Dendrimers porphyrin assemblies

Scheme 3 Schematic representations of electrostatic assemblies of dendrimer porphyrins 6a, 7a with MV2+...

N. Tomioka, D. Takasu, T. Takahashi, T. Aida, Electrostatic Assembly of Dendrimer Electrolytes Negatively and Positively Charged Dendrimer Porphyrins , Angew. Chem. Int. Ed., 37,1531 (1998)... 

Tomioka N, Takasu D, Takahashi T, Aida T (1998) Electrostatic assembly of dendrimer electrolytes negatively and positively charged dendrimer porphyrins. Angew Chem Int Ed 37 1531-1534... 

Other supramolecular structures such as dendrimers have also been synthesized with zinc-containing porphyrins. Sixteen free base and sixteen zinc porphyrin units were added at the fifth generation of dendritic poly(L-lysine) and intramolecular fluorescence energy transfer was observed.823 Assembly of supramolecular arrays in the solid state has been achieved with the incorporation of an amide group for hydrogen bonding. Zinc meso-tetra(4-amidophenyl)porphyrin... 

Figure 16.17 Amine-terminated polypropylene imine) dendrimers act as tridentate ligands for the complexation of transition metals [217] (a), and can function as templates for the assembly of Troger s base dizinc(ll) bis-porphyrin molecules, (b) [218]...

Fluorescence lifetime measurements on the aggregate have shown that the rate constant of the intermolecular energy transfer from the zinc porphyrin unit to the free-base porphyrin unit has been evaluated to be 3.0 x 109 s-1. This value is reasonable from a model in which dendritic donor 6b and acceptor 5a contact each other directly at their exterior surfaces (Scheme 2). Therefore, electrostatic assembly of positively and negatively charged dendrimers provides a promising supramolecular approach to construct photofunctional materials with nanometric precision. 

Long-range electron transfer reactions have attracted attention relative to the initial stages of photosynthesis, and special interest has been focused on the design of noncovalently assembled donor-acceptor arrays. Dendrimers with spatially isolated porphyrin cores are potential motifs for investigating such long-range electron transfer reactions [12],... 

Porphyrin-based self-assembled molecular squares 389 can form mesoporous thin films in which the edge of a square, thus the size of the cavity, can be adjusted by appropriate choice of substituents [8]. Fibers that form coil-coiled aggregates with distinct, tunable helicity are built from crown ethers bearing porphyrins 390 [9]. In addition to the porphyrin applications discussed in Sections 6.3.2.2 and 6.4, dendrimer metalloporphyrins 391 to be applied in catalysis [10] and the water-soluble dendritic iron porphyrin 319 modelling globular heme proteins [11] can be mentioned. 

Fig. 13.23 Porphyrin dendrimers and the reference compound employed for construction of organic solar cells composed of multi-porphyrin/C60 supramolecular assemblies [91].

The periphery of convergently synthesized den-drimers has also been modified to allow the assembly of monolayers,494 to support dendritic catalysts,495 to control the intermolecular assembly of porphyrin dendrimers,246 to probe the effect of photo isomerization,319 and to enable cross-linking of the periphery followed by removal of the core.496 These studies in peripheral modification highlight the versatility of the convergent synthesis. In particular, the ability to selectively modify the periphery and focal functionalities of a dendron enables the design of complex macromolecules that involve the interaction between multiple functional components. 

Figure 5.14 Schematic diagram for the self-assembly of tin(IV) porphyrin-containing dendrimer into nanotubes. (From Kim et al.73)...

The bis-porphyrin forms a cleft which, after complexation with Zn(II), acts as a receptor for a,o>-diaminoalkanes. For example 1,12-diaminododecane is bound with an association coiLstant of K. = 7.0 x 10 mol L. When a first-generation dendritic polyamine bearing four terminal primary amine groups is used as a guest, two receptor molecules assemble in such a way that they encapsulate the small dendrimer molecule, as in 50 (Figure 28). This was proven by titration studies, using H NMR and UV-vis absorption spectroscopy. 

As we have just seen, electrostatic interactions can reinforce the formation of axial base complexes in metalloporphyrins, but other thermodynamically favored processes, such as chelation around a bidentate base like pyrazine, can be used. This approach has led Kuroda to the preparation of self-assembled dendrimer-type structures 86-89 represented in Figure 13.50 ". In these structures, the zinc porphyrin dimer formed by multihydrogen bonding of tetracar-boxylate derivatives of TPP is considered as a chelate. 

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