Spontaneous Transmission of Chirality through Multiple Length Scales

Abstract

The hierarchical transfer of chirality in nature, from the nano-, to meso-, to macroscopic length scales, is very complex, and as of yet, not well understood. The advent of scanning probes has allowed chirality to be monitored at the single molecule or monolayer level and has opened up the possibility to track enantiospecific interactions and chiral self-assembly with molecular-scale detail. This paper describes the self-assembly of a simple, model molecule (naphtho[2,3-a]pyrene) that is achiral in the gas phase, but becomes chiral when adsorbed on a surface. This polyaromatic hydrocarbon forms a stable and reversibly ordered system on Cu(111) in which the transmission of chirality from single surface-bound molecules to complex 2D chiral architectures can be monitored as a function of molecular packing density and surface temperature. In addition to the point chirality of the surface-bound molecule, the unit cell of the molecular domains was also found to be chiral due to the incommensurate alignment of the molecular rows with respect to the underlying metal lattice. These molecular domains always aggregated in groups of three, all of the same chirality, but with different rotational orientations, forming homochiral "tri-lobe" ensembles. At a larger length scale, these tri-lobe ensembles associated with nearest-neighbor tri-lobe units of opposite chirality at lower packing densities before forming an extended array of homochiral tri-lobe ensembles at higher converges. This system displayed chirality at a variety of size scales from the molecular (≈1 nm) and domain (≈5 nm) to the tri-lobe ensemble (≈10 nm) and extended array (>25 nm) levels. The chirality of the tri-lobe ensembles dictated how the overall surface packing occurred and both homo- and heterochiral arrays could be reproducibly and reversibly formed and interchanged as a function of surface coverage. Finally, these chirally templated surfaces displayed remarkable enantiospecificity for naphtho[2,3-a]pyrene molecules adsorbed in the second layer. Given its simplicity, reversibility, and rich degree of order, this system represents an ideal test bed for the investigation of symmetry breaking and the hierarchical transmission of chirality through multiple length scales.

Through-space transfer of chiral information mediated by a plasmonic nanomaterial

“…In contrast, our modelling shows that a through-bond mechanism is not responsible for our SERROA results, and our chiral analyte is around 50 bonds from the metal surface, confirming that our chirality transfer phenomenon is a fundamentally different process to that reported by Cao and co-authors. Chirality transfer is a broad topic, and our results also appear to fundamentally differ from the electro-magnetic field (EM)-induced torsional perturbations in metamaterials consisting of pairs of split Cu-rings, which was reported by Liu and colleagues 39 , and also from the transmission of chirality from single surface-bound molecules to complex chiral arrays through increasing molecular coverage on an ordered Cu(111) surface, as observed by Iski and co-authors 40 .…”

Pyrene-functionalized organogel and spacer effect: from emissive nanofiber to nanotube and inversion of supramolecular chirality

“…18 Thus, among all of the properties of self-assembled systems, supramolecular chirality is one of the most sensitive factors reecting the arrangement of the building blocks, because supramolecular chirality is a result of the asymmetric arrangement of the molecules in a non-covalent assembly. 19,20 In general, during the assembly process, the chiral information is directly transformed from the molecular building blocks to the suprastructures, [21][22][23] and thus the supramolecular chirality basically depends on the molecular chirality, i.e. if one enantiomer gives a right-handed assembly, the other would provide a le-handed one.…”

Designing enantioselectivity in chiral self-assembly at a solid substrate: a theoretical study of competing interactions

“…Chirality is ubiquitous on surfaces, as many molecules that are achiral in solution become chiral when bound to a surface, by participating in chiral adsorbed supramolecular structures. 5,6 Moreover, chiral molecules that do not undergo enantiospecic crystallization may form extended homochiral structures when self-assembled at a solid surface. [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] An underlying surface breaks the symmetry of interacting pairs of molecules, and may also alter their preferred positions and orientations.…”

“…Besides the more obvious implications for direct separation of enantiomers, this behavior has applications in the molecular design of surfaces for chromatography, chiral catalysis, chiral sensing, the synthesis of nonlinear optical materials and organic chiral nanotubes. [2][3][4][5]11,[14][15][16][25][26][27][28][29] In order to gain experimental control over chiral self-assembly outcomes, a clearer understanding of the complex effects governing the formation of chiral patterns is necessary. Of particular interest is the interplay between intermolecular and molecule-substrate interactions and associated kinetic and thermodynamic effects.…”