Regular porphyrins

Finally, the isoporphyrins with a nitrogen atom inverted from the inner core into a /5-pyrrolic position can be prepared by classical porphyrin synthetic routes when the pyrrolelinking CH2X or formyl group is attached to the /J-position of the pyrrole subunit instead of the a-position of the pyrrole as in the synthesis of regular porphyrins. 

Most of the porphyrinoid molecules synthesized so far possess a number of peripheral substituents. In fact, many of the important macrocyclic systems were obtained with several distinct substitution patterns. Usually they correspond to one of the generic substitution types of regular porphyrins meso-aryl or p-alkyl, as exemplified by 5,10,15,20-tetraphenylporphyrin and 2,3,7,8,12,13,17,18-octaethylporphy-rin, respectively (Fig. 2). For the sake of brevity we will assume the following conventions in the entire manuscript ... 

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. 

Prototropic tautomerism in porphycenes exhibits characteristics that are vastly different from the behavior of regular porphyrins and has therefore been researched using a variety of techniques, including high-level electronic spectroscopy methods [41], Initial 15N CPMAS NMR experiments carried out on 30a revealed that proton... 

FIG. 3 Jablonski energy level diagram for a regular porphyrin, illustrating the photophysical... 

Electronic absorption spectra for o-bonded complexes of cobalt rhodium , thal-lium silicon germanium °), and tin are characteristic of regular porphyrins. 

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. 

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