Train of Single Molecule-Gears

Abstract

Two molecule-gears, 1.2 nm in diameter with six teeth, are mounted each on a single copper adatom separated exactly by 1.9 nm on a lead surface using a low-temperature scanning tunneling microscope (LT-STM). A functioning train of two molecule-gears is constructed complete with a molecule-handle. Not mounted on a Cu adatom axle, this ancillary molecule-gear is mechanically engaged with the first molecule-gear of the train to stabilize its step-by-step rotation. Centered on its Cu adatom axle, the rotation of the first gear of the train step by step rotates the second similar to a train of macroscopic gears. From the handle to the first and to this second molecule-gear, the exact positioning of the two Cu adatom axles on the lead surface ensures that the molecular teeth-to-teeth mechanics is fully reversible.

Transmitting Stepwise Rotation among Three Molecule-Gear on the Au(111) Surface

“…Transmitting a rotation along a train of gears is an essential prerequisite for the construction of molecular mechanical machines. To the best of our knowledge, there was no transmission of rotations realized between more than two molecule-gears 17 . Here, we present a collective transmission of rotation between three molecule-gears 2 (Figure 7).…”

“…Another breakthrough came several years later, in 2007, when a molecular rack-and-pinion device was demonstrated by using a low-temperature STM, known as the first interlocked molecular gear device 16 , while the first complete rotation of a molecule-gear induced by STM manipulation was demonstrated in 2009 5 . Recently, on a Pb(111) surface, the transmission of motion between two hexa-tert-butyl-pyrimidopentaphenylbenzene (HB-NBP) molecules mounted each on a single Cu adatom was demonstrated, using a third HB-NBP molecule as a "molecular handle" 17 .…”

“…Many degrees of freedom of the follower are activated while pushing on the driver as observed in ref. 17 . In other words, the collective rotational degrees of freedom of the follower, activated by the STM tip, are in competition with many other possible intramolecular mechanical modes.…”

Mechanics of Molecule-Gears with Six Long Teeth

“…20 For (3), the central core was up to now a small circular shape molecular group such as a cyclopentadiene or a phenyl core. 10,11,15 Larger in diameter, a central molecular chemical core like hexabenzocoronene 21 generally leads to a non-stable rotation around an atomic axle. This is because such a nanographene like molecular core does not offer a lateral diffusion barrier height in the centre of this core that would be large enough to ensure a stable rotation around a single centred ad-atom.…”

“…No chemical tag was inserted at this stage because of its inefficiency on the Pb(111) surface. 15 For (5): the ground state PES, it is still out of the scope of the new field of molecule-gear mechanics optimization because of the large lateral size of the supporting surface required for the calculations of the large number of mechanical degrees of freedom involved per molecule-gear. One can expect to calculate a minimum energy path for rotation transmission along a long train of gears but not the complete ground state PES as a function of a few characteristic angles per molecule-gear.…”