Electronic conducting dendrimers

Near-infrared (NIR) absorption spectroscopy has been used to characterize the delocalized re-stacks on electronic conducting dendrimers by Miller and coworkers [47-49]. These dendrimers were prepared by peripherally modifying PAMAM dendrimers with cationically substituted naphthalene diimides, and then reduced with one electron per imide group to convert each imide into its anion radical. The re-stacking of these radical anions on these dendrimer surfaces was indicated by an absorbance band beyond 2000 nm in the NIR spectra. 

This work was supported in part by the MRSEC Program of the National Science Foundation under Award Number DMR-98-09687 and by NSF grant CHE98-12676 to the authors at Columbia University. 

Sayed-Sweet, Y., Hedstrand, D. M., Spindler, R. and Tomalia, D. A. J. Mater. Chem., 

Devadoss, C., Bharathi, P. and Moore, J. S. Angew. Chem. Int. Edit. Engl., 36, 1633 

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Parallel studies on PAMAM dendrimers, the Frechet type polyether den-drons, and other dendrimer families have generated an extensive list of unique properties driven by the dendritic state/ Figure 1.18 compares several significant physical property differences between the linear and dendritic topologies related to conformations, crystallinity, solubilities, intrinsic viscosities, entanglement, diffusion/mobility and electronic conductivity. 

In particular, poly(amidoamine) dendrimers were peripherally modified with diimide moieties (see the structure shown in Scheme 1.43). After rednction with dithionite, this dendrimer was cast into a film, the electronic properties of which were isotropic. (This means that on the molecular and macroscopic levels, there is a three-dimensional (3-D) electron delocalization.) The conductivity was humidity dependent. Water molecules integrate into the material s crystal structure and take part in long-distance electron transfer. Such an effect of water was also observed to enhance electric... 

Because NDIs are a popular choice of acceptor in electron transfer studies, the NDI redox and photophysical properties are well documented and, more importantly, absorbance and fluorescence maxima are known for both the neutral and radical anion species. This has led the group of Miller [25] to exploit their properties in forming conducting wires based on the doping of water-soluble NDIs by peripheral modification on the polyamidoamine (PAMAM) dendrimers 19 (Figure 11.9). 

The photocurrent generation in the present system is initiated by photoinduced charge separation from the porphyrin excited singlet state (1H2P /H2P+ = -0.7 V vs. NHE) [78] in the dendrimer to C60 (C60/Cf>0 = -0.2 V vs. NHE) [78] in the porphyrin dendrimer-C60 complex rather than direct electron injection to conduction band of Sn02 (0 V vs. NHE) system [91] The reduced C60 injects electrons into the Sn02 nanocrystallites, whereas the oxidized porphyrin (H2P/H2P+ = 1.2 V vs. NHE) [78] undergoes electron-transfer reduction with iodide (I3 /I = 0.5 V vs. NHE) [78] in the electrolyte system [91]. 

The development of amphiphilic and aggregation behaviour as a fiinction of dendrimer generation of PS-t/enstudied with several diflferent techniques the amphiphilic character at a toluene-water interface was investigated with conductivity measurements, and at a water-air interface with monolayer experiments. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) were used to examine the aggregates formed by the different generations in aqueous solutions, while the critical association concentrations were determined with the pyrene-probe luminescence technique. 

J.M. Andre and B. Champagne, in J.L. Bredas (Ed.), Nonlinear optical hyperpolarizabilities and electronic properties of oligomers and polymers the polyene story, from dyes to conducting and NLO systems, Conjugated oligomers, polymers, and dendrimers From polyacetylene to DNA, Bibliotheque Scientifique Francqui, De Boeck Universite, 1999, pp. 349-394. 

Both Buchwald and Hartwig have explored the use of palladium-catalyzed amination for the synthesis of dendrimers and polyanilines. Dendrimers, such as 48, can be easily assembled through sequential aiylation of aminoanilines.89 These dendrimers are useful in creating metal-organic frameworks and often can exhibit interesting electronic effects, such as diradicals, and as optical materials. Polymeric anilines 49 are of intense interest due to their unique electrical conducting properties. Using the... 

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