Dipolar Nanocars Based on a Porphyrin Backbone

Multiply engaged molecular gears composed of a cerium(IV) double-decker of a triptycene-functionalized porphyrin

Intramolecular gearing motions are studied in a cerium(IV) double-decker of triptycene-functionalised porphyrins using single crystal X-ray analysis and variable temperature 1H-NMR.

Directing and Understanding the Translation of a Single Molecule Dipole

Understanding the directed motion of a single molecule on surfaces is not only important in the well-established field of heterogeneous catalysis but also for the design of artificial nanoarchitectures and molecular machines. Here, we report how the tip of a scanning tunneling microscope (STM) can be used to control the translation direction of a single polar molecule. Through the interaction of the molecular dipole with the electric field of the STM junction, it was found that both translations and rotations of the molecule occur. By considering the location of the tip with respect to the axis of the dipole moment, we can deduce the order in which rotation and translation take place. While the molecule-tip interaction dominates, computational results suggest that the translation is influenced by the surface direction along which the motion takes place.

Design and Manipulation of a Minimalistic Hydrocarbon Nanocar on Au(111)

Nanocars are carbon-based single-molecules with a precise design that facilitates their atomic-scale control on a surface. The rational design of these molecules is important in atomic and molecular-scale manipulation to advance the development of molecular machines, as well as for a better understanding of self-assembly, diffusion and desorption processes. Here, we introduce the molecular design and construction of a collection of minimalistic nanocars. They feature an anthracene chassis and four benzene derivatives as wheels. After sublimation and adsorption on an Au(111) surface, we show controlled and fast manipulation of the nanocars along the surface using the tip of a scanning tunneling microscope (STM). The mechanism behind the successful displacement is the induced dipole created over the nanocar by the STM tip. We utilized carbon monoxide functionalized tips both to avoid decomposition and accidentally picking the nanocars up during the manipulation. This strategy allowed thousands of maneuvers to successfully win the Nanocar Race II championship.

Extended Tripodal Hydrotris(indazol-1-yl)borate Ligands as Ruthenium-Supported Cogwheels for On-Surface Gearing Motions

This paper reports the synthesis of ruthenium-based molecular gear prototypes composed of a brominated or non-brominated pentaphenylcyclopentadienyl ligand as an anchoring unit and a tripodal ligand with aryl-functionalized indazoles as a rotating cogwheel. Single crystal structures of the ruthenium complexes revealed that the appended aryl groups increase the apparent diameter of the cogwheel rendering them larger than the diameter of the anchoring units and consequently making them suitable for intermolecular gearing motions once the complexes will be adsorbed on a surface.

Divergent Synthesis of Molecular Winch Prototypes

We report the synthesis of conceptually new prototypes of molecular winches with the ultimate aim to investigate the work performed by a single ruthenium-based molecular motor anchored on a surface by probing its ability to pull a load upon electrically-driven directional rotation. According to a technomimetic design, the motor was embedded in a winch structure, with a long flexible polyethylene glycol chain terminated by an azide hook to connect a variety of molecular loads. The structure of the motor was first derivatized by means of two sequential cross-coupling reactions involving a penta(4-halogenophenyl)cyclopentadienyl hydrotris(indazolyl)borate ruthenium(II) precursor and the resulting benzylamine derivative was next exploited as key intermediate in the divergent synthesis of a family of nanowinch prototypes. A one-pot method involving sequential peptide coupling and Cu-catalyzed azide-alkyne cycloaddition was developed to yield four loaded nanowinches, with load fragments encompassing triptycene, fullerene and porphyrin moieties.

Desymmetrised pentaporphyrinic gears mounted on metallo-organic anchors

Mastering intermolecular gearing is crucial for the emergence of complex functional nanoscale machineries. However, achieving correlated motion within trains of molecular gears remains highly challenging, due to the multiple degrees of freedom of each cogwheel. In this context, we designed and synthesised a series of star-shaped organometallic molecular gears incorporating a hydrotris(indazolyl)borate anchor to prevent diffusion on the surface, a central ruthenium atom as a fixed rotation axis, and an azimuthal pentaporphyrinic cyclopentadienyl cogwheel specifically labelled to monitor its motion by non-time-resolved Scanning Tunneling Microscopy (STM). Desymmetrisation of the cogwheels was first achieved sterically, i.e. by introducing one tooth longer than the other four. For optimal mechanical interactions, chemical labelling was also investigated as a preferential way to induce local contrast in STM images, and the electronic properties of one single paddle were modulated by varying the porphyrinic scaffold or the nature of the central metal. To reach such a structural diversity, our modular synthetic approach relied on sequential cross-coupling reactions on a penta(p-halogenophenyl)cyclopentadienyl ruthenium(ii) key building block, bearing a single pre-activated p-iodophenyl group. Chemoselective Sonogashira or more challenging Suzuki-Miyaura reactions allowed the controlled introduction of the tagged porphyrinic tooth, and the subsequent four-fold cross-couplings yielded the prototypes of pentaporphyrinic molecular gears for on-surface studies, incorporating desymmetrised cogwheels over 5 nm in diameter.

Nanocars with Permanent Dipoles: Preparing for the Second International Nanocar Race

With the desire to synthesize surface-rolling molecular machines that can be translated and rotated with extreme precision and speed, we have synthesized a series of five nanocars. Each structure features a permanent dipole moment, generated by an N,N-dimethylamino- moiety on one end of the car coupled with a nitro group on the other end. These cars are designed to be stimulated with an electric field gradient from a scanning probe microscopy tip. The nanocars all possess unexplored combinations of structural features: tert-butyl wheels, short alkyne chassis, and combination sets of wheels including one set of tert-butyl wheels and another set of larger adamantane wheels on the same car. Each of these features needs to be assessed as preparation for the second International Nanocar Race that is taking place in 2022.