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| Accueil>La recherche>nanosciences>STM & AFM>molecular caltrops | ||||||||||||||
Toward persistent shape molecules :
Christophe Coudret, Sébastien Gauthier,
Jérôme Lagoute, Hao Tang, Tomaso Zambelli |
| Our objective is to design molecules
that would be thick enough to show parts mechanically uncoupled
to the surface. An "Urchin-like" structure with a centrosymmetrically
substituted core provides a way to keep some degrees of freedom
and simplify the image analysis since only one type of adsorption
should be observed: |
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"CALTROPS"
The first attempts involved the use of an heteroatom to shape the
molecule : a metal (chromium) for the octahedron, a column 14 element
(silicon) for the tetrahedron. |
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Images feature several types of objects:
one of these is a four-lobe structure, that can be interpreted as
a partly dissociated complex [1]. |
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As for chromium imaging show several objects, the
ternary symmetry of some of them may be attributed to a silicon
carbon bond breaking |
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SPIROBIFLUORENE To prevent the molecule's break-down, we thought of increasing
the number of bonds to rigidify the core, and to switch to a lighter
element, carbon. |
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The spirobifluorene [2] core is prepared in three
steps, and can be functionnalized easily to yield symmetrical compounds. |
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UHV-STM images at R.T. on Cu (1,0,0) show "bumps"
of a relatively high height (6Å). Calculations require a very
strong molecule distortion due to Van der Waals interaction with
the surface (69 kcal/mol between the two conformations). The optimized
structure is then consistent with the observed height. |
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Toward low-frequency vibrational spectroscopy
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1- Grillo S. et al. Chem. Phys. Lett. 2001, in the press. 2- Tour J. et al. J. Org. Chem. 1996, 61, 6906-6921.
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