Conservation of Chirality in a Hierarchical Supramolecular Self‐Assembled Structure with Pentagonal Symmetry

Abstract

Nested assembly: Chiral molecules of 5,6,11,12‐tetraphenylnaphthacene (rubrene) organize spontaneously into homochiral supramolecular architectures of increasing complexity. Adsorbed individual molecules self‐assemble enantioselectively into chiral pentagonal supermolecules, which act as building blocks for the formation of chiral supramolecular decagons (see STM images).

Molecular Assembly of Rubrene on a Metal/Metal Oxide Nanotemplate

“…46 Scanning tunneling microscopy (STM) studies of rubrene on Au(111) carried out at 5 K demonstrated that the twisted conformation of the molecule and its chirality are retained upon physisorption and can be exploited to drive the assembly of exotic chiral hierarchical supramolecular structures. 47 STM investigations were carried out also on single-crystal surfaces in ambient air and revealed a herringbone-like motif similar to that found in the bulk. 48 In this paper, we investigate the adsorption and self-assembly properties of rubrene molecules on the O-Cu nanotemplate by in situ high-resolution STM in UHV.…”

Self-assembly of Rubrene on Copper Surfaces

“…48 The STM images obtained on Cu(100) suggest that the tetracene backbone of the molecule lies parallel to the surface. To gain further insight into the molecules' conformation we analyzed series of apparent height profiles of the phenyl substituents of rubrene molecules adsorbed on Cu(100).…”

“…40 The excellent charge transport properties of rubrene have motivated several fundamental studies of rubrene single crystals, [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42] thin films, [43][44][45][46][47] and self-assembled structures. 28,[48][49][50] Rubrene is a nonplanar and flexible molecule consisting of a tetracene backbone with two pairs of phenyl substituents symmetrically attached on either side of the backbone ( Figure 1). The intramolecular steric hindrance between the phenyl substituents results in a significant strain within the molecule, which can be released by either a twisting of the tetracene backbone as seen in the gas phase geometry (Figure 2, conformation A), or by an out-of-plane distortion of the phenyl substituents seen in the single crystal geometry (Figure 2, conformation B).…”

“…This change is induced by the increased contribution of the rubrene lattice, which supplies the energy for backbone planarization. The selfassembly of rubrene has recently been studied by scanning tunneling microscopy (STM) on Au(111) at 5 K. 48 These studies suggested that, upon adsorption, the molecule maintains its twisted conformation and therefore its chirality. Further studies demonstrated that rubrene on Au(111) exhibits adsorption geometries with differing electronic properties.…”

Molecular chirality at surfaces

“…A similar apolar intrinsically chiral molecule, the aromatic 5,6,11,12-tetraphenyltetracene (rubrene, Fig. 21), however, shows a remarkable hierarchical homochiral recognition [133]. The molecule is another example of a chiral structure due to steric overcrowding and the absence of a stereogenic center.…”