Functional units in the dendrimer scaffold

In the synthesis of functional dendrimers, interest has hitherto been focussed on variation of the functional core unit or peripheral groups and the resulting effects on the properties of the dendrimer. For a long time, the only function ascribed to the dendritic branches and their repeating units was that of a scaffold linking periphery and core. It was overlooked that, in the interior of the dendrimer scaffold, an individual characteristic (nano)environment can arise which is largely dependent upon the chemical characteristics and the polarity of the repeating units used to construct the dendrimer. Moreover, they can facilitate cascade processes and serve as a platform for cooperative effects between dendrimer branches [37]. 

Y Monomeric branching unit 0,1 Various functional groups 

Schliiter et al. successfully accomplished generation-specific incorporation of an individual aryl bromide functionality into poly(benzyl ether) dendrimers. Whatever its position in the dendrimer framework, this bromide function could also be utilised for further chemical modification because it can react with aryl-boronic acid via Suzuki cross-coupling [42]. 

Subsequent modification of the branching units in the interior of a dendrimer framework has so far received comparatively tittle attention. From a synthetic standpoint, however, this strategy offers significantly more design scope than its counterpart. Thus dendrimers also become accessible whose branching units are hard to synthesise or are either not sufficiently reactive or too sensitive to be used in iterative dendrimer synthesis. However, restricted accessibility of internal groups compared to peripheral functionalities can prove problematic. 

The literature contains mainly references to subsequent internal functionalisation of Frechet dendrimers [44]. The suitability of this type of dendrimer comes 

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Whereas the bifunctionalisation strategies presented so far are relatively straightforward, the synthesis of multifunctional dendrimers with more than two kinds of functional units requires considerable synthetic effort. Preparation of dendrimers with a functional core and additional functional units in the dendrimer scaffold and in the periphery requires de novo synthesis of the entire dendrimer scaffold, with the synthesis conditions having to be tolerable for all groups (Fig. 3.15). 

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