Interactions of Two Porphyrin Rings: Metal-Induced Structural Change of 5,5′-Ethylenebis(porphyrin)

5,5′-Ethylenebis(octaethylporphyrin) 1 and its metallocomplexes with various combination of metals (Zn, Cu, and Ni) 2—10 were prepared. On the basis of 1H and 13C NMR as well as MCD spectra, it was concluded that interactions between the two intramolecular porphyrins become attractive when at least one of the two rings is converted to zinc porphyrin. The phenomenon was explained by dipole–dipole interaction arising from the large polarization in Zn complexes.