Porphyrin-core dendrimer

That dendrimers are unique when compared with other architectures is confirmed by an investigation on porphyrin core dendrimers and their isomeric linear analogues [63]. The isomers displayed dramatically different hydrodynamic properties, crystallinity, and solubility characteristics when compared to those of their dendritic analogues, and photophysical studies showed that energy transfer from the poly(benzylether) backbone to the core was more efficient in the dendrimer because of the shorter distance between the donor units and the acceptor core. 

Most recently, Yamamoto et al. prepared a series of porphyrin core dendrimers of the form Core 18—Rpt 12-Periph15.126 Using a Nicholson analysis of the CV data, they calculated a decrease in the value of k° from 2.6 x 10 2cm/s to 5.9 x 10 4cm/s as n increased from 1 to 4. The oxidation potential decreased across this series from 340 to 260 mV (versus Fc/Fc+ in CHCI3 CH3CN, GCE) and from 400 to 340 mV (versus Fc/Fc+ in THF, GCE). In this case, easier oxidation with increasing generation presumably reflects better stabilization of the oxidized state by the dendrimer than the solvent. This behavior is the opposite of that observed in more hydrophobic dendrimers (cf. Section 4.2). 

The iterative route to these porphyrin-core dendrimers employed the readily available ethereal building block 163.11911 Thus, amine acylation (DCC, 1-HBT, THF) of monomer 163 (Scheme 4.46) with tetraacid 166 afforded the first tier dodecaester 167a, which upon termini transformation (LiOH, Me0H/H20 (1 1)) of the polyester gave the polyacid 167b. Repetition of this sequence allowed the construction of two additional tiers, e.g., ester 168. 

Photoinduced electron transfer quenching of a porphyrin-cored dendrimer was first reported in compound 52, where the fluorescence of the Zn core is quenched in acetonitrile by vitamin K3 (2-methyl-1,4-naphtoquinone) [123]. 

Onitsuka and Takahashi reported the synthesis and characterization of zinc porphyrin core dendrimers with platinum acetylide based dendrons... 

Scheme 25 Porphyrin core dendrimers with platinum acetylide dendrons by Onitsuka and coworkers [76]...

Scheme 27 Porphyrin core dendrimers with carbazole dendrons by Dehaen [78] (top) and Lu [79] (bottom)... 

Scheme 40 Porphyrin core dendrimers with TPA donors for singlet oxygen sensitization by Fr chet and Prasad [109,110]...

In order to explore the influence of glycodendrimer branches on the photophysical properties of photoactive cores, Stoddart at al. presented two carbohydrate shells, in their protected 267b and deprotected 267a forms, containing a porphyrin core. Dendrimer 267b was prepared in 16% yield from /3-D-glucopyranose building block 266 [173] and meso-tetrafunctionalized por-... 

Figure 15 Schematic representation of porphyrin-cored dendrimer which bears 16 coumarin nnits in the outer layer and 8 naphthopyranone units in the inner layer. ...

Other examples have been reported by Aida et al. [269], wherein they reported an electrostatically, directed assembly of porphyrin core dendrimers to produce large infinite aggregates as illustrated below (Figure 43). Energy transfer constants were obtained and used to determine distances between acceptors and donors as demonstrated that communication occurred between those domains. 

Frechet and coworkers synthesized porphyrin cored dendrimers (Figure 12) and their architecturally isomeric linear analogues which were... 

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