A Multivalent Hexapod: Conformational Dynamics of Six-Legged Molecules in Self-Assembled Monolayers at a Solid−Liquid Interface

Abstract

A molecular hexapod having a benzene core and six oligo(p-phenylene vinylene) (OPV) legs is an ideal system to probe various types of (intramolecular) dynamics of individual molecules in physisorbed self-assembled monolayers at a solid-liquid interface. Scanning tunneling microscopy reveals that molecules adsorb in 2D crystalline as well as disordered domains. Strikingly, not all molecules have the six OPV units in contact with the graphite substrate: 4% of the molecules in the 2D crystalline domains and up to 80% of the molecules in the disordered domains have one or two OPV units desorbed. In addition, the presence of such a defect promotes the coexistence of another defect adjacent to it. Time-dependent STM experiments and molecular dynamics simulations reveal in detail the different dynamics involved and the multivalent nature of the interactions between hexapod and surface.

Hydrogen Bonding Versus van der Waals Interactions: Competitive Influence of Noncovalent Interactions on 2D Self‐Assembly at the Liquid–Solid Interface

“…Examples of similar discontinuous lamellar structures can be traced back to the early STM inves- tigations on alkylated cyanobiphenyl molecules. The monolayers formed by these liquid-crystalline molecules on atomically flat conductive surfaces such as HOPG [42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60] and/or MoS 2 [54,59,60] were the centre of focus in many of the early STM investigations. Periodic dislocations observed in the crystal structures were explained on the basis of strong molecule-substrate interactions and the registry mechanism of the alkyl chains with the underlying substrate.…”

“…[35] The solvent also enables adsorption-desorption dynamics, thereby affecting the mobility of the molecules at the liquid-solid interface. [43] The two solvent parameters that possibly govern this dynamics are solvation energy and solvent viscosity. [44,45] The solvent-induced polymorphism, effect of co-adsorption as well as the solvent effects on chirality and electronic structures have been summarised recently.…”

Dynamics in Self-assembled Organic Monolayers at the Liquid/Solid Interface Revealed by Scanning Tunneling Microscopy

“…3A) that acts as molecular 'hexapod' in a self-assembled monolayer at the 1-phenyloctane/ HOPG interface. [52][53][54] Structurally defect-free 2D crystalline domains covering large areas are not observed though often 'disordered' domains are observed in the midst of or between these small crystalline domains. We identify a group of molecules as belonging to a disordered domain if the centres of the molecules are not on top of 2D crystalline lattice points within a given area or if the molecules have a different orientation than those in the crystalline matrix.…”

Molecular Dynamics in Two-Dimensional Supramolecular Systems Observed by STM

“…An excellent example of such conformational dynamics was reported by De Feyter and coworkers [43]. A molecular hexapod, which has a benzene core and six oligo( p -phenylene vinylene) legs (Figure 10 left), formed 2D crystalline structures at the 1-phenyloctane–HOPG interface predominantly.…”