Substrate templating upon self-assembly of hydrogen-bonded molecular networks on an insulating surface.

M olecular self-assembly on insulating surfaces, despite being highly relvant to many applications, generally suffers from the weak molecule–surface interactions present on dielectric surfaces, especially when benchmarked against metallic substrates. Therefore, to fully exploit the potential of molecular self-assembly, increasing the infl uence of the substrate constitutes an essential prerequisite. Upon deposition of terephthalic acid and trimesic acid onto the natural cleavage plane of calcite, extended hydrogen-bonded networks are formed, which wet the substrate. The observed structural complexity matches the variety realized on metal surfaces. A detailed analysis of the molecular struct…

Atomic-resolution imaging of clean and hydrogen-terminated C(100)-(2×1)diamond surfaces using noncontact AFM

Received 22 April 2010; published 14 May 2010High-purity, type IIa diamond is investigated by noncontact atomic force microscopy NC-AFM .Wepresent atomic-resolution images of both the electrically conducting hydrogen-terminated C 100 - 2 1 :Hsurface and the insulating C 100 - 2 1 surface. For the hydrogen-terminated surface, a nearly square unitcell is imaged. In contrast to previous scanning tunneling microscopy experiments, NC-AFM imaging allowsboth hydrogen atoms within the unit cell to be resolved individually, indicating a symmetric dimer alignment.Upon removing the surface hydrogen, the diamond sample becomes insulating. We present atomic-resolutionimages, revealing individual C-C dim…

On-surface covalent linking of organic building blocks on a bulk insulator.

On-surface synthesis in ultrahigh vacuum provides a promising strategy for creating thermally and chemically stable molecular structures at surfaces. The two-dimensional confinement of the educts, the possibility of working at higher (or lower) temperatures in the absence of solvent, and the templating effect of the surface bear the potential of preparing compounds that cannot be obtained in solution. Moreover, covalently linked conjugated molecules allow for efficient electron transport and are, thus, particularly interesting for future molecular electronics applications. When having these applications in mind, electrically insulating substrates are mandatory to provide sufficient decoupli…

Racemic and Optically Pure Heptahelicene-2-carboxylic Acid: Its Synthesis and Self-Assembly into Nanowire-Like Aggregates

Heptahelicene-2-carboxylic acid was effectively synthesised from suitably functionalised naphthalene building blocks. Methoxy-substituted 1,1'-ethyne-1,2-diylbis(2-but-3-yn-1-ylnaphthalene) was cyclised in the presence of CpCo(CO)(2)/PPh(3) to 2-methoxy-7,8,11,12-tetrahydroheptahelicene, which was converted into heptahelicen-2-yl trifluoromethanesulfonate. This reactive intermediate underwent Pd(OAc)(2)/dppp-catalysed methoxycarbonylation reaction to provide, after hydrolysis, heptahelicene-2-carboxylic acid. The racemate was resolved into enantiomers by semipreparative HPLC on a chiral column. The helicity of (+)-(P)-heptahelicene-2-carboxylic acid was assigned by correlating its CD spectr…

Racemic and Optically Pure Heptahelicene-2-carboxylic Acid: Its Synthesis and Self-Assembly into Nanowire-Like Aggregates (Eur. J. Org. Chem. 5/2011)

The cover picture shows heptahelicene-2-carboxylic acid, whose synthesis and self-assembly are central to the article. The background features Prague's riverbank, which is intermixed with the nanowire-like aggregates of heptahelicene-2-carboxylic acid. The alignment of the swans makes the link between self-assembly and the Prague view. Details are discussed in the article by I. G. Stara, I. Starý, A. Kuhnle et al. on p. 853 ff. Background photo by M. Bělohradský.

Templating: Substrate Templating upon Self-Assembly of Hydrogen-Bonded Molecular Networks on an Insulating Surface (Small 19/2012)

Molecular Self-Assembly of Enantiopure Heptahelicene-2-Carboxylic Acid on Calcite (1014)

Chirality can have a decisive influence on the molecular structure formation upon self-assembly on surfaces. In this paper, we study the structures formed by enantiopure (M)-heptahelicene-2-carboxylic acid ((M)-[7]HCA) on the calcite (10 (1) over bar4) cleavage plane under ultrahigh vacuum conditions. Previous noncontact atomic force microscopy studies have revealed that the racemic mixture of (M)-[7]HCA and (P)-[7]FICA (1:1) self-assembles into well-defined molecular double rows that are oriented along the calcite [01 (1) over bar0] direction. Here, we investigate the enantiopure (M)[7]HCA compound, resulting in distinctly different molecular structures upon deposition onto calcite (10 (1)…

Growth kinetics of racemic heptahelicene-2-carboxylic acid nanowires on calcite (104).

