A tailored formation of N-doped fullerene, nanographene or 2D polyaromatic networks by on-surface dehydrogenation of heteroaromatics

Trabajo presentado en el 19th International Vacuum Congress (IVC-19), celebrado en París del 9 al 13 de septiembre de 2013.The controlled on-surface synthesis of intricate ¿-electron systems may ultimately overcome the limits of conventional synthesis, which often faces severe problems if large, fragile or insoluble molecules are to be prepared in solution and subsequently deposited on a solid substrate. Surface-assisted cyclodehydrogenation or dehydrogenative polymerisation of polycyclic heteroaromatic hydrocarbons (PAH) is one of the most important strategies for bottom-up assembly of new nanostructures from their constituent molecular building blocks1. Although diverse compounds have been formed in recent years using this methodology, a limited knowledge on the molecular machinery operating at the nanoscale has so far disallowed to control the reaction outcome. In this work, we show that the strength of the PAH-substrate interaction rules the competitive reaction pathways (cyclodehydrogenation versus dehydrogenative polymerisation). So, starting from the same molecular precursor and controlling its diffusion by the nature of the supporting surface, temperature-triggered dehydrogenation takes place to provide molecular or polymeric structures of variable dimensionality. We combined advanced in-situ surface techniques as STM and NEXAFS with theoretical ab-initio calculations to achieve a complete understanding of the self-assembling of molecular precursors on surfaces. Herein, by merging information from these techniques and different single-crystal metal substrates, we report on the diffusion control of competitive intramolecular and intermolecular dehydrogenative processes respectively called cyclodehydrogenation and dehydrogenative polymerisation, which operate in the on-surface synthesis of N-doped fullerene, nanographene, polyaromatic network, membrane or graphene (Fig. 1). By choosing the appropriate N-heteroaromatic precursors and by controlling their diffusion, the on-surface (cyclo)dehydrogenation can either lead to monomolecular triazafullerenes and diazahexabenzocoronenes (N-doped nanographene), or to N-doped polymeric networks.N