Non-Covalent Chemistry on Surface-Confined, Isolated Dendrimers

A “bottom‐up” fabrication of nanometer‐scale dendritic structures via the growth of isolated, nanosized supramolecular structures on gold surfaces is presented. A novel dendritic wedge containing peripheral pyridines and a focal dialkylsulfide chain (9) was synthesized and its coordination chemistry in solution was tested with a second‐generation Fréchet dendron functionalized with a focal SCS PdII pincer moiety (13). Replacement of the labile acetonitrile in 13 by the pyridine groups of 9 converts dendritic wedge 9 into fourth‐generation metallodendron 9 · 134 in one step. Based on these results the spatially confined growth on a gold surface was studied. The dendritic molecules with reactive pyridine groups at the periphery (9) were first spatially isolated by inserting them into decanethiol self‐assembled monolayers (SAMs) on a gold surface. Subsequently, the peripheral pyridines were reacted via metal–ligand coordinative interactions by exposing the monolayer to a solution of dendritic wedges containing focal SCS PdII pincer moieties (13). The isolated molecules inserted into the original SAM in the first step were resolved by ex‐situ tapping‐mode atomic force microscopy (TM‐AFM). The subsequent PdII–pyridine coordination resulted in a significant increase in size of the individually resolved molecules. Reference experiments demonstrated that the increased size of the isolated dendrimers on the gold substrate was a result of specific metal–ligand interactions. The methodology presented herein allows the creation of surface‐confined architectures and potentially provides a viable complement to currently employed “top‐down” methods in nanofabrication. A “bottom‐up” fabrication of nanometer‐scale metallodendrimers, embedded in self‐assembled monolayers on a gold surface, via non‐covalent growth of isolated, nanometer‐sized supramolecular structures is presented, as shown in the Figure. The size increase of the isolated dendrimers upon metal–ligand coordination was resolved by ex‐situ tapping‐mode atomic force microscopy.