Supramolecular Self-Assembly and Photo-Induced Transition of a Halogenated Azo-Benzene Molecule on Au(111) Surface

Azobenzene derivatives are a unique class of photo-switch molecules with promising potential for nanoscale optical applications. We have studied the self-assembly and photo-induced mechanical switching of azobenzene derivatives on Au(111) at the single-molecule level by using scanning tunneling microscope (STM). 4,4 '-Dibromo-azobenzene (Br-AB) molecules are assembled into two types of well-ordered structures on Au(111) surfaces in the trans-isomer configuration. Br-AB molecules experienced configurational changes from trans-to-cis photo-isomerization upon the exposure to the UV light. This photo-isomerization of Br-AB molecules was observed to occur at random sites of ordered structure, evidenced by the appearance of bright protrusions with the height increment. Our results may open up new routes to engineer nanoscale photo-switch molecular devices.