Metalloporphyrins photochemical properties

Photodyncimics of metalloporphyrins have been extensively investigated on account of its importance in the understanding of photosynthesis and other processes of biological importance ( ). Particular atten-sion has been paid to the reason why the excited metalloporphyrins possess unique characteristics from the viewpoint of redox (2-4), energy transfer ( ), and other photodynamical processes (6,7). In comparison with the considerable knowledge accumulated on the photochemical properties of the lowest excited states, little has been known on the S2 - Sq fluorescence and Si Sq internal conversion processes which can also be regarded as unusual characters of metalloporphyrins. 

Metalloporphyrins electrical properties, 144 in oxygen production from water, 522 photochemical properties, 510 in photoproduction of hydrogen from water, 511, 510-513 structure, 615 Mctallothioncins cobalt(II), 673 copper and zinc storage, 672 EXAFS, 673 mammals... 

Metalloporphyrin-based MOFs have also been investigated for light-harvesting and photochemical properties [53,54]. In 2011, Wu et al. reported the synthesis of a tin-porphyrin-derived MOF [Zn2(H20)4Sn (TPyP)(HC00)2l 4NO3 -DMF4H20 (11, Sn TPyP = 5,10,15,20-tetra(4-pyridyl)-tin(IV)-porphyrin) [55]. 11... 

The electron transfer proceeded with the participation of the triplet excited state of Chi. The discovery of the reversible reaction of chlorophyll photoreduction served as a stimulus for starting systematic research on photochemical redox reactions of chlorophyll and its synthetic analogs, i.e, various metalloporphyrins (MP). For a review of the physical and chemical properties of MP, see, for example, Ref. [62]. 

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). 

These complexes are kinetically labile and display characteristic structural and photoinduced properties that strongly deviates from those of the regular metalloporphyrins. The latter kind of structure induces special photophysical and photochemical features that are characteristic for all SAT complexes. The symmetry of this structures is lower (generally C4V-C1) than that of both the free-base porphyrin (D2h) and the regular, coplanar metalloporphyrins (D4h), in which the metal center fits into the ligand cavity. 

Many chemical model systems based on metalloporphyrin catalysts and mimicking cytochrome P450-dependent monooxygenases have been described during these last decade. Several review articles have been devoted to these systems 2-10. in that context, very recent results about the preparation and catalytic properties of new homogeneous and supported catalysts will be described in a first chapter. In the second chapter, some preliminary results showing that the oxidation of alkanes by a dioxygenase-like mechanism could occur in the presence of iron porphyrin catalysts activated either photochemically or thermally, will be reported. 

Among the fundamental photophysical and photochemical processes, electron transfer has a high priority. Porphyrins and metalloporphyrins form one of the most promising series of chromophoric compounds for designing suitable redox systems as described above, since they have intense visible absorption bands and the can be varied by the substituents and the central metal ions. The redox properties are also easily regulated according to purpose. In recent intensive studies on electron transfer by various approaches from the viewpoints of theory. 

In this review, we restrict ourselves to metal-mediated assemblies of functional 7T-systems, which absorb light in the visible region (i.e. A. > 400 nm). Thus, materials whose color arises from metal ions or metal-ligand charge transfer (MLCT) are not included here. Self-assembhes derived from free base porphyrins, metalloporphyrins and perylene bisimide dyes have shown promising applications in artificial LH systems. Therefore, some fundamental properties of a few representative chromophores, namely meso-tetraphenylporphyrin (TPP), zinc tetraphenylporphyrin (ZnTPP), tetra-phenoxy-substituted perylene bisimide (PPBI) and bay area imsubstituted perylene bisimide (PBI), are briefly summarized herein. These properties are essential for the understanding of the photophysical and photochemical behavior of assemblies derived from such dyes. 

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