Two-dimensional organisational chirality through supramolecular assembly of molecules at metal surfaces

Abstract

Although the concept of molecular chirality was enunciated by Pasteur in 1848, it is only very recently that the creation of chirality at two-dimensional surfaces is being mapped and understood. In many systems, the manifestation of surface chirality is driven by supramolecular chemistry, or `chemistry beyond the covalent bond', where assemblies of molecules held together by non-covalent intermolecular interactions, lead to structures that possess no inversion symmetry elements and are, thus, able to exist in two distinguishable mirror, or enantiomeric, forms. Here, we highlight some of the ways in which chiral organisations are created at surfaces, with examples of structures ranging from 1D chains, to nanoscale 2D clusters and, finally, to large, macroscopic 2D chiral arrays. Wherever possible, we have emphasised the various driving forces that govern the creation of chiral structures; in particular the balance between the metal–molecule interaction and the soft supramolecular interactions that drive chiral self-assembly at metal surfaces. These examples illustrate that surface chiral systems not only exploit the full gamut of already identified supramolecular interactions, but also uniquely include the additional supramolecular forces mediated by through-metal interactions. Finally, since many of the systems exploit complex organic molecules to introduce the chirality function, the need to understand fully the nature of the adsorbate, its bonding to the surface and its communication to neighbouring molecules is highlighted as a prime need in this area if one wishes to capture the essence of the balances that induce and propagate chirality.