Redox-active dendrimers metal complexes

Our aim has been the construction of dendrimers that incorporate in their building blocks specific pieces of information such as the capability to absorb and emit visible light and to reversibly exchange electrons.To pursue this aim, we have designed a synthetic strategy to build up dendrimers based on luminescent and redox-active transition metal complexes. Species containing 4, 6, iP 10,2W7 28 gjjj 222930 metal-based units have already been obtained. We will see... 

Campagna S, Denti G, Serroni S, Juris A, Venturi M, Ricevuto V, Balzani V (1995) Dendrimers of nanometer size based on metal complexes Inminescent and redox-active polynuclear metal complexes containing np to twenty-two metal centers. Chem Eur J 1 211-221... 

Serroni S, Juris A, Venturi M, Campagna S, Resino IR, Denti G, Credi A, Balzani V (1997) Polynuclear metal complexes of nanometre size. A versatile synthetic strategy leading to luminescent and redox-active dendrimers made of an osmium(II)-based core and ruthenium (Il)-based units in the branches. J Mater Chem 7 1227-1236... 

PBE dendrons bearing a focal bipyridine moiety have been demonstrated to coordinate to Ru + cations, exhibiting luminescence from the metal cation core by the excitation of the dendron subunits [28-30]. The terminal peripheral unit was examined (e.g., phenyl, naphthyl, 4-f-butylphenyl) to control the luminescence. The Ru +-cored dendrimer complexes are thought to be photo/redox-active, and photophysical properties, electrochemical behavior, and excited-state electron-transfer reactions are reported. 

In order to build up dendrimers crqrable of exhibiting redox activity and light-induced functions, appropriate building blocks have to be used. In the last 20 years, extensive investigations carried out on the photochemical and electrochemical properties of transition metal compounds have shown that Ru(II) and Os(ll) complexes of aromatic M-heterocycles (Figure 1), e.g., Ru(bpy)j and Os(bpy)j (bpy = 2,2 -bipyridine), exhibit a unique combination of chemical stability, redox properties, excited state reactivity, luminescence, and excited state lifetime. Furthermore all these properties can be tuned within rather broad ranges by... 

For the formation of metallodendrimers of precise nature, a second favorable position in the overall structure for complexation can obviously be at the periphery. Excellent examples of such systems have been reported that include a silicon dendrimer decorated with 243 ferrocenyl units at the periphery with stable redox activity [58]. Catalytic activity of dendrimers with metals located at the periphery has also proven to be of great interest as it has been recently reviewed by several authors [59,60]. Placing photoactive centers at this specific location can nonetheless be more intricate in this case, as demonstrated by the limited number of reported examples. 

There has been considerable investigation of dendritic species with redox-active moieties placed at the center of the molecule. Various metal-polypyridyl complexes, as well as porphyrins and phthalocyanines, have been used as cores around which dendrimers have been built. Dendritic molecules with metallocenes at or near the core and dendrimers with central metal clusters have also been synthesized. In addition to metal complexes, electroactive organic moieties have been placed at the cores of various types of dendrimers. The rate of electron transfer between redox-active species and a working electrode, and... 

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