Silver dendrimers

The broad emission band displayed by these silver/dendrimer constructs actually was found to consist of 5 overlapping fluorescent peaks caused by individual silver/dendrimer complexes. Each of these complexes evidently contained a uniquely sized silver nanocluster, which resulted in an individual emission peak. Therefore, all the silver/dendrimer complexes together in solution presented a combined average of these 5 discrete emission peaks, and thus displayed the broad emission band covering nearly 200 nm in width across the spectrum. 

The remaining sections outline recent findings on the optical properties of metal-dendrimer nano-composites. The sections have been organized into areas of interest related to the fabrication as well as photophysical properties of these new and important materials. The first section discusses some of the important issues concerning the fabrication of these novel materials and their chemical characterization. The second section discusses the linear and nonlinear optical properties of these materials. The third section provides details related to the ultrafast emission properties of gold- and silver-dendrimer nanocomposites. 

Figure 21.3 Nonlinear transmission of silver -dendrimer nanocomposites Ag(0) E at 532 nm. Pulse repetition rate- 10 Hz. Inset nonlinear transmission results for Ag(0) E in a concentration of 2.95x 10 4 mole/kg at 532 nm, with the variation of the pulse repetition rate t indicates the specific repetition periods.

Lesniak W, Bielinska AU, Sun K, Janczak KW, Shi X, Baker JR, Balogh LP (2005) Silver/ dendrimer nanocomposites as biomarkers fabrication, characterization, in vitro toxicity, and intracellular detection. Nano Lett 5 2123-2130... 

Let us now examine the case of a nonlinear scattering process. Ispasoiu et al. deduced from considerations regarding the excited-state lifetime that the optical limiting observed using nanosecond laser pulses at X = 532 nm in their silver-dendrimer nanocomposite aqueous solution was due to absorption-induced nonlinear scattering [142]. They suggested that the scattering centres were micro-bubbles... 

Lesniak et al. (2005) also describe the preparation and use of similar dendrimer/silver nanoclusters using G-5 PAMAM dendrimers terminated with either amino, hydroxyl, or... 

Zheng, J., and Dickson, R.M. (2002) Individual water-soluble dendrimer-encapsulated silver nanodot fluorescence./. Am. Chem. Soc. 124, 13982-13983. 

Dendrimer synthesis, 26 787-788 breakthrough approaches in, 26 788 Dendritic box, 26 790 Dendritic metallic silver, 19 367—368 Dendritic nanoparticles, water-soluble, 26 796... 

Ultrafast emission measurements are possible with the dendrimer metal nanocomposites. The gold and silver internal dendrimer nanocomposites showed a fast emission decay of approximately 0.5 ps, which was followed by a slower decay process. The fast decay emission is attributed to decay processes of the gold (or silver) metal nanoparticles. Ultrafast emission anisotropy measure-... 

In general, silver clusters in solution are prepared by reduction of silver ions. Proper scaffolds, e.g., DNA, proteins, dendrimers and polymers, are essential to prevent the aggregation of clusters to larger nanoparticles. Although it is clear that the emission originates from few-atom silver clusters, many aspects of this exciting class of nanoscopic metals are not yet fully understood. 

Since it is anticipated that Ag+ ions strongly adsorb on the dendrimers with surface carboxyl groups through electrostatic attractive forces, synthesis of den-drimer-silver nanoparticles is carried out by the reduction of AgN03 with sodium borohydride in the presence of dendrimers with surface carboxyl groups (G(3.5-5.5)). When Ag+ ions are reduced with sodium borohydride in the presence of dendrimers, the color of silver particles changes with an increase of G5.5 concentration yellow at the ratio of [carboxyl group]/[Ag+]=1 turns to or-... 

Fig. 9. Absorption spectra of silver nanoparticles synthesized in the presence of dendrimer. Reprinted with permission from [21]. Copyright 2002 American Chemical Society...

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