Cages, porphyrins

Jin R-H, Aida T, Inoue S (1993) Caged porphyrin the first dendritic molecule having a core photochemical functionality. J Chem Soc Chem Commun (16) 1260-1262... 

Crossley (89) described the self-assembly of a spherical cage-like structure made up of two zinc porphyrin dimers bound to a tetramine ligand. The 2 1 complex is stable at 10-6m concentrations, but addition of excess of ligand causes dissociation of the capsule with formation of a 1 1 complex. 

Aida and Jiang recently reported an iron(II) porphyrin 1-methylimidazole complex covalently encapsulated within a large aryl ethereal dendrimer cage, as... 

J.R. Bolton In solution most photochemical electron transfer reactions occur from the triplet state because in the collision complex there is a spin inhibition for back electron transfer to the ground state of the dye. Electron transfer from the singlet excited state probably occurs in such systems but the back electron transfer is too effective to allow separation of the electron transfer products from the solvent cage. In our linked compound, the quinone cannot get as close to the porphyrin as in a collision complex, yet it is still close enough for electron transfer to occur from the excited singlet state of the porphyrin Now the back electron transfer is inhibited by the distance and molecular structure between the two ends. Our future work will focus on how to design the linking structure to obtain the most favourable operation as a molecular "photodiode . 

Metalated container molecules can be viewed as a class of compounds that have one or more active metal coordination sites anchored within or next to a molecular cavity (Fig. 2). A range of host systems is capable of forming such structures. The majority of these compounds represent macrocyclic molecules and steri-cally demanding tripod ligands, as for instance calixarenes (42), cyclodextrins (43,44), and trispyrazolylborates (45-48), respectively. In the following, selected types of metalated container molecules and their properties are briefly discussed and where appropriate the foundation papers from relevant earlier work are included. Porphyrin-based hosts and coordination cages with encapsulated metal complexes have been reviewed previously (49-53) and, therefore, only the most recent examples will be described. Thereafter, our work in this field is reported. 

Fujita and coworkers have also reported the encapsulation of multimeric porphyrin assemblies in the box-shaped cavities of ternary Pd6 coordination cages. Two types of cofacial porphine dimers A and B could be stabilized (133). In the smaller [Pd6(L14)2(L15)6]12+ cage 29, whose diameter is 10.4 A (Fig. 21), two porphyrin molecules can be stackedo directly on top of each other with an interplane distance of 3.4 A. In the larger cage 30, an additional molecule of L14 is intercalated between the two porphyrin bases. All complexes were found to be water-soluble in contrast to other 7i-stacked porphyrin dimers. The encapsulation... 

Fig. 21. The two types of cofacial porphyrin dimers A and B and the chemical structures of the coordination cages 29 and 30 (133).

Therefore, the simplest strategy to increase the water solubility of C2B10-containing compounds is degradation of the closo-cage to the nido-anion, and this has been applied to C2Bio-containing amino acids and porphyrins (see Scheme 2.2-13). 

Figure 3.7 [ 55 5 2(4- ) 6( ) ] cluster confined within a six-zinc porphyrin cage. 

Lee J, Park YS, Kim YI, et al. Synthesis of a porphyrin having eight carborane cages. Bull Korean Chem Soc 1999 20(11) 1371-1372. 

In Ref. [317] the temperature independence of the intramolecular electron transfer reaction in a cofacial Zinc porphyrin-quinone cage molecule was observed in the range 80-300 K and interpreted in terms of non-adiabatic electron tunneling. 

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