Molecular self-assembly of racemic heptahelicene-2-carboxylic acid on a dielectric substrate at room temperature can be used to generate wire-like organic nanostructures consisting of single and double molecular rows. By means of non-contact atomic force microscopy, we investigate the growth of the wire-like pattern after deposition by experimental and theoretical means. From analyzing the time dependence of the mean row length, two distinct regimes were found. At the early post-deposition stage, the mean length grows in time. Subsequently, a crossover to a second regime is observed, where the mean row length remains nearly constant. We explain these findings by a mean-field rate equation a…

From dewetting to wetting molecular layers: C60 on CaCO3(10 ̅14) as a case study.

We report the formation of extended molecular layers of C-60 molecules on a dielectric surface at room temperature. In sharp contrast to previous C-60 adsorption studies on prototypical ionic crystal surfaces, a wetting layer is obtained when choosing the calcite (CaCO3)(10 (1) over bar4) surface as a substrate. Non-contact atomic force microscopy data reveal an excellent match of the hexagonal lattice of the molecular layer with the unit cell dimension of CaCO3(10 (1) over bar4) in the [01 (1) over bar0] direction, while a lattice mismatch along the [(4) over bar(2) over bar 61] direction results in a large-scale moire modulation. Overall, a (2 x 15) wetting layer is obtained. The distinct…

Controlled Activation of Substrate Templating in Molecular Self-Assembly by Deprotonation

cited By 7; International audience; Templated assembly of organic molecules constitutes a promising approach for fabricating functional nanostructures at surfaces with molecular-scale control. Using the substrate template for steering the adsorbate growth enables creating a rich variety of molecular structures by tuning the subtle balance of intermolecular and molecule–surface interactions. On insulating surfaces, however, surface templating is largely absent due to the comparatively weak molecule–surface interactions compared to metallic substrates. Here, we demonstrate the activation of substrate templating in molecular self-assembly on a bulk insulator by controlled deprotonation of the …

Sequential and site-specific on-surface synthesis on a bulk insulator

cited By 15; International audience; The bottom-up construction of functional devices from molecular building blocks offers great potential in tailoring materials properties and functionality with utmost control. An important step toward exploiting bottom-up construction for real-life applications is the creation of covalently bonded structures that provide sufficient stability as well as superior charge transport properties over reversibly linked self-assembled structures. On-surface synthesis has emerged as a promising strategy for fabricating stable, covalently bound molecular structure on surfaces. So far, a majority of the structures created by this method have been obtained from a rat…

Tuning molecular self-assembly on bulk insulator surfaces by anchoring of the organic building blocks.

Molecular self-assembly constitutes a versatile strategy for creating functional structures on surfaces. Tuning the subtle balance between intermolecular and molecule-surface interactions allows structure formation to be tailored at the single-molecule level. While metal surfaces usually exhibit interaction strengths in an energy range that favors molecular self-assembly, dielectric surfaces having low surface energies often lack sufficient interactions with adsorbed molecules. As a consequence, application-relevant, bulk insulating materials pose significant challenges when considering them as supporting substrates for molecular self-assembly. Here, the current status of molecular self-ass…

Influence of charge transfer doping on the morphologies of C60islands on hydrogenated diamond C(100)-(2×1)

The adsorption and island formation of C${}_{60}$ fullerenes on the hydrogenated C(100)-($2\ifmmode\times\else\texttimes\fi{}1$):H diamond surface is studied using high-resolution noncontact atomic force microscopy in ultrahigh vacuum. At room temperature, C${}_{60}$ fullerene molecules assemble into monolayer islands, exhibiting a hexagonally close-packed internal structure. Dewetting is observed when raising the substrate temperature above approximately 505 K, resulting in two-layer high islands. In contrast to the monolayer islands, these double-layer islands form extended wetting layers. This peculiar behavior is explained by an increased molecule-substrate binding energy in the case of…