Dendrimers peripherally modified with a anion radicals that form pi-dimers and pi-stacks

Poly(amidoamine) (PAMAM) dendrimers, generations 1-6, were peripherally modified with cationically substituted naphthalene diimide groups. Several monomeric diimides were also prepared as models. The structure and loading of the dendrimers were determined by vis, IR, and NMR spectroscopies, elemental analysis, and coulometric analysis. In general it was possible to obtain loadings greater than 70% even from generation 6 dendrimer where there are 192 amine groups to be substituted. These polymers and monomers were reduced using sodium dithionite or electrochemically with one electron per imide group converting each imide into its anion radical. Near-infrared(NIR) spectroscopy showed that in D2O or formamide solutions the anion radicals aggregated into pi-dimers and pi-stacks. Cyclic voltammograms are interpreted in terms of anion radical aggregation and precipitation of the reduced dendrimers. The CV and NIR results for the various dendrimer generations were quite similar. These results allow insight into the possibilities and limitations of dendrimers to provide a scaffold for intramolecular aggregation.