Molecular chirality at surfaces

Abstract

With the adsorption of larger molecules being increasingly tackled by surface scientists, the aspect of chirality often plays a role. This paper gives a topical review of molecular chirality at surfaces and gives a phenomenological overview of different aspects of adsorption and self‐assembly of chiral and prochiral molecules and the principles of mirror‐symmetry breaking at a surface. After a brief introduction into the history of molecular chirality and the important role it played for understanding the spatial structure of molecules, definitions of chirality are presented. Topics treated here are principle ways to create single chiral adsorbates, chiral ensembles, and monolayers by achiral molecules, adsorption of intrinsically chiral molecules at achiral and chiral surfaces, long‐range symmetry breaking in two‐dimensional (2D) crystals due to additional chiral bias, chiral restructuring of solid surfaces under the influence of chiral molecules, switching the handedness of adsorbates, and chirality at the liquid/air interface. An outlook onto further potential research directions and recommendations for further reading, including nonsurface‐related sources of chiral topics completes this paper.

From Homochiral Clusters to Racemate Crystals: Viable Nuclei in 2D Chiral Crystallization

“…14 As stable nuclei, homochiral quadruplets were identified on Cu(100), dominating as structural motifs throughout the crystal growth. In all cases [7]H was found to be adsorbed with the terminal phenanthrene group parallel to the surface.…”

“…7 Aside from crystallization, 8 how chiral information can propagate on a surface from a single molecule into supramolecular chiral structures is also relevant for technological processes such as performance of liquid crystals 9 and heterogeneous enantioselective catalysis. 10 By using scanning tunneling microscopy (STM), we have shown recently that pure enantiomers as well as racemic (rac) mixtures of the helically shaped aromatic heptahelicene ( [7]H, C30H18, Fig. 1) basically generate identical 2D crystal structures on the threefold symmetric fcc(111) surfaces of Cu, Ag and Au.…”

Giant Nonlinear Optical Activity of Achiral Origin in Planar Metasurfaces with Quadratic and Cubic Nonlinearities

“…[ 4,5 ] As the two manifestations of optical activity, optical rotatory dispersion and circular dichroism (CD) arise from phase and absorption differences between left-and rightcircularly polarized light (LCP and RCP, respectively), when they pass through the chiral media. Usually, these two effects are very weak in natural materials.…”

“…This geometry allows access to nonlinear susceptibility tensor components with one or several z indices, which can be quite large in some materials. [ 4,5 ] In particular, the so-called chiral tensor components contain such z indices. Since we seek to minimize the chiral contribution to SHG-CD and to emphasize an achiral SHG-CD instead, here, we use a femtosecond laser beam under normal incidence to the sample surface to interact with the nanostructures.…”

Affecting surface chirality via multicomponent adsorption of chiral and achiral molecules

“…Given that the energy of a CH-p contact is on average 0.8 kcal mol À1 , 13 the difference in stability between the two assemblies is consistent with the key role of this specific interaction of the chiral groups with the surface. 14 In conclusion, the impact of an achiral nucleobase (thymine) on the self-assembly of achiral and chiral OPV derivatives was systematically studied by means of STM and force field simulations at the liquid/solid interface. The nucleobase-induced pattern transformation of OPV derivatives from rosettes to dimers was observed.…”