Speaker
Description
The formation of one- and two-dimensional (1D & 2D) molecular structures at the nanoscale rely on the self-assembly of organic molecules with interacting functional groups on solid single crystal substrates. Molecules containing aldehyde functional groups are promising candidates for the formation of 2D self-assembled networks and the subsequent formation of robust covalent networks [1,2].
We have studied the adsorption of a molecule with a pyrene core functionalized with four benzaldehyde groups on the Au(111) surface at room temperature using scanning tunneling microscopy (STM) and density functional (DFT) simulations. We identify several 1D and 2D molecular arrangements which depend on molecular coverage.
At low coverage, deposition yields a mixture of 1D and 2D molecular arrangements. The 1D structures are characterized by a periodic arrangement of molecules spaced 2.07 ± 0.01 nm apart. Our combined STM-DFT data indicate that the chains incorporate Au ad-atoms bridging between the aldehyde groups of adjacent molecules. The ab-initio simulation yields a stabilization energy of -4.65 eV/molecule with an intermolecular spacing of 2.03 nm in close agreement with experiment.
The 2D structure is a mix of regions of “stacked” self-assembly, and porous regions in which the stacked structure incorporates an ordered arrangement of molecular vacancies. STM and DFT indicates assembly is driven by the alignment of four aldehyde groups on neighbouring molecules.
At higher coverage, a staggered close-packed arrangement was formed led by hydrogen bonding between the oxygen atoms of the aldehyde groups and phenyl hydrogen of the adjacent molecules. DFT yields a stabilization energy of –4.57 eV/molecule.
Post annealing experiments were performed from room temperature up to 500 K in 25 K intervals to investigate the evolution of the structures. Some changes were observed and will be discussed. Most notable are changes in all the structures at 450 K which suggest chemical changes in the networks indicating the formation of 1D/2D covalent structures.
[1] Cao, N. et al. (2021), Nanoscale, 13, 19884.
[2] Díaz Arado, O. et al. (2015), Chem. Commun., 51, 4887.
| Keyword-1 | 2D Nanomaterials |
|---|---|
| Keyword-2 | Scanning Tunneling Microscopy |
| Keyword-3 | Molecular Self-Assembly |