Redox-active core dendrimers

BACK TO SOLUTION AGAIN HOMOGENEOUS ELECTRON TRANSFER BETWEEN REDOX-ACTIVE CORE DENDRIMERS... 

Cameron CS, Gorman CB (2002) Effects of site encapsulation on electrochemical behavior of redox-active core dendrimers. AdvFunct Mater 12 17-20... 

Gorman, C.B., Dendritic encapsulation as probed in redox active core dendrimers Comptes Rendus Chimie. 2003, 6, 911-918... 

Cameron, C.S. Gorman, C.B. Effects of Site Encapsulation on electrochemical behavior of redox-active core Dendrimers. Adv. Funct. Mater. 2002. 12, 17. 

Gorman CB, Smith JC, Hager MW, Parkhurst BL, Sierzputowska-Giaez H, Haney CA (1999) Molecular structure-property relationships for electron-transfer rale attenuation in redox-active core dendrimers. J Am Chem Soe 121(43) 9958-9966... 

A tetrathienylenevinylene core was used to obtain the dendrimers 82-84 (generations 1-3, respectively) [154]. Oxidation in CH2CI2 of the electroactive core occurs in two reversible monoelectronic processes, with identical cyclovoltammetric waves for compounds 82 84. The absence of any effect of the dendrimer generation indicates that the electroactive core is not encapsulated in the dendritic structure, as is commonly observed. The authors suggest that in this case the redox-active core is too long to be completely surrounded by the dendritic branches. 

Another advantage of dendrimer-based catalysts concerns their easy recovery by stabilization at the surface of a polymer. The principal activities in dendritic catalysis lie in homogeneous catalysis, including Kharash addition of CC14 to methacrylate, palladium-catalyzed allylic alkylation, hydrogenation of olefins, hydroformylation, cyclopropanation, and oxidation.258 Dendrimers with redox-active cores have been proposed as promising materials for miniaturized information-storage circuits.259... 

As with chromophores, the steric encapsulation of a dendrimer core can be utilized to prevent intermolecular interactions between redox active sites. A number of different redox active core moieties have been investigated, including, iron—sulfide clusters,9394 bis(terpyridine)iron(II) complexes,92 tris-(bipyridine)ruthenium(II) complexes,330 zinc porphyrins,252 oligothienylenevinylenes,331 fullerenes,236,332 ferrocenes,333-336 oligothiophenes,322 oligonaphtha-lenes,337 and 4,4 -bipyridinium.338... 

Fig. 4 Examples of three different of redox-active dendrimers (a) redox-active core, (b) electrochemically active branching units, and (c) redox-active peripheral groups.

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. 

A wide range of dendrimers with functional core is described in the literature. Thus chromophores [7], electrochemically active, redox active [8], and catalyti-cally active [9] or also self-associating and chiral units as well as polymerisable monomers and polymers have been successfully introduced into the centre of dendrimers. However, the core unit not only has a determining effect on the function, but also has a decisive influence on the multiplicity, size, and shape of the dendrimer. 

An important field where the cyclopropanation reaction finds growing application is the construction of dendrimers possessing fullerenes either as functional cores [26-33] or branches [34-38]. Dendrimers can serve as building blocks for the construction of organized materials with nanosize precision due to the well-defined three-dimensional structure they possess. An issue of great importance is to incorporate photoactive and/or redox-active units at the center of the dendrimer in order to establish these types of materials as molecular devices. An example of an organofullerene material that has the potential to serve as a core building block for the construction of dendrimeric compounds... 

Examination of the cyclic voltammetry (CV) of the Zn-porphyrin dendrimers in THF and CH2C12 with Bu4N+PF6 (0.1 m) electrolyte revealed first oxidation potentials up to 300 mV (THF) less positive than the corresponding values obtained for the unshielded tetraester, Zn-porphyrin core. These preliminary electrochemical experiments suggested dendritic encapsulation of redox-active chromophores can effectively influence the electrophone environment controlled and well-conceived cascade architecture can lead to new avenues of selective redox catalyst design. 

S. Nlate, J. Ruiz, V. Sartor, R. Navarro, J.-C. Blais, and D. Astruc, Molecular Batteries Ferrocenylsilylation of Dendrons, Dendritic Cores, and Dendrimers New Convergent and Divergent Routes to Ferrocenyl Dendrimers with Stable Redox Activity, Chem. Eur. J. 6, 2544-2553 (2000). 

---