Metalloporphyrins regular

The absorption spectra of metalloporphyrins are classified into three types, regular, hypso and hyper, and summarized as follows.4... 

Coordination of metal ions often has a dramatic effect on the n delocalization in porphyrins and porphyrinoids. It has particularly conspicuous influence on the electronic spectra of metalloporphyrins, which show a dependence on the identity of the metal ion, axial ligation, oxidation level, and spin state. In regular porphyrins, metal coordination reduces the number of observed Q bands from four to two, reflecting the higher symmetry of the chromophore relative to the free base. However, detailed quantitative information on the Jt-electron delocalization is more easily accessible from other physical methods. 

Fig. 5. Absorption spectra of (a) H2TPP (full line) and H2TF2PP (dashed line) (b) H2TCl2PPethyl (full line) and H2TFPBmethyl (dashed line) and (c) Zn TPP (regular metalloporphyrin, solid line), Cu TPP (hypso-type spectrum, dashed line), and Mn TPPCl in toluene (hyper-type spectrum, dotted line). 

III. Some General Remarks on the Oxidation States of Metalloporphyrins (Electronic Spectra, esr Spectra, Electrochemical Regularities)... 

Indeed, the correlation of the electronic spectra with different metallo-porphyrin states is not unequivocal in many specific cases. The distinctions between 2 and 4 are not clearcut, as is the case with 5, 8 and 9. Further complications arise when the metalloporphyrin aggregates, which usually leads to absorption-band broadening. In many of these cases magnetic data will provide additional evidence, or certain electrochemical regularities (see V.l) can be used. 

In a different reaction scheme, one can take advantage of the fimctional porphyrin macrocycle to create metalloporphyrin compounds and nanoarchitectures in 2D. Upon exposure of regular TPyP arrays self-assembled on Ag(lll) to iron monomers supplied by an atomic beam, selective com-plexation occurs whereby the template structure is strictly preserved [156]. This expands the diversity of metalloporphyrin layers conventionally realized by evaporation of integral species, because in-situ metalation provides a route towards novel metalloporphyrin nano architectures and patterned surfaces [156-158]. In a related reaction pathway, evidence could be obtained for in-situ complexation and metal center-induced switching of phenanthroline-based catenane units deposited the Ag(lll) surface [182]. 

Since our original article was written, a regular series of reviews of porphyrin chemistry has begun two books on the chemistry of pyrroles, a second edition of Porphyrins and Metalloporphyrins (based on Falk s original book), and a small handbook concerned with laboratory methods and spectroscopic data have now appeared. A seven-volume treatise on the chemistry and biochemistry of porphyrins has also recently been published volumes 1 and 6 are particularly relevant to the subject matter of this article. 

Regular metalloporphyrin complexes fluoresce, with their fluorescence quantum yield modified by the heavy-atom effect. The complexes tend to be purple in the solid state and wine red in solution. The normal absorption spectra of regular porphyrins is indicative of little or no interaction between atomic orbitals on the metal and ir-molecular orbitals on the porphyrin. Thus, the absorption and emission spectra of regular metalloporphyrins are largely determined by the porphyrin s ir-electrons. This is not the case with irregular metalloporphyrins. They show three main types of spectra called normal, hypso, and hyper. 

Depending on their size, charge, and spin multiplicity, metal ions (e.g. Zn, Cu, Ni, Co, etc.) can fit into the center of the planar tetrapyrrolic ring system forming regular metalloporphyrins resulting in a kinetically inert complexes (Fig. 10a). 

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. 

In Figure 12 is shown a schematic Energy-level diagram of the frontier orbital of a porphyrin in free-base state (H2P), in a regular and in a SAT metalloporphyrin. 

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