Polycyclic aromatic hydrocarbons- like molecules as precursors for triazafullerenes formation by cyclodehydrogenation

Polycyclic Aromatic hydrocarbons are very interesting because of their potential use as precursors for a controlled synthesis of fullerenes, alternative to those based on the graphite vaporization. This type of molecules could lose hydrogen upon temperature, rendering possible the formation of closed fullerenes of the type C60. Moreover, ab initio calculations [1] predict that aromatic hydrocarbons could loss the hydrogen when are annealed at ?800K. In this work, we focus our interest on the adsorption and the interaction of C57H33N3 [2] on Au(111) surface, from coverages ranging from 0.1 ML to 5 ML, and the possibility of forming closed fullerenes from this molecular layer. For room temperature deposition, we found that the molecules diffuse on the surface rendering difficult the observation with STM. NEXAFS measurements show, for coverages of 1 ML, that the molecules are adsorbed lying parallel to the surface, while for coverages of 5 ML the molecules exhibit a random distribution. After sample annealing at temperatures near 800K, for coverage smaller than 1 ML the molecule reacts with the surface being anchored to it. This nucleation process starts from the step edges, and for coverages close to 1ML, it forms a complete molecular layer. In this situation the binding energy of both N1s and C1s core-level XPS peaks indicates a charge transfer process to the substrate. This core level analysis shows that the carbon atoms near the nitrogen are responsible for this charge transfer process. Finally, for annealing at temperatures higher than 800K, STM shows the occasional formation of triazafullerenes C57H2N3 with similar structure to a deposited C60 molecule. [1] C. Koper, Tesis Doctoral, Non-Alternant Polycyclic Aromatic Hydrocarbons versus Closed Carbon Surfaces, Verbonden aan het Debye Instituut de Universiteit Utrecht, The Netherlands (2003). [2] B. Gómez-Lor, A. M. Echavarren, Organic Letters, 6 (2004) 2993.