MOLECULAR-ORGANIZATION OF PORPHYRIN-METAL COMPLEXES

Tetraethyltetramