Metalloporphyrins electrostatic assembly

The most used approaches for the construction of multiporphyrin systems are the self-assembly methods. For example, electrostatic assembly is an easy and widely used method based on the interaction of oppositely charged porphyrins for preparation of more complex systems [1-12]. Self-assembly of porphyrins are also possible by coordination of nucleophihc groups to the central metal ion or using compounds having two nucleophihc sites to coordinate two metalloporphyrins [13-22]. These methods have been used not only for the preparation of porphyrin dimers and trimers, but also for the formation of larger supramolecular networks. Despite the apparent simphcity of the preparation methods of multiporphyrin materials by self-assembly, they generally are less stable as compared to covalently bond... 

Figure 4.15 Schematic representation of the sequential steps taken for the formation of multilayers based on electrostatic self-assembly using cationic polymers and anionic a-ZrP sheets (see text for further details). Reprinted from Coord. Chem. Rev., 185-186, D.M. Kaschak, S.A. Johnson, C.C. Waraksa,J. Pogue and T.E. Mallouk, Artificial photosynthesis in lamellar assemblies of metal poly(pyridyl) complexes and metalloporphyrins, 403-416, Copyright (1999), with permission from Elsevier Science...

Porphyrins and metalloporphyrins exhibit planar, relatively rigid structures suitable for the preparation of materials displaying cavities or that can self-assemble by electrostatic and n-n interactions. They also provide very interesting functional building blocks because of their rich coordination, catalytic, electro-catalytic, photochemical, and redox properties, as described in many papers (100-102) and review articles by Toma and co-workers (31,38,39), Latos-Grazynski et al. (103), Imamura and Fukushima (104), Sanders (105), Chambron et al. (106), Baldini and Hunter (107), and Prodi et al. (108). 

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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