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A molecular Swiss army knife

By combining an atom and a molecule on a surface with the help of a microscope using the tunnel effect, it is possible to construct a nano-object whose electronic and mechanical properties can be modulated according to the relative positions of the atom and the molecule. The diversity of properties obtained demonstrates the promising potential of this "trapping chemistry".
Published on 12 February 2018
Researchers deposited an isolated porphyrin molecule consisting of carbon rings (phenyl and pyrrole) and a larger central ring carrying two hydrogen atoms on a gold surface. Using the tip of a scanning tunneling microscope (STM), the porphyrin could be moved across the surface and brought into contact with a weakly bound gold atom.
The presence of a gold atom under a phenyl or pyrrole ring then induces a transfer of charges between the atom and the molecule, which can be finely adjusted according to the position of the atom relative to the molecule. This makes it possible to precisely control the electronic properties of the assembly.

If the gold atom is now placed at the center of the porphyrin and a hydrogen atom is removed, the molecule becomes capable of rotating under the effect of a tunnel current applied between the tip and the surface, through the nano-object. The result is a molecular rotor whose axis of rotation is set by the gold atom. This unique structure was entirely identified using atomistic modeling.

One final manipulation completely dehydrogenates the molecule, leading to a new nanostructure that is capable of moving across the gold surface when subjected to the STM tip's electric field.

This work was conducted by researchers from the Iramis, the CNRS and the Université Paris-Diderot.

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