Inducing the Rotation of a Single Phenyl Ring with Tunneling Electrons

Abstract

We report on the electron induced intramolecular rotation of a single phenyl ring of an azobenzene derivative adsorbed on a Au(111) surface using a low-temperature scanning tunneling microscope (STM). By proper functionalization of each of the two azobenzene's phenyl rings with CN end groups, we are able to identify two distinct isomers at the metal surface corresponding to two possible alignments of the functional groups in the trans conformer. Tunneling electrons induce molecular motion and intramolecular conformational changes both on isolated molecules and H-bonded molecular islands. Particular enhancement is observed for the electrons resonantly tunneling through affinity levels, which is consistent with electronic molecular excitations as the basic mechanism for this manipulation process. On the basis of quantum chemical calculations of a free azobenzene molecule, we propose a dynamical model for the ring-rotation pathways, which includes the electric field in the STM junction to effectively couple electronic excitation with intramolecular rotations.

Current-induced conformational switching in single-molecule junctions

“…Thus, the molecule returns to its original conformation with high probability, and conformational switching occurs rarely. Such low-quantum-yield switching has been observed in recent experiments [16,27,28]. For instance, STM measurements on azobenzene derivatives show that only one out of 10 10 tunneling electrons induces a switching event [16].…”

“…An essential requirement for electric circuits of nanoscale dimensions is a molecular device that can be switched between two distinct conductive states. Because of intrinsic bistabilities, many single-molecule junctions reveal switching behavior, e.g., involving cis and trans isomers of a molecule [15][16][17][18][19][20][21][22][23][24][25].…”

Actuated Transitory Metal−Ligand Bond As Tunable Electromechanical Switch

“…This is indicative of an instability of the imaged structure triggered by tunneling electrons. 3,12 To understand this behavior, the tunneling current was measured in open feedback loop conditions as a function of time. Current traces recorded in the fuzzy area show an oscillation between two values (see Figure 2a), which we label as low-and high-conductance state.…”

Structural changes in a Schiff base molecular assembly initiated by scanning tunneling microscopy tip

“…Surface-bounded molecular switches, rotors and motors are fascinating since they can be exposed to external stimuli [4][5][6] and investigated by surface analysis methods [7][8][9][10]. Recent studies have shown that surface-bounded molecular switches and rotors can be used in experimental techniques such as scanning tunneling microscopy and spectroscopy (STM/STS) which also allow the measurement of molecular switching/rotor rates and energy barriers [11][12][13][14].…”