Porphyrins covalent dimers

Figure 39. Supramolecular w tems 76 and 77 result from the coordination of porphyrin 64 to p-phenylene-bridged Zn(ll) porphyrin covalent dimers.

Monomer (mZnPn) and dimer (dZnPn) Zn porphyrins. Porphyrins in dimers covalently linked by two 4-, 5-, or 6-atom long chains. Measurements performed at 1.3 K. (8)... 

Fig. 20 Supramolecular assembly of 26 formed via heteroassociation of an imidazolyl-substituted porphyrin-phthalocyanine covalent dimer...

Among all the single Co porphyrins examined, a [3-pyrrole substituted species bearing two ester groups, mentioned briefly in Section 3.1.2, (see insert, Figure 3.51) was found to display a rather unique behavior upon adsorption on carbon surfaces. This macrocycle, to be denoted as CoPI, is a precursor to the synthesis of the first face-to-face porphyrin examined in an electrochemical environment [95] hence, a discussion of its properties serves to underscore the effects associated with changes in the electrocatalytic microenvironment following covalent dimerization (see below). 

Recently, we have shown that the supramolecular approach (a non-covalent two-fold extra-ligation in conjunction with Zn-porphyrin chemical dimers and trimers) can be successfully employed to create a variety of multiporphyrin structures capable of the fast effective intra-complex energy migration and photoinduced electron transfer [5]. Following this self-assembly principle we have succeeded to anchor in pyridyl substituted porphyrin molecules on CdSe/ZnS QD surfaces. In this case, CdSe/ZnS QDs show luminescence quenching induced by dynamic and/or static interactions between QD and porphyrins depending critically on sample stability, temperature and solvent polarity [6]. The general focus of this contribution is devoted to demonstrate the... 

In covalent dimers, the bridging element between the two chromophores may restrict the respective orientations of the two chromophores, and thus, influences the degree of their electronic coupling. In the absence of abridge, the degree of electronic coupling between two porphyrins linked directly at the meso position can still be controlled by the peripheral substitution. Indeed, the peripheral substitution can affect the nature of HOMO frontier orbital. 

Specifically Netzel et al. ( - ), in studies of face-to-face , covalently-linked MgP-P dimers, found evidence for the formation within 6 psecs of a low-lying, relatively long-lived intramolecular CT state of the type MgP -P" in polarizable or highly polar solvents and in solvents where chloride ion coordinates with the magnesium ion of the MgP-macrocycle. These workers also observed the formation of benzoquinone anion radicals as stable photoproducts of the CT formation process when the experiments were carried out in the presence of benzoquinone ( ). This approach provides a more direct test for the formation of an intramolecular CT state, and the results are in sharp contrast to those typically observed when porphyrin Ktt, ) states are quenched in the presence of benzoquinone (23). 

Synthesis, purification and identification of cyclopentanporphyrins and their chemical dimers covalently linked via isocycles have been described in previous papers (17,19-23). The porphyrins with the cyclopentanone ring have been prepared by familiar methods (24-26). 

It should be noted that the existence of different centers Is also found in covalently-linked dimer 11. Moreover, the analysis of all data obtained for dimers points clearly towards the efficient transfer of the excited singlet state energy from two centers of compound 1 to two acceptor centers of compound 2 in dimers (14,30). Increase In the porphyrin concentration by 300-700 times (say, for compounds 1 and 2) does not cause additional changes In electronic spectra as against diluted solutions. If the results obtained from temperature experiments (Fig. 2b) and measurements of fluorescence lifetimes In different bands are taken Into account, one may conclude that the additional centers observed In... 

In the present work, we used a conformationally flexible covalently-linked porphyrin dimer (5,5-[1,3-Propenediyl bis(oxy-2,l-phenylene)]bis[10,15,20-tris(4-methylphenyl)-21H,23H-porphin](0,0 -C (TTPH2)2) The dimer is mainly in two different conformations. 

The above three studies on the synthesis of oxygen carriers are of great significance because they have demonstrated steric and environmental effects on reversible oxygenation. Recently the porphyrin ring was perfectly bonded to a polymer by a covalent bond in order to inhibit the dimerization of the porphyrin complex. 

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