Synthesis, Properties, and Two-Dimensional Adsorption Characteristics of [6]Hexahelicene-7-carboxylic acid.

A convergent synthesis of racemic [6]hexahelicene-7-carboxylic acid by cross-coupling of a bicyclic and a tricyclic component is described. A metal-catalyzed ring-closure is also a fundamental component of the synthetic approach. Scanning tunneling microscopy (STM) measurements of the racemate self-assembled on Au(111) at liquid-solid interface revealed the formation of ordered racemic 2D crystals.

Synthesis of structurally well-defined and liquid-phase-processable graphene nanoribbons.

The properties of graphene nanoribbons (GNRs) make them good candidates for next-generation electronic materials. Whereas 'top-down' methods, such as the lithographical patterning of graphene and the unzipping of carbon nanotubes, give mixtures of different GNRs, structurally well-defined GNRs can be made using a 'bottom-up' organic synthesis approach through solution-mediated or surface-assisted cyclodehydrogenation reactions. Specifically, non-planar polyphenylene precursors were first 'built up' from small molecules, and then 'graphitized' and 'planarized' to yield GNRs. However, fabrication of processable and longitudinally well-extended GNRs has remained a major challenge. Here we report a bottom-up solution synthesis of long (>200 nm) liquid-phase-processable GNRs with a well-defined structure and a large optical bandgap of 1.88 eV. Self-assembled monolayers of GNRs can be observed by scanning probe microscopy, and non-contact time-resolved terahertz conductivity measurements reveal excellent charge-carrier mobility within individual GNRs. Such structurally well-defined GNRs may prove useful for fundamental studies of graphene nanostructures, as well as the development of GNR-based nanoelectronics.

A tale of tails: alkyl chain directed formation of 2D porous networks reveals odd-even effects and unexpected bicomponent phase behavior.

Supramolecular self-assembly of suitably functionalized building blocks on surfaces can serve as an excellent test-bed to gain understanding and control over multicomponent self-assembly in more complex matter. Here we employ a powerful combination of scanning tunnelling microscopy (STM) and molecular modeling to uncover two-dimensional (2D) crystallization and mixing behavior of a series of alkylated building blocks based on dehydrobenzo[12]annulene, forming arrays of nanowells. Thorough STM investigation employing high-resolution spatial imaging, use of specially designed marker molecules, statistical analysis and thermal stability measurements revealed rich and complex supramolecular chemistry, highlighting the impact of odd-even effects on the phase behavior. The methodology and analysis presented in this work can be easily adapted to the self-assembly of other alkylated building blocks.

Self-assembly of an asymmetrically functionalized [6]helicene at liquid/solid interfaces.

STM brings to light chirality aspects of the self-assembly of a functionalized helicene at the interface between a liquid and the solid substrates, gold and graphite. This reveals conditions for conglomerate formation.

Structurally defined graphene nanoribbons with high lateral extension.

Oxidative cyclodehydrogenation of laterally extended polyphenylene precursor allowed bottom-up synthesis of structurally defined graphene nanoribbons (GNRs) with unprecedented width. The efficiency of the cyclodehydrogenation was validated by means of MALDI-TOF MS, FT-IR, Raman, and UV-vis absorption spectroscopies as well as investigation of a representative model system. The produced GNRs demonstrated broad absorption extended to near-infrared region with the optical band gap of as low as 1.12 eV.

Role of substrate in directing the self-assembly of multicomponent supramolecular networks at the liquid-solid interface.

The self-assembly of multicomponent networks at the liquid-solid interface between Au(111) or highly oriented pyrolytic graphite (HOPG) and organic solvents was investigated using scanning tunneling microscopy. Alkoxylated dehydrobenzo[12]annulene (DBA) derivatives form hexagonal nanoporous networks, which trap either single molecules of coronene (COR) or small clusters of COR and isophthalic acid to form multicomponent networks. The pattern of interdigitation between alkyl chains from DBA molecules produces hexagonal pores that are either chiral or achiral. On Au(111) substrates multicomponent networks display an ordered superlattice arrangement of chiral and achiral pores. In comparison, similar networks on HOPG display only chiral pores. The unique superlattice structure observed on Au(111) is related to a lower energetic preference for chiral pores than on HOPG and increased diffusion barriers for guest molecules. The increased diffusion barriers for guests allow them to act as nucleation sites for the formation of achiral pores. Following the initial nucleation of an achiral pore, restrictions imposed by the accommodation of guests within the porous network mean that subsequent growth naturally leads to the formation of the superlattice structure.