the surface. Specifically, we studied the isomerization rates for molecules on top of cobalt (Co) islands, on clean Au(111) areas and on Au(111) areas that are close to Co islands. We observe that isomerization can be induced successfully on both, gold and cobalt areas, with similar rates. Comparing different gold areas, about the same number of switching events per molecule are found on cobalt-free Au(111) terraces and in Au(111) areas if a Co island is located nearby. This finding shows that no local field enhancement, caused by plasmonic excitations within Co nanostructures, is present, at least not in strength that would substantially affect the molecular photoisomerization process.