Dendrimers first-generation

The reaction of the first-generation dendron 29 with the core, which is a trin-uclear platinum complex (30) bridged by 1,3,5-triethynylmesitylene, in a molar ratio of 3 1 resulted in the formation of the first-generation dendrimer (31). Since the reaction proceeded quantitatively and no side products were observed, the first-generation dendrimer was easily isolated by alumina column chromatography. 

The first-generation dendrimer 51 was directly observed by transmission electron microscopy (TEM). The TEM image showed that the dimensions of individual molecules are about 50 A, which is consistent with the calculated one [36]. Third-order NLO measurements showed a significant enhancement of two-photon absorption upon proceeding from the constituent molecules to the dendritic complex [35]. 

The [Ru(bpy)3] + core has more recently been used to construct first-generation dendrimers containing coumarin-450 chromophoric groups. 

The enzymatic polymerization of 12-hydroxydodecanoic acid in the presence of 11-methacryloylaminoundecanoic acid conveniently produced the methacrylamide-type polyester macromonomer. Lipases CA and CC were active for the macromonomer synthesis. Enzymatic selective monosubstitution of a hydroxy-functional dendrimer was demonstrated. Lipase CA-catalyzed polymerization of 8-CL in the presence of the first generation dendrimer gave the poly(8-CL)-monosubstituted dendrimer. 

Other first-generation dendrimers built around multichelating ligands are the trinuclear complexes 29 - 38 [50-52] and several hexanuclear complexes (for representative examples, see 39 and 40) [53]. In all of these compounds, the photophysical properties are equivalent to those of their building blocks. In the mixed-metal complexes 31 and 34 [50b] the Ru(II)- and Os(II)-based chromo-phores are only weakly-coupled and a dual luminescence is observed. 

First generation dendrimers (tetranuclear complexes) of the same family with branches containing different metals have also been synthesized and energy migration patterns leading to one or two peripheral units have been obtained [58]. 

Fig. 11. Enzymatic synthesis of poly( -CL) monosubstituted first generation dendrimer...

CHART 4.27 Chemical structure of a first-generation dendrimer. 

A rather novel application of the Diels-Alder reaction is the synthesis of dendrimers. Mullen and coworkers116 made cyclopentadienone 161 react with SA AA -tetraethynylbi-phenyl 162. This afforded, after extrusion of carbon monoxide, a first generation dendrimer 163 containing 22 phenyl rings (equation 45). Cyclopentadienone 161 reacted only as a diene, since the bulky triisopropyl groups prevented the ethynyl functions from reacting. 

Fig. 26 Dendrimer wedges and first-generation dendrimers that have been used as catalysts with hydrogen peroxide in thiolperoxidase- and haloperoxidase-like reactions.

Koch [82] and optimized further by us. The polyphenylene 28, which represents a first-generation dendrimer, forms 28 new bonds yielding the planar polycyclic aromatic hydrocarbon 56 (Scheme 23). Owing to its extreme insolubility in all common solvents, PAH 56 is characterized by laser desorption mass spectrometry based on its M+ peak at miz =1621. 

Attempts to isolate the ferrocenyl dendrimers described above in a crystalline form suitable for X-ray structural determination have so far been unsuccessful. For this reason, we have used computer-generated molecular models in order to gain further information about the structural features of these materials. Figure 3 illustrates an energy-minimized structure determined from CAChe molecular mechanic calculations of the ferrocenyl dendrimer 2. From these studies, we have measured approximate diameters of 2 run for the first-generation dendrimers 1,3, and 5, and 3 nm for the second-generation dendrimers 2,4, and 6. 

Fig. 1. Structures of compounds used in this investigation 1 - first generation dendrimer, 2 - second generation dendrimer, 3 - terrylendiimide-only compound, 4 - peryleneimide-only compound, 5 -first generation dendrimer with tetracarbonyl core...

Fig. 2. Normalized steady state absorption (left part) and fluoresecence spectra (right part) of first generation dendrimer (solid line) and second generation dendrimer (dotted line).

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