Single-Molecule Observation of Redox Reactions Enabled by Rigid and Isolated Tripodal Molecules

Tracking various chemical reactions, including electrochemical
and photochemical reactions at the single-molecule level, is expected
to yield a great deal of knowledge from both fundamental and applied
aspects. In this study, we report on a methodology to track the electronic-state
changes of redox reactions at the single-molecule level by using electrochemical
scanning tunneling microscopy (EC-STM). EC-STM is powerful for single-molecule
analysis of redox reactions, but previous studies have shown difficulties
separating the structural and electronic contributions due to orientational
changes during the redox reaction. Here, we visualize the electronic-state
changes of a single ferrocene associated with redox reactions using
EC-STM by synthesizing and fabricating a monolayer of structurally
rigid tripodal molecules based on triptycene, which act as ideal anchors
to preserve a constant distance between the electrode and the ferrocene
moieties. This methodology paves the way for versatile single-molecule
measurements of important phenomena at the solid–liquid interface,
such as photochemistry and heterogeneous catalysis.