7r-System

The ligand group can be introduced either on the meso or on the /5-pyrrole position of the porphyrin ring, but the synthesis of the meso-functionalized derivatives is easier and has been more widely exploited. Balch (50-53) reported that the insertion of trivalent ions such as Fe(III) (32) and Mn(III) (33) into octaethyl porphyrins functionalized at one meso position with a hydroxy group (oxophlorins) leads to the formation of a dimeric head-to-tail complex in solution (Fig. 11a) (50,51). An X-ray crystal structure was obtained for the analogous In(III) complex (34), and this confirmed the head-to-tail geometry that the authors inferred for the other dimers in solution (53) (Fig. lib). The dimers are stable in chloroform but open on addition of protic acids or pyridine (52). The Fe(III) octaethyloxophlorin dimer (52) is easily oxidized by silver salts. The one-electron oxidation is more favorable than for the corresponding monomer or p-oxo dimer, presumably because of the close interaction of the 7r-systems in the self-assembled dimer. 

The sequence of operations involved in a PPP-MO calculation is illustrated in the flow diagram shown in Figure 2.13. The method is illustrated for the case of 4-aminoazobenzene, 15c. The first step involves devising a numbering system for all of the atoms that contribute to the 7r-system of the molecule. Secondly the total number of 7r-electrons in the... 

Planar coordination compounds with aromatic ligands, especially those having extended 7r-systems, show 7r-7r interactions in the solid state. The ligands shown in Figure 8 form complexes with silver(I) which have a supramolecular structure through 7r-7r interactions.586-596... 

A porphyrin compound with a 2,9-dimethyl- 1,10-phenanthroline functionality fused at the beta-pyrrole positions is a phthalocyanine analog, and formed a complex with zinc in the cavity and a further zinc binding to the phenanthroline group. The absorption and emission spectra of the compound with and without the external zinc demonstrated the strong effects of the second metal binding on the porphyrin 7r-system.840... 

On account of their particularly extensive delocalized 7r-systems, MPs have received comparatively more attention for their cubic, as opposed to quadratic, NLO properties. From the viewpoint of practical applications, such complexes (and also metallophthalocyanines and other closely related compounds) are of major interest for OL due to their tendency to exhibit RSA behavior. These materials are particularly well suited in this regard because they often exhibit strongly absorbing, long-lived triplet excited states as well as reasonably wide transparency windows over the visible region of interest between the intense B- and Q-bands. 

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