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Tetrabromo aromatics can be synthesized by the Fischer-Zimmermann condensation of appropriate pyrylium salts with arylene dicarboxylic acid salts. Their cyclization by intramolecular Yamamoto coupling yields strained bicyclophanes with adjustable sizes and different intraannular bridges. All compounds adsorb at the solid/liquid interface on highly oriented pyrolytic graphite (HOPG) and are investigated by scanning tunneling microscopy (STM) with submolecular resolution. The observed two-dimensional (2D) supramolecular nanopatterns depend only on the sizes and alkoxy periphery of the cyclophanes and are independent of the specific structures of the intraannular bridges. Since the central arylene moieties of the smaller species are oriented perpendicular to the planes of the bicyclophanes, their substituents protrude from the surface by up to 1.6 nm after adsorption. Therefore, these molecules are attractive platforms for addressing the volume phase above the graphite surface.

Molecular spoked wheels with intraannular functionalizable pillars are synthesized in a modular approach. The functionalities at their ends are variable, and a propargyl alcohol, a [6,6]-phenyl-C61-butyrate, and a perylene monoimide are investigated. All compounds form two-dimensional crystals on highly oriented pyrolytic graphite at the solid-liquid interface. As determined by submolecularly resolved scanning tunneling microscopy, the pillars adopt equilibrium distances of 6.0 nm. The fullerene has a residual mobility, limited by the length of the flexible connector unit. The experimental results are supported and rationalized by molecular dynamics simulations. These also show that, in contrast, the more rigidly attached perylene monoimide units remain oriented along the surface normal and maintain a smallest distance of 2 nm above the graphite substrate. The robust packing concept also holds for cocrystals with molecular hexagons that expand the pillar-pillar distances by 15 % and block unspecific intercalation.

Molecular spoked wheels with D3h and Cs symmetry are synthesized by Vollhardt trimerization of C2v-symmetric dumbbell structures with central acetylene units and subsequent intramolecular ring closure. Scanning tunneling microscopy of the D3h-symmetric species at the solid/liquid interface on graphite reveals triporous chiral honeycomb nanopatterns in which the alkoxy side chains dominate the packing over the carboxylic acid groups, which remain unpaired. In contrast, Cs-symmetric isomers partially allow for pairing of the carboxylic acids, which therefore act as a probe for the reduced alkoxy chain nanopattern stabilization. This observation also reflects the adsorbate substrate symmetry mismatch, which leads to an increase of nanopattern complexity and unexpected templating of alkoxy side chains along the graphite armchair directions. State-of-the-art GFN-FF calculations confirm the overall structure of this packing and attribute the unusual side-chain orientation to a steric constraint in a confined environment. These calculations go far beyond conventional simple space-filling models and are therefore particularly suitable for this special case of molecular packing., Scanning tunneling microscopy investigations of phenylene-based molecular spoked wheels with D3h and Cs symmetries on graphite show the competitive or complementary effects of carboxylic acid groups and alkoxy chains on the nanopattern formation.

Alkyl- and alkoxy-substituted p-phenylene–butadiynylene tetramers, obtained via a stepwise synthesis, are polymerized under Glaser coupling conditions. The fractionation of the oligomers by recycling gel permeation chromatography (recGPC) yields three sets of monodisperse oligo(p-phenylene–butadiynylene)s (OPBs) with degrees of polymerization n = 4, 8, 12, ..., 60. Subsequent GPC analysis of these oligomers provides three sets of size- and substituent-dependent conversion factors that quantify the overestimation of the oligomer molecular weight when a polystyrene (PS) calibrated GPC system is used for the data analysis. Scanning tunneling microscopy (STM) of representative oligomers at the solid/liquid interface visualizes the monodispersity, the length-dependent rigidity, and their assembling behavior.

Alkoxy-substituted phenylene–ethynylene–butadiynylenes (PEBs) are connected via 1H-benzimidazole units to form H-shaped molecular scaffolds that self-assemble on graphite at the solid/liquid interface. Spacer lengths and end groups determine supramolecular tiling patterns, as shown via scanning tunneling microscopy (STM).

We employ five π-conjugated model materials of different molecular shape-oligomers and cyclic structures-to investigate the extent of exciton self-trapping and torsional motion of the molecular framework following optical excitation. Our studies combine steady state and transient fluorescence spectroscopy in the ensemble with measurements of polarization anisotropy on single molecules, supported by Monte Carlo simulations. The dimer exhibits a significant spectral red shift within ∼100 ps after photoexcitation which is attributed to torsional relaxation. This relaxation mechanism is inhibited in the structurally rigid macrocyclic analogue. However, both systems show a high degree of exciton localization but with very different consequences: while, in the macrocycle, the exciton localizes randomly on different parts of the ring, scrambling polarization memory, in the dimer, localization leads to a deterministic exciton position with luminescence characteristics of a dipole. Monte Carlo simulations allow us to quantify the structural difference between the emitting and absorbing units of the π-conjugated system in terms of disorder parameters.

Ga+ focused ion beam (FIB) patterning was used to structure highly oriented pyrolytic graphite surfaces with square, periodic arrays of amorphous carbon defects (mesh sizes: 300 nm–2 µm). Controlled oxygen etching of these arrays leads to matrices of uniform, orientationally aligned, nm-sized, hexagonal holes. The properties of the resulting hole assembly (hole depths and lateral hole dimensions) have been investigated by means of atomic force microscopy, scanning electron microscopy and FIB sectioning. The hole dimensions and uniformity both depend on the FIB parameters and etching conditions. Etching temperatures from 500 to 700 °C were applied. Initial etch rates of up to 106 C s−1 per individual hole were observed when using oxygen pressures of 200 mbar. For an etch temperature of 590 °C the rate of etching of individual holes was found to depend measurably on the inter-hole separation. This confirms that the associated reaction kinetics is mediated by the finite diffusion length of reactive oxygen species along the graphite basal plane. Prolonged etching results in hole–hole contact and generation of mesa arrays of controllable size and shape.

Rigid rod oligo(phenylene-ethynylene-butadiynylene)s (oPEBs), “half-rings” of two rigid rods connected via a molecular clamp unit, and shape-persistent macrocycles (cyclic “half-ring dimers”) are synthesized and their self-assembled monolayers (SAMs) are investigated by scanning tunneling microscopy (STM) at the interface of 1,2,4-trichlorobenzene (TCB)/highly oriented pyrolytic graphite (HOPG). The results are important for the design of molecular building blocks for two-dimensional nanoscale architectures on solid surfaces.