Motions of single molecules inserted in a self-assembled monolayer matrix of a bicyclo[2.2.2]octane derivative on Au(111)

The motion of single conjugated molecules inserted in a self-assembled monolayer (SAM) matrix composed of a spherical bicyclo[2.2.2]octane derivative was observed using scanning tunnelling microscopy at room temperature. Two kinds of conjugated molecules, i.e. benzenemethanethiol and 4-biphenylmethanethiol, were inserted in the SAM matrix. It was revealed that the isolated single molecules exhibited two types of motions. One was the change in tilt of the molecular axis at a fixed position, and the other was lateral motion in the SAM matrix. These motions of the single molecules due to thermal energy at room temperature were most likely caused by large and mobile vacancies of single molecular defects in the SAM matrix.