Polyamidoamine dendrimers have been surface-modified via peptide coupling with pyridyl, bipyridyl, and terpyridyl ligands to give the analogous polypyridyl dendrimer ligands in high yield. Complexation of the pendant chelating groups with appropriate ruthenium(II) precursor complexes yielded dendrimers surface-functionalized with tris(bipyridyl)ruthenium(II) or bis(terpyridyl)ruthenium(II) pendant complexes. Electrochemical studies of the dendrimer complexes show metal-centered and ligand-centered redox couples. These molecules also adsorb onto platinum electrodes, and the deposition process and the properties of the resulting films have been investigated with the electrochemical quartz crystal microbalance. The resulting films exhibit morphological changes with potential that can be attributed to the deposition or dissolution of the dendrimer and/or to ejection or incorporation of counterions and/or solvent into the film. A number of the electrodeposited films exhibited charge trapping peaks. Dendrimers containing terminal tris(bipyridyl)ruthenium(II) complexes exhibited room-temperature luminescence, while these and dendrimers with terminal bis(terpyridyl)ruthenium(II) complexes exhibited luminescence in a rigid butyronitrile matrix at 77 K.

The thermodynamics and kinetics of adsorption of the redox-active tris(bipyridyl)ruthenium(II) pendant poly(amido amine) (PAMAM) dendrimers and bis(terpyridyl)ruthenium(II) pendant PAMAM dendrimers (generations 0, 1, 2, 3, and 4) have been studied using electrochemical methods. All of these metallodendrimers adsorb onto Pt electrodes at +0.8 V vs Ag/AgCl where the Ru sites of the dendrimers have 2+ charges and the adsorption thermodynamics are well characterized by the Langmuir adsorption isotherm. The kinetics of adsorption were found to be activation controlled with the rate constant decreasing with decreasing dendrimer generation. Electrochemically determined coverages were significantly larger than calculated values determined from the dimensions of the metallodenrimers obtained from molecular modeling. These comparisons suggest that upon adsorption, the dendrimers appear to compress to dimensions significantly smaller than those calculated.

The interfacial reaction of the terpyridyl-pendant dendrimers (dend-n-tpy; n ) 4, 8, 32) and of the bridging ligand 1,4-bis[4,4′′-bis(1,1-dimethylethyl)-2,2′:6′,2′′terpyridine-4′-yl]benzene (BBDTB) dissolved in CH2Cl2 with aqueous Fe 2+ or Co 2+ gives rise to film formation on highly oriented pyrolytic graphite surfaces. Molecularly resolved scanning tunneling microscopy (STM) images reveal that these films form highly ordered 2-D hexagonal arrays which appear to be composed of one-dimensional polymeric strands with a repeat unit of (tpy-dend-tpy-M)x in the case of dendrimers or (tpy-bridge-tpy-M)x in the case of BBDTB (M ) Fe 2+ , Co 2+ ). The extension of the ordered domains appears to be delimited by terrace width. The dimensions obtained from an analysis of STM images is consistent with the size of the dendrimer or the bridging ligand (obtained from molecular modeling) from which the films are derived. In the case of films derived from dend-n-tpy the ordering is dependent on the dendrimer generation. In all cases, the films are electrochemically active and exhibit a reversible wave at a formal potential that corresponds to the respective [M(tpy)2] 2+ complex.

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