Tailored formation of N-doped nanoarchitectures

To unveil the effect of different surfaces on the PAHs, we selected two hetero-aromatic molecules, namely C57H33N3, a ‘crushed triaza-fullerene’, and C40H24N2, a precursor of N-doped nanographene. By combining various surface-science techniques, such as Scanning Tunneling Microscopy, Density Functional Theory and synchrotron based spectroscopic techniques, we are able to describe at an atomistic point of view the structural and electronic transformation of both.

Upon thermal activation on a highly reactive surface such as Pt(111), precursor 1 and precursor 4 transform into respectively a triaza-fullerene 2 and N-doped nanographene 5 by cyclodehydrogenation (i.e. the cleavage of the C-H bonds and the subsequent formation of new C-C bonds in aromatic rings). This is because the as-deposited molecule interacts strongly with the surface and cannot diffuse, so it can only undergo an intramolecular structural transformation. The image shows the structural transformation of the molecules as observed by the STM upon annealing on a highly reactive surface (follow the arrow ‘a’).

When the molecules are deposited on a coinage metal such as Au(111), the weak interaction between the surface and the adsorbate permits diffusion. Upon annealing, the (cyclo)dehydrogenated molecules meet and bind together to form polymeric covalent chains 3 and 6, whose building blocks are (partially) cyclodehydrogenated precursors. STM images and conjectural structures of these chains can be found in the image by following the arrow ‘b’.



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