Decisive influence of substitution positions in molecular self-assembly.

Molecular self-assembly provides a versatile tool for creating functional molecular structures at surfaces. A rational design of molecular structure formation requires not only an in-depth understanding of the subtle balance between intermolecular and molecule-surface interactions, but might also involve considering chemical changes of the molecules, such as deprotonation. Here, we present a systematic investigation of a comparatively simple class of molecules, namely dihydroxybenzoic acid, which, nevertheless, enables creating a rich variety of structures when deposited onto calcite (10.

Substrate templating guides the photoinduced reaction of C60 on calcite.

A substrate-guided photochemical reaction of C60 fullerenes on calcite, a bulk insulator, investigated by non-contact atomic force microscopy is presented. The success of the covalent linkage is evident from a shortening of the intermolecular distances, which is clearly expressed by the disappearance of the moiré pattern. Furthermore, UV/Vis spectroscopy and mass spectrometry measurements carried out on thick films demonstrate the ability of our setup for initiating the photoinduced reaction.

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.

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

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.

Controlling molecular self-assembly on an insulating surface by rationally designing an efficient anchor functionality that maintains structural flexibility.

Molecular self-assembly on surfaces is dictated by the delicate balance between intermolecular and molecule-surface interactions. For many insulating surfaces, however, the molecule-surface interactions are weak and rather unspecific. Enhancing these interactions, on the other hand, often puts a severe limit on the achievable structural variety.

Molecular self-assembly on an insulating surface: interplay between substrate templating and intermolecular interactions.

We report on molecular self-assembly of biphenyl-4,4'-dicarboxylic acid (BPDCA) on CaCO3(1014) under ultra-high vacuum conditions. Two-dimensional, ordered islands are obtained upon deposition at room temperature, coexisting with a streaky structure that is ascribed to individual, mobile molecules forming a two-dimensional gas-like phase. High-resolution non-contact atomic force microscopy (NC-AFM) images of the molecular islands reveal an ordered inner structure that is dominated by rows of molecules aligned side by side running along the [4261] crystallographic direction.

Direct visualization of molecule deprotonation on an insulating surface.

Elucidating molecular-scale details of basic reaction steps on surfaces is decisive for a fundamental understanding of molecular reactivity within many fields, including catalysis and on-surface synthesis. Here, the deprotonation of 2,5-dihydroxybenzoic acid (DHBA) deposited onto calcite (101;4) held at room temperature is followed in situ by noncontact atomic force microscopy. After deposition, the molecules form two coexisting phases, a transient striped phase and a stable dense phase.

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 (CaCO(3))(10 ̅14) 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 CaCO(3)(10 ̅14) in the [01 ̅10] direction, while a lattice mismatch along the [ ̅4 ̅261] direction results in a large-scale moiré modulation.

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.