Synthesis, Characterization, Electrochemistry, and EQCM Studies of Polyamidoamine Dendrimers Surface-Functionalized with Polypyridyl Metal Complexes

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.