Covalent Connection of Individualized, Neutral, Dendronized Polymers on a Solid Substrate Using a Scanning Force Microscope

Abstract

The synthesis of a neutral, high-molar-mass, acrylamide-based, third-generation dendronized polymer (denpol) with a defined number of azide groups at its periphery is reported. An attach-to route is used in which a first-generation denpol is reacted with second-generation (G2) dendrons. The degree of structure perfection of the resulting denpol is quantified as 99.8 %. This value was obtained after the introduction of a fluorescence label at the sites that remained unaffected by the dendronization. The high coverage was independently confirmed for the dendronization of another first-generation polymer and a closely related G2 dendron. The third-generation denpol resulting from the first dendronization experiment was spin-coated as a sub-monolayer onto highly oriented graphite precoated with an ultrathin layer of C12H25NH2, which was introduced to provide a well-defined substrate for denpol adsorption and manipulation. Scanning force microscopy revealed single denpols, which could be moved across the surface and "welded" by covalent cross-linking induced by photochemical decomposition of the azides into highly reactive nitrenes. The successful formation of covalent bonds between two denpols was confirmed by mechanically challenging the link with the scanning force microscope (SFM) tip. This is the second reported case of a move-connect-prove sequence using polymers and the SFM, which for the first time employs noncharged denpols, thus widening the applicability of this method significantly.

Scanning Force Microscopy as Applied to Conformational Studies in Macromolecular Research

“…[206] In some cases the dynamic transformations may be induced purposefully by direct influence of the microscope tip. [207][208][209] We have recently developed a new concept to induce macromolecular dynamics to be observed with SFM in real time regime by an exposure of adsorbed polymer chains to vapours of different nature. This concept was demonstrated in our ten papers to be discussed below.…”

Self‐Folding of Charged Single Dendronized Polymers

“…When the surface temperature decreases to room temperature after annealing, all the alkyl chains in monolayer and denpol molecules adsorbed by alkyl amine chains will solidify on the HOPG surface. [33,34] Finally, what we observed under SFM is possibly the combination of the results of decomplexation, relaxation, and solidification. Isolated polymer chains can be manipulated on a mobile surface using an SFM tip in contact mode.…”

“…Negatively charged denpols can be immobilized on a positively charged surface due to strong electrostatic interaction. [33] If the surface consists of a protonated octadecylamine monolayer a strong surface potential ripple is produced, which prevents absorbed polyelectrolyte molecules from lateral diffusion. [34] However, the question arises whether the annealing temperature, which is well above the melting point of octadecylamine on a monolayer (52 8C, as in bulk), could induce the polymer molecules to diffuse and form aggregates.…”

Molecular Workbench for Imaging and Manipulation of Single Macromolecules and Their Complexes with the Scanning Force Microscope

“…For their control, we have developed a molecular workbench consisting of an atomically flat, inert solid substrate such as the basal plane of highly oriented pyrolytic graphite (HOPG), coated with a layer of molecules such as alkanes or alkyl chains containing amphiphiles. Beyond imaging, the capability to manipulate macromolecules with the SFM provides a fundamentally new dimension for the determination of both the structure and properties of single macromolecules [25][26][27][28][29][30][31]. The key is that it allows the preparation of well-defined nonequilibrium conformations.…”