New metallodendrimers containing an octakis(diphenylphosphino)-functionalized silsesquioxane core and ruthenium(II)-based chromophores

A new class of surface-modified dendrimers has been prepared by reactions o f 8 equiv of the terpyridine-functionalized polyether monodendrons with a p olyhedral oligomeric silsesquioxane (POSS) core. Subsequent reactions of th ese spherically shaped organic dendrimers with Ru(II)-based precursors affo rd photo- and redox-active metallodendrimers. These new dendrimers have bee n characterized using a combination of mass spectral analysis (MALDI-TOF/MS , ESI/MS, and FAB/MS), nuclear magnetic resonance (H-1, C-13, Si-29, and (3 1)p{H-1} NMR), photophysical analyses (electronic absorption, emission, exc ited-state lifetime, and quantum yield) and electrochemical measurement (cy clic voltammetry). Specifically, (31)p{H-1} NMR is used to monitor the comp letion of reactions and the purity of dendrimers and metallodendrimers. The se new metallodendrimers exhibit large extinction coefficients that coincid e with the number of peripheral Ru(II)-based chromophores. With the use of (-CH2-Ph-tpy)Ru-II(bpy)(2) type of chromophores, all metallodendrimers are found emissive at room temperature, with lifetimes in the range of 605-890 ns. Photophysical data also indicate similar steady-state emission maxima a nd single-exponential decay kinetics for all metallodendrimers, and the obs erved overall quantum yields of the G1, G2, and G3 metallodendrimers are fo und to be 14, 20, and 7 times higher than that of the monomeric model compl ex (CH3-Ph-tpy)Ru(bpy)(2)(PF6)(2). Electrochemical studies reveal the prese nce of surface-confined species, in addition to the ligand-centered and met al-centered redox processes.