Photo-Induced Polymerization and Isomerization on the Surface Observed by Scanning Tunneling Microscopy

In this paper, an azobenzene derivative containing two diacetylene groups is synthesized and its self-assembly at a surface investigated using scanning tunneling microscopy (STM). Both the azo-benzene and diacetylene groups are photoactive, and the results show that surface assemblies of the targeted compound undergo polymerization following irradiation at 254 nm and reversible isomerization following alternating irradiation at 365 nm and with visible light. This is the first report of a STM investigation observing both photopolymerization and photoisomerization simultaneously for the same molecular assembly at an interface. The target molecule allows one to induce sequential and reversible structural changes to surface assemblies via multiple optical treatments, and is thus of both fundamental interest for surface science and engineering. These results provide experimental and theoretical guidance for the fabrication of future molecular optoelectronic devices.