Oxoporphyrinogen

Figure 40 Oxoporphyrinogens that, although not technically expanded porphyrins, are characterized by an extended jr-system. The result is highly colored species that are also highly sensitive to anion eomplexation.

We have chosen to divide the porphyrinoids into two famihes the peripherally functionalized porphyrinoids (e.g., N-confiised porphyrins, jr-extended porphyrins, oligo-porphyrins) and the coie-fimctionalized (nonplanar) por-phyrinoids (e.g., porphyrinogens, alkylidene porphyrins, oxoporphyrinogens, and some oligopyrroles). The former contains mostly molecnles that have complex elaboration at their periphery, which leads to special snpramolecular properties. Core-snbstituted porphyrinoids inclnde N-snbstituted oxoporphyrinogens and even some metalloporphyrins and porphyrin dications. 

Figure 13 (a) Chemical structure of a bis-porphyrin-oxoporphyrinogen conjugate with a unique N-alkyl linkage of porphyrins,... 

Bis(zinc porphyrin)-oxoporphyrinogen [(ZnTPP)2-OxP] is an example of a donor-acceptor-type triad. Excitation of the zinc porphyrin gronps leads to an efficient energy or electron transfer in the triad and this process depends on the polarity of the solvent used. Further elaboration of this system was accomplished by complexing this compound and other derivatives with fullerene-containing compounds capable of coordinating at the porphyrin zinc metal ions. The structures of the complexes are shown in Figure 14. 

Figure 14 Chemical structures and corresponding energy-minimized stracmres of snpramolecular complexes of the porphyrin-oxoporphyrinogens with bis-pyridyl-snbstitnted fuUerene, Py2C6o- (a) OxP-(ZnPp)2 Py2C60- (b) OxP-(ZnP )4 (Py2C6o)2-R = 3,5-bis(3-methylbutyloxy)phenyl.

Oxoporphyrinogen A porphyrinogen macrocycle substituted at its mexo-positions with oxo groups or hemiquinone groups. The compounds have an extended nr-system and are highly colored species, yet not technically porphyrins since the conjngation is not in a cyclic array. 

However, achiral oxoporphyrinogen works as a host capable of signaling chiral information of a-hydroxycar-boxylic acids in H NMR. Thus, enantiomeric excess ee) can be determined by observing the splitting of H NMR resonances of the achiral host. This differs from the case of chiral hosts (shift reagents) where % ee is generally determined from the ratio of peak areas as a result of diastereomeric host-guest complexes. The unusual phenomenon is based on formation of a complex with 1 2 stoichiometry in concert with a protonation-driven tautomerization of the host. 

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