Gear systems are essential elementary mechanical units allowing the transmission of information over long distances and the conversion of the motive power of a motor through synchronized disrotatory motion of the cogwheels. They can also translate the changes in gear rotational speed into changes in rotational force. Researchers at CEMES-CNRS in partnership with research teams at University Paul Sabatier and Nara Institute of Science and Technology (NAIST), Japan, report in a new study published in Chemical Science a strategy to visualize snapshots of an ultrasmall gear train—an interconnected chain of molecular-scale gears—at work.
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. The most straightforward way to monitor the motion of molecular gears adsorbed on a surface is through static scanning tunneling microscopy images.
For these purposes, one of the teeth of the cogwheel subunits has been labelled through chemical modification. The teeth are made from porphyrins, a fragment already used in Nature for many processes like oxygen transportation (hemoglobin) or photosynthesis (chlorophyl). The electronic properties of one single tooth were modulated by varying the porphyrinic substituents or the nature of the central metal (nickel or zinc). Such tailored properties are important because one can observe the labelled teeth as differences in submolecular contrast by using scanning tunneling microscopy, thus facilitating imaging of cogwheels and monitoring of their rotation.
Cogwheel molecule as elementary unit of intermolecular gears on surface. The top arm (in red)has a different chemical structure to follow the rotation.
The pentaporphyrinic cogwheel prototypes are very complex molecules made up of at least 824 atoms (chemical formula C391H395BN28Ni5S3Ru) linked together in a very controlled manner. With their unique design and complexified chemical structure, these cogwheels will be used to build trains of gears on a metallic surface. In this arrangement, it will be possible to rotate a series of cogwheels in a coordinated way as in a conventional macroscopic gear train with a means to visualize such rotations.
Publication : Desymmetrised pentaporphyrinic gears mounted on metallo-organic anchors, S. Abid, Y. Gisbert, M. Kojima, N. Saffon-Merceron, J. Cuny, C. Kammerer, G. Rapenne, Chemical Science 2021.
DOI : 10.1039/d0sc06379g as Hot Article and with the Front Cover.
https://pubs.rsc.org/en/Content/ArticleLanding/2021/SC/D0SC06379G#!divAbstract
Contact : Gwénaël Rapenne, gwenael.rapenne [chez] cemes.fr & Claire Kammerer, claire.kammerer [chez] cemes.fr