A work aimed to obtain porous nanographenes in order to study the electronic properties of such exotic nanostructure allows unveils a new chemical reaction.
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Artistic representation of porous nanographenes on gold. / © Eugenio Vázquez (CiQUS) |
This work published in Nano Latters is a collaboration involving three groups in Spain: (1) the team formed by Diego Peña, Enrique Guitián and Manuel Vilas at CiQUS (Universidade de Santiago de Compostela) specialized in organic chemistry; (2) the group led by Jose Ignacio Pascual, experts in the field of Scanning Tunnelling Microscopy (STM) working in nanoGUNE (San Sebastián, Spain); (3) Aran García-Leuke at DIPC (San Sebastián) in charge of the calculations.
The initial goal of this work was to obtain porous nanographenes in order to study the electronic properties of such exotic nanostructures. First, the chemistry group at CiQUS synthesized a polycyclic aromatic compound decorated with two bromine atoms forming 60º between them. Then, the physics group at nanoGUNE deposited the molecules on a gold surface, and heat to induce an Ullmann-type coupling.
Based on the relative position of the bromine atoms, it was expected to obtain a trimer with an 18-annulene core in the centre. Meanwhile, the group at DIPC simulated the electronic properties of this porous nanographene. The technique chosen to visualise the products of the on-surface reactions was high resolution STM with CO tips under ultrahigh vacuum conditions and very low temperature. This is an extremely powerful technique with submolecular resolution.
Satisfyingly, STM analysis confirmed the formation of porous nanographenes on gold surface. However, it also revealed that an unexpected reaction had taken place in the graphene branches: the cyclodehydrogenation of non-planar conjoined cove regions to obtain azulene moieties (fused five-seven membered rings, which are flat). This reaction was never described before in the chemistry literature. Its discovery can be considered as a new example of serendipity, a major driven force in Science. This work is a good example of the potential of combining organic synthesis with high resolution STM to discover new unexpected reactions. In addition, it’s also a good example of the collaboration between chemists and physicists in the exciting new field of on-surface synthesis.