Micrometre-long covalent organic fibres by photoinitiated chain-growth radical polymerization on an alkali-halide surface

On-surface polymerization is a promising technique to prepare organic functional nanomaterials that are challenging to synthesize in solution, but it is typically used on metal substrates, which play a catalytic role. Previous examples on insulating surfaces have involved intermediate self-assembled structures, which face high barriers to diffusion, or annealing to higher temperatures, which generally causes rapid dewetting and desorption of the monomers. Here we report the photoinitiated radical polymerization, initiated from a two-dimensional gas phase, of a dimaleimide monomer on an insulating KCl surface. Polymer fibres up to 1 μm long are formed through chain-like rather than step-like growth. Interactions between potassium cations and the dimaleimide’s oxygen atoms facilitate the propagation of the polymer fibres along a preferred axis of the substrate over long distances. Density functional theory calculations, non-contact atomic force microscopy imaging and manipulations at room temperature were used to explore the initiation and propagation processes, as well as the structure and stability of the resulting one-dimensional polymer fibres

On-Surface Polymerization: From Polyarylenes to Graphene Nanoribbons and Two-Dimensional Networks

On-surface polymerization is a novel technique for the fabrication of one- and two-dimensional molecular networks confined on a surface and is a rapidly developing field in surface science. The molecular building blocks exhibit pre-defined connection sites at which, after thermal activation and diffusion on the surface, the molecules are linked in a clean environment. Depending on the position and number of these connection sites, activated molecules polymerize to yield chains or two-dimensional networks. The chemical composition of the resulting polymer is precisely defined by the precursor molecules. We review current developments in the field of on-surface polymerization and present different examples, including the fabrication of graphene nanoribbons. We introduce reductive Ullmann-type coupling as well as Scholl-type cyclodehydrogenation for fabrication of graphene nanoribbons of increasing width. The surface plays a crucial role during the activation and polymerization processes because it serves as a catalyst, promotes molecular diffusion, and has a huge influence on the final molecular architecture. One-dimensional polymers can act as molecular wires and their conductance has been studied at the level of individual chains. In addition, we discuss two-dimensional networks and describe recent progress in attempts to improve their quality using sequential activation or defect-healing

Molecular trapping in two-dimensional chiral organic Kagomé nanoarchitectures composed of Baravelle spiral triangle enantiomers

International audienceThe supramolecular self-assembly of a push-pull dye is investigated using scanning tunneling microscopy (STM) at the liquid-solid interface. The molecule has an indandione head, a bithiophene backbone and a triphenylamine-bithiophene moiety functionalized with two carboxylic acid groups as a tail. The STM images show that the molecules adopt an "L" shape on the surface and form chiral Baravelle spiral triangular trimers at low solution concentrations. The assembly of these triangular chiral trimers on the graphite surface results in the formation of two types of chiral Kagomé nanoarchitectures. The Kagomé-α structure is composed of only one trimer enantiomer, whereas the Kagomé-β structure results from the arrangement of two trimer enantiomers in a 1:1 ratio. These Kagomé lattices are stabilized by intermolecular O-H···O hydrogen bonds between carboxylic acid groups. These observations reveal that the complex structure of the push-pull dye molecule leads to the formation of sophisticated two-dimensional chiral Kagomé nanoarchitectures. The subsequent deposition of coronene molecules leads to the disappearance of the Kagomé-β structure, whereas the Kagomé-α structure acts as the host template to trap the coronene molecules