Chiral Ordering and Conformational Dynamics for a Class of Oligo-phenylene-ethynylenes on Au(111)

Abstract

Adsorption structures formed from a class of planar organic molecules on the Au(111) surface under ultrahigh vacuum conditions have been characterized using scanning tunneling microscopy (STM). The molecules have different geometries, linear, bent, or three-spoke, but all consist of a conjugated aromatic backbone formed from three or four benzene rings connected by ethynylene spokes and functionalized at all ends with an aldehyde, a hydroxyl, and a bulky tert-butyl group. Upon adsorption, the molecules adopt different surface conformations some of which are chiral. For the majority of the observed adsorption structures, chirality is expressed also in the molecular tiling pattern, and the two levels of chirality display a high degree of correlation. The formation and chiral ordering of the self-assembled structures are shown to result from dynamic interchanges between a diffusing lattice gas and the nucleated islands, as well as from a chiral switching process in which molecules alter their conformation by an intramolecular rotation around a molecular spoke, enabling them to accommodate to the tiling pattern of the surrounding molecular structures. The kinetics of the conformational switching is investigated from time-resolved, variable temperature STM, showing the process to involve an activation energy of approximately 0.3 eV depending on the local molecular environment. The molecule-molecule interactions appear primarily to be of van der Waals character, despite the investigated compounds having functional moieties capable of forming intermolecular hydrogen bonds.

Self-assembly of Rubrene on Copper Surfaces

“…We do not observe isolated molecules outside of the molecular ensembles, which is further evidence that any molecules not contained in the structured islands are highly diffusive. 60,61 Islands are observed after a threshold coverage of approximately 0.7 monolayers (ML) is reached. Similar behavior has been observed for other π-conjugated hydrocarbons on other metallic surfaces, for example, perylene on Ag(110) 62 and Cu(100), 56 coronene on Cu(100), 63 and complex helical molecules such as heptahelicene on Cu(111).…”

Imaging on-surface hierarchical assembly of chiral supramolecular networks

“…As mentioned above, for the system considered in this study, above RT, the large structural fluctuations combined with a lack of qualitative evolution over long times (up to few days) indicate that the equilibrium condition has been reached. 50,51,62 This allows exploiting the IRT maps to estimate the binding energy difference between the homo-and heterochiral configurations. In fact, assuming the activation entropy to be the same for the two attachment processes, the ratio of the probability distribution can be expressed as:…”

Structure and structural transition of chiral domains in oligo(p-phenylenevinylene) assembly investigated by scanning tunneling microscopy

“…Among various molecular nanostructures, two-dimensional surface chirality is a property of asymmetry and of great interest in fundamental research and industrial application such as life genesis, nonlinear optics, enantioselective heterogeneous catalysis, and surface modification (1)(2)(3). With atomic resolution, scanning tunneling microscopy (STM) is powerful in surface chirality study (4)(5)(6)(7). From absolute chirality determination to chiral structure fabrication with chiral molecules or achiral molecules on a solid surface, a few results have been reported (8)(9)(10)(11)(12)(13).…”