Self‐Assembly of Decoupled Borazines on Metal Surfaces: The Role of the Peripheral Groups

Abstract

Two borazine derivatives have been synthesised to investigate their self-assembly behaviour on Au(111) and Cu(111) surfaces by scanning tunnelling microscopy (STM) and theoretical simulations. Both borazines form extended 2D networks upon adsorption on both substrates at room temperature. Whereas the more compact triphenyl borazine 1 arranges into close-packed ordered molecular islands with an extremely low density of defects on both substrates, the tris(phenyl-4-phenylethynyl) derivative 2 assembles into porous molecular networks due to its longer lateral substituents. For both species, the steric hindrance between the phenyl and mesityl substituents results in an effective decoupling of the central borazine core from the surface. For borazine 1, this is enough to weaken the molecule–substrate interaction, so that the assemblies are only driven by attractive van der Waals intermolecular forces. For the longer and more flexible borazine 2, a stronger molecule–substrate interaction becomes possible through its peripheral substituents on the more reactive copper surface.

BN‐Patterning of Metallic Substrates through Metal Coordination of Decoupled Borazines

“…In particular, precisely tailored substituents of molecules can be utilized to realize targeted adsorption geometries, as well as to preserve the intrinsic properties of molecules upon adsorption on a metal support . Recently, it has been proposed that the borazine scaffold of a molecule can be protected and electronically decoupled from the conductive substrate by di‐methylphenyl terminal groups through steric hindrance without affecting the possibility of the molecule itself to adsorb and self‐assemble . Additionally, the selection of the substituent's termination (e.g.…”

“…Specifically, the three prominent lobes observed in STM can be reasonably associated with the bulky di‐methyl‐bearing aryl rings. This assignment is in line with STM observations and complementary molecular dynamics (MD) modeling reported for dimethyl‐bearing aryl borazine derivatives on Au(111) and Cu(111) . Consistently, we observe a very similar intramolecular contrast featuring three bright protrusions for BNAPy on Cu(111) (see Figure ).…”

“…The molecules, deposited onto the sample held at room temperature, arrange in six‐membered rings and form porous honeycomb networks. A similar self‐assembly was observed for related molecules on the Au(111) surface . Molecular domains with sizes of several hundreds of nm and arbitrary orientation with respect to the crystal high‐symmetry directions were present on the samples.…”

“…Our STS data on BNPPy and BNAPy molecules (Figures and S32) reveal that the surface state feature is still detected on the molecular core on both the Cu(111) and the Ag substrates. This observation shows that the borazine core is decoupled from the metallic substrates by means of the dimethyl substituents, a fact which has been anticipated for similar borazine derivatives in a previous report . Additionally, the XPS binding energy of the N 1s line is at 399.2 eV, comparable to the value reported for other borazine derivatives on noble metal supports, and exceeding the value for h ‐BN/Cu(111) by about 1 eV .…”

“…[11] Recently,i th as been proposed that the borazine scaffold of am olecule can be protected and electronically decoupled from the conductive substrate by dimethylphenyl terminal groups through steric hindrance without affecting the possibility of the molecule itself to adsorb and self-assemble. [12] Additionally,t he selection of the substituent's termination (e.g. -carbonitrile (CN), -carboxylate, -pyridyl) steers the supramolecular interactions, driving for example the formation of two dimensional metal-organic coordinationn etworks (2D-MOCNs) in the presence of metal adatoms.…”