Two dimensional self-assembled molecular networks via on surface reactions

The discovery of graphene and its remarkable properties have given rise to an increased interest of the scientific community towards the field of carbon-based electronics. In order to overcome the limitation of graphene's metallic character, several routes have been considered, such as chemical decoration, substrate-induced bandgap opening or doping with boron and/or nitrogen atoms, by creating a hybrid graphene-h-BN two-dimensional material. Surface-assisted synthesis offers the possibility of creating organic analogues of graphene with high electron mobility and tunable bandgaps. Two-dimensional molecular networks or polymers can be obtained through bottom-up synthesis methods, where the building blocks - small organic molecules - have the potential of tuning the desired properties of the covalent molecular network. The field of synthesizing hybrid boron nitride-carbon 2D covalent molecular networks, that can create a graphene-like 2D material, via surface reactions is still incipient, while their electronic properties remain yet unexplored. Moreover, no studies of the synthesis of chiral covalent 2D molecular networks, which can allow their usage in enantiospecific applications have been reported up to date. This thesis is focused on synthesizing carbon-boron nitride 2D molecular networks using surface assisted reactions, namely the Ullmann coupling reaction of brominated borazatruxenes as well as the B3N3 ring closure reaction of isodiaminodiborane precursors. The electronic properties and assembly of borazatruxene, a new class of BN-doped polycyclic aromatic hydrocarbon, and its comparison with truxene, its organic counterpart, shows that the inclusion of the BN ring in borazatruxene increases its electronic bandgap. A hierarchical mechanism based on chiral homodimer units of 3Br-borazatruxene towards the formation of 1D chains and 2D H bonded networks is discussed. This mechanism is key for homochiral segregation into large chiral domains, which allow the formation of chiral borazatruxene-based covalent molecular networks. The obtained 3Br-borazatruxene H-bonded networks present low symmetry, which allowed the formation of small pores able to trap atoms or small molecular species. Theoretical predictions show that up to two Na atoms could be trapped within these pores, inducing hybrid Na-C bands with anisotropic dispersion. Subsequently, the on-surface Ullmann coupling of 3Br-borazatruxene precursors on Au(111), starting from the H-bonded proto-stage discussed above is investigated. We obtained the first chiral 3Br-borazatruxene macrocycles on Au(111), whose electronic properties are investigated by scanning tunneling spectroscopy dI/dV measurements. In order to improve the quality of the network, we employ the gradual dehalogenation process of this precursor on Au(111), along with the homodimer-based low symmetry of the H-bonded network, leading to the description of a two-stage Ullmann reaction of 3Br-borazatruxenes. The final part of the thesis is focused on the B₃N₃ ring closure reaction of isodiaminodiborane (IDADB) on Au(111), as a new surface-asissted reaction for obtaining B₃N₃-C molecular networks. Temperature-dependent XPS studies have shown the successful formation of closed B3N3 rings by investigating the chemical fingerprints of B, N and C 1s and via STM imaging investigations of the formed covalent assemblies. Building on the experimental results, a mechanism of the surface-assisted BN ring closure of isodiaminodiborane on Au(111) is proposed.