Fullerene porphyrin/zinc complex

Fig. 6.51 Dendritically linked porphyrin/zinc complexes with fullerene at the focal point (according to Aida et al.)...

In a supramolecular approach to fullerene-porphyrin hybrids, the assembly of a rigidly connected dyad, in which a zinc tetraphenylporphyrin, Zn(TPP), is noncovalently linked to a C60 derivative via axial pyridine coordination to the metal, was reported [219-222]. Photo excitation of the dyad Zn-complex led to electron transfer with very long lifetimes of the charge-separated pairs, as revealed by optical spectroscopy and confirmed by time-resolved electron paramagnetic resonance spectroscopy. Accordingly, two different solvent-dependent pathways can be considered for the electron-transfer processes. Either the excitation of the porphyrin chromophore is followed by fast intramolecular electron transfer inside the complex, or alternatively the free porphyrin is excited undergoing intermolecular electron transfer when the acceptor molecules ap-... 

Figure 5.56 Schematic illustrating the self-assembled multilayers of sodium 3-mercaptoethane-sulfonate (layer 1 ), hexacationic homooxacalix[3]arene-fullerene (2 1) complex (layer 2 ), with either the anionic porphyrin polymer ( 3 ) or its zinc porphyrin analogue ( 4 ) forming the third layer. Reprinted with permission from A. Ikeda, T. Hatano, S. Shinkai, T. Akiyama and S. Yamada, /. Am. Chem. Soc., 123,4855 (2001). Copyright (2001) American Chemical Society...

Bis(zinc porphyrin)-oxoporphyrinogen [(ZnTPP)2-OxP] is an example of a donor-acceptor-type triad. Excitation of the zinc porphyrin gronps leads to an efficient energy or electron transfer in the triad and this process depends on the polarity of the solvent used. Further elaboration of this system was accomplished by complexing this compound and other derivatives with fullerene-containing compounds capable of coordinating at the porphyrin zinc metal ions. The structures of the complexes are shown in Figure 14. 

Notably, this metal-mediated concept, namely, coordination of a fullerene-pyridine ligand by a macrocyclic r-system, is very general and has been successfully extended to zinc complexes of phthalocyanines, porphycenes and corrphycene macrocycles. Interestingly, the binding strength reveals a close resemblance to the oxidation potential of the macrocyclic s -system porphycene > porphyrin. 

As with chromophores, the steric encapsulation of a dendrimer core can be utilized to prevent intermolecular interactions between redox active sites. A number of different redox active core moieties have been investigated, including, iron—sulfide clusters,9394 bis(terpyridine)iron(II) complexes,92 tris-(bipyridine)ruthenium(II) complexes,330 zinc porphyrins,252 oligothienylenevinylenes,331 fullerenes,236,332 ferrocenes,333-336 oligothiophenes,322 oligonaphtha-lenes,337 and 4,4 -bipyridinium.338... 

Aida et al. noticed that zinc porphyrin (ZnP) cyclic dimer formed an inclusion complex with Cgo, stable enough to remain associated even under chromatographic conditions. The cyclic dimer model was further extensively studied to improve the association binding constants and thus the selectivity with fullerenes. An exhaustive report of this work has been published recently. ... 

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