Photophysics of PANAM-based dendrimers of polypyridyl complexes of ruthenium

The photophysics of PAMAM (poly-amidoamine) based dendrimers (generations G0-G4) modified with (4, 8, 16, 32, and 64) pendant- [Ru(tpy)(2)](+2) (tpy is 2,2':6',2"-terpyridine) and [Ru(bpy)(3)](+2) (bpy is 2,2'-bipyridine) chromophores have been studied in both fluid solution at 298 K and frozen glasses, at 77 K. The absorption and emission spectra, the excited-state lifetimes and quantum yields have been obtained for both families of metallodendrimers. In general and in analogy to the behavior exhibited by the discrete molecules (i.e., [Ru(tpy)(2)](+2) and [Ru(bpy)(3)](+2)), the bipyridine derivatives exhibit longer lifetimes and higher quantum yields when compared to the corresponding terpyridine complexes. Some generation dependent changes have also been observed. We have also explored the effects of solvent by comparing results in butyronitrile and dimethylacetamide with the latter being used as a mimic of the dendritic backbone. Our results suggest that for the higher generations the dendritic backbone acts as the solvent in affecting the photophysical behavior.