Synthesis with Single Macromolecules: Covalent Connection between a Neutral Dendronized Polymer and Polyelectrolyte Chains as well as Graphene Edges.

Single chains of a neutral, dendronized polymer with peripheral azide groups (PG3A) are co-deposited onto molecularly modified graphite substrates with a positively charged dendronized polymer (PG2) as well as with negatively charged plasmid dsDNA. PG3A is also prepared near graphite step-edges. Single PG3A chains are moved with a scanning force microscope tip, into close contact with either of the two polyelectrolytes, as well as the step-edge at predetermined positions. Treating these structures in situ with UV light leads to photochemically induced cross-linking between the PG3A chains carrying azide groups and PG2, dsDNA, and graphite step-edges, respectively, which is proven by mechanically challenging the "welding" points by pulling on the molecules with the SFM-tip.

Covalent connection of individualized, neutral, dendronized polymers on a solid substrate using a scanning force microscope.

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.