Electrochemical and Guest Binding Properties of Fréchet- and Newkome-Type Dendrimers with a Single Viologen Unit Located at Their Apical Positions
详细信息 查看全文
- 作者：Winston Ong ; Jodi Grindstaff ; David Sobransingh ; Rosa Toba ; José ; Marí ; a Quintela ; Carlos Peinador ; and Angel E. Kaifer
- 刊名：Journal of the American Chemical Society
- 出版年：2005
- 出版时间：March 16, 2005
- 年：2005
- 卷：127
- 期：10
- 页码：3353 - 3361
- 全文大小：176K
- 年卷期：v.127,no.10(March 16, 2005)
- ISSN：1520-5126
文摘
Several new series of dendrimers containing a single redox-active 4,4'-bipyridinium (viologen)residue were synthesized and characterized. In these dendrimers, the viologen group is covalently attachedto the apical position of a Newkome- or Fréchet-type dendron, ranging in size from first to third generationof growth. The half-wave potentials corresponding to the two consecutive one-electron reductions of theviologen residue are affected by the size of the dendritic component. The size effects are more pronouncedin the Newkome-type dendrimers and seem to result from the polarity contrast between the microenvironments provided by the solution and the internal phase of the dendrimer. Unlike in many other dendrimershaving a redox-active core, the voltammetric behavior remains fast (reversible) even in third generationdendrimers. Pulse gradient stimulated echo NMR diffusion coefficient measurements on the Newkome-type dendrimers reveal that their hydrodynamic radii are relatively invariant in solvents of widely differentpolarities (dichloromethane to dimethyl sulfoxide). The host-guest binding interactions between the viologenresidue in these dendrimers and the crown ether host bis-p-phenylene-34-crown-8 were also investigated.While in Newkome-type dendrimers the growth of the dendron caused a substantial attenuation of thebinding constant values, this size effect was not observed in the Fréchet-type dendrimers. Theseelectrochemical and binding measurements underscore some of the structural differences between thesetwo common types of dendritic architectures.