This dissertation presents a single molecule scanning tunneling microscopy and spectroscopy study of photomechanically switching molecules on a surface. The work is motivated by the following basic questions: (1) how do photoswitching molecules self-assemble and configure themselves when adsorbed to a surface and (2) how does the surface environment affect molecular photoswitching properties? These questions are relevant to the basic scientific challenge of successfully transferring molecules from solution to a condensed matter environment while leaving essential molecular mechanical properties intact. These results will have wide applicability in the field of molecular electronics and molecular nanomachines. The main finding of this work is that while in general surface-molecule interactions conspire to deactivate molecular photoswitching capability, molecular photoswitching on a surface can be enabled with proper engineering of the molecule-surface configuration. Future attempts at incorporating photoswitching molecules into devices will need to carefully consider this.

One particular class of photoswitching molecules were experimentally investigated and are presented in this dissertation. We present results of experimental investigations of azobenzene molecules (both bare and functionalized) adsorbed in multiple configurations (both in isolation and in group assemblies) on the Au(111) surface.