Metalloporphyrins hypso type

Additional Material on Metalloporphyrins of the Spectral Hypso Type.113... 

Fig. 2. The three main types of metalloporphyrins spectra 1. Normal spectrum [upper part, solid line, Zn(OEP)] 2. Hypso spectrum [upper part, dashed line, Pt(OEP)] 3. Hyper spectrum [lower part, Fe(OEP)F). The data are taken from Ref. [24). The bands of the normal and hypso type are labeled a, 0, and S ( Soret ), those of the hyper type are given roman numerals increasing with their energy because their assignment is frequently ambiguous...

The hyper type and the hypso type may occur in mixed versions (61). The hypso type has not always been recognized as an individual spectral type by other authors, and, concomitantly, the importance of metal-to-porphyrin backbonding has been neglected (46, 48). The present scheme cannot explain why some large alkaline earth cations cause bathochromic shifts as long as a definite structural characterization of these metalloporphyrins is missing (20-22). 

The four-orbital model of the porphyrin spectra as applied by Gouterman (49-50) also serves to explain the mechanism of metal-to-porphyrin backbonding in metalloporphyrins of the spectral hypso type. This backbonding has been invoked for these complexes by Williams (45) and Falk (20). 

Oxidation of the central metal reduces the availability of the d -electrons thus in the recently prepared Pt(TTP)Cl 2 ([20], M = Pt, L = X = Cl 68) the /3-band suffers a bathochromic shift from 510nm to 538 nm, but this value still implies a hypso type and thus residual dll-eg(7r ) backbonding in the PtIV porphyrin in accord with the other d6 systems (24). If axial ligands are attached to a metalloporphyrin of the... 

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). 

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

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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