Molecular motor crossing the frontier of classical to quantum tunneling motion

Abstract

<jats:p>The reliability by which molecular motor proteins convert undirected energy input into directed motion or transport has inspired the design of innumerable artificial molecular motors. We have realized and investigated an artificial molecular motor applying scanning tunneling microscopy (STM), which consists of a single acetylene (C<jats:sub>2</jats:sub>H<jats:sub>2</jats:sub>) rotor anchored to a chiral atomic cluster provided by a PdGa(111) surface that acts as a stator. By breaking spatial inversion symmetry, the stator defines the unique sense of rotation. While thermally activated motion is nondirected, inelastic electron tunneling triggers rotations, where the degree of directionality depends on the magnitude of the STM bias voltage. Below 17 K and 30-mV bias voltage, a constant rotation frequency is observed which bears the fundamental characteristics of quantum tunneling. The concomitantly high directionality, exceeding 97%, implicates the combination of quantum and nonequilibrium processes in this regime, being the hallmark of macroscopic quantum tunneling. The acetylene on PdGa(111) motor therefore pushes molecular machines to their extreme limits, not just in terms of size, but also regarding structural precision, degree of directionality, and cross-over from classical motion to quantum tunneling. This ultrasmall motor thus opens the possibility to investigate<jats:italic>in operando</jats:italic>effects and origins of energy dissipation during tunneling events, and, ultimately, energy harvesting at the atomic scales.</jats:p>

One-way rotation of a chemically anchored single molecule-rotor

“…In scanning tunneling microscopy (STM) experiments, the rotation of a single molecule triggered by inelastic tunneling effects has been the focus of research for a long time. [3][4][5][6][7][8][9][10][11] The production of minute mechanical work was recently demonstrated, 12 opening new routes for the rational design of unidirectional molecule-rotors. 8,9 However, only a few examples of controlled directional rotation of organic molecules around a vertical axis have been demonstrated yet, 6,[8][9][10] and further experimental and theoretical work is needed to understand the relation between inelastic electronic excitation and motion of a single molecule.…”

STM induced manipulation of azulene-based molecules and nanostructures: the role of the dipole moment

“…The target di-tert-butyl-2-isocyanoazulene-1,3-dicarboxyl (BCA) (5) was obtained in four steps starting from commercially available tropolone in an overall yield of 58.2% and is stable under ambient conditions. Tosylated tropolone (1) was obtained from tropolone in a near quantitative reaction following a literature protocol.…”

“…The movement of single molecules on a surface induced by tunneling electrons is presently in the focus of research, especially concerning the excitation mechanisms, 1 the possibility of performing work, 2 and the construction of molecular rotors and motors. [3][4][5] Furthermore, the miniaturization of mechanical components to the atomic limit opens new fundamental scientific questions connected to the way electric energy is converted into movement in molecules. [3][4][5] Scanning tunneling microscopy (STM) at low temperature is a unique tool to investigate single molecules on surfaces and is applied for triggering on-surface chemical reactions, 6 analysing electronic properties, 7 manipulating atoms and molecules, 8 and driving nanocars.…”

“…[3][4][5] Furthermore, the miniaturization of mechanical components to the atomic limit opens new fundamental scientific questions connected to the way electric energy is converted into movement in molecules. [3][4][5] Scanning tunneling microscopy (STM) at low temperature is a unique tool to investigate single molecules on surfaces and is applied for triggering on-surface chemical reactions, 6 analysing electronic properties, 7 manipulating atoms and molecules, 8 and driving nanocars. 1,[9][10][11][12] The influence of electric fields in STM manipulation has been well discussed for several decades.…”

Non-Adiabatic Dynamics Simulations of a Light-Driven Molecular Motor in Solution

“…New generations pursue an increase in the rotational frequency of the motor up to the MHz scale. [9][10][11][12][13][14] In this quest to achieve higher frequencies, a precise spatio-temporal control is best if the working rotary process is well understood and its collective behavior in solution or on attached surfaces 15,16 can be predicted at molecular level.…”