Surface manipulation of a curved polycyclic aromatic hydrocarbon-based nano-vehicle molecule equipped with triptycene wheels.

With a central curved chassis, a four-wheeled molecule-vehicle was deposited on a Au(111) surface and imaged at low temperature using a scanning tunneling microscope. The curved conformation of the chassis and the consequent moderate interactions of the four wheels with the surface were observed. The dI/dV constant current maps of the tunneling electronic resonances close to the Au(111) Fermi level were recorded to identify the potential energy entry port on the molecular skeleton to trigger and control the driving of the molecule. A lateral pushing mode of molecular manipulation and the consequent recording of the manipulation signals confirm how the wheels can step-by-step rotate while passing over the Au(111) surface native herringbone reconstructions. Switching a phenyl holding a wheel to the chassis was not observed for triggering a lateral molecular motion inelastically and without any mechanic push by the tip apex. This points out the necessity to encode the sequence of the required wheels action on the profile of the potential energy surface of the excited states to be able to drive a molecule-vehicle.

Simultaneous and coordinated rotational switching of all molecular rotors in a network.

A range of artificial molecular systems has been created that can exhibit controlled linear and rotational motion. In the further development of such systems, a key step is the addition of communication between molecules in a network. Here, we show that a two-dimensional array of dipolar molecular rotors can undergo simultaneous rotational switching when applying an electric field from the tip of a scanning tunnelling microscope. Several hundred rotors made from porphyrin-based double-decker complexes can be simultaneously rotated when in a hexagonal rotor network on a Cu(111) surface by applying biases above 1 V at 80 K. The phenomenon is observed only in a hexagonal rotor network due to the degeneracy of the ground-state dipole rotational energy barrier of the system. Defects are essential to increase electric torque on the rotor network and to stabilize the switched rotor domains. At low biases and low initial rotator angles, slight reorientations of individual rotors can occur, resulting in the rotator arms pointing in different directions. Analysis reveals that the rotator arm directions are not random, but are coordinated to minimize energy via crosstalk among the rotors through dipolar interactions.

Chiroptical properties of an optically pure dicopper(I) trefoil knot and its enantioselectivity in luminescence quenching reactions

Chiroptical spectroscopy is used to investigate the properties of an optically pure dinuclear copper(I) trefoil knot. For the metal-to-ligand charge tranfer (MLCT) transition in the visible region (520 nm), the electric and magnetic transition dipole moments are determined from absorption and circular dichroism spectra: 2.8 Debye and 0.5 Bohr magneton (muB). Circular polarization in the luminescence (CPL) of the knot is determined and this allows the electric and magnetic transition dipole moments in emission to be calculated: 0.02 Debye and 0.003 muB. The large difference between the moments in absorption and emission shows that the emission observed does not originate directly from the 1MLCT state. Given the low probability for radiative decay we assign the long-lived emitting excited state to a 3MLCT state. The copper(I) trefoil knot is found to quench the emission from TbIII and EuIII(dpa)3(3)-(dpa = pyridine-2,6-dicarboxylate) with a bimolecular rate constant of 3.2 and 3.3 x 10(7)M(-1)S(-1), respectively, at room temperature in water-acetonitrile (1:1 by volume). Experimental results indicate that the (lambda)-knot preferentially quenches the lambda enantiomer of the lanthanide complex with an enantioselectivity (ratio of quenching rate constants for lambda and lambda: kqlambda/kqdelta) of 1.012+/-0.002 for EuIII and 1.0180+/-0.003 for TbIII.

Controlled clockwise and anticlockwise rotational switching of a molecular motor.

The design of artificial molecular machines often takes inspiration from macroscopic machines. However, the parallels between the two systems are often only superficial, because most molecular machines are governed by quantum processes. Previously, rotary molecular motors powered by light and chemical energy have been developed. In electrically driven motors, tunnelling electrons from the tip of a scanning tunnelling microscope have been used to drive the rotation of a simple rotor in a single direction and to move a four-wheeled molecule across a surface. Here, we show that a stand-alone molecular motor adsorbed on a gold surface can be made to rotate in a clockwise or anticlockwise direction by selective inelastic electron tunnelling through different subunits of the motor. Our motor is composed of a tripodal stator for vertical positioning, a five-arm rotor for controlled rotations, and a ruthenium atomic ball bearing connecting the static and rotational parts. The directional rotation arises from sawtooth-like rotational potentials, which are solely determined by the internal molecular structure and are independent of the surface adsorption site.