The NMR spectra of the porphyrins. 36—Ring currents in octaethylporphyrin, meso‐tetraphenylporphyrin and phthalocyanine complexes

The change in ring current of octaethylporphyrin, meso ‐tetraphenylporphyrin and phthalocyanine cobalt(III) complexes with axial amine ligands was studied using a double dipole network model. The porphyrin ring current was found to be highest in octaethylporphyrin but decreased by 5% in meso ‐tetraphenylporphyrin and 29% in phthalocyanine. The ring current in the fused benzene rings of phthalocyanine was similar to that found in free benzene. An attempt was made to rationalize changes in the porphyrin ring current in terms of the porphyrin substituents. An existing ring current program, DIPCALC, was modified to allow the calculation of ring current shifts for phthalocyanines. The parameters required to calculate ring current shifts for all three porphyrins are presented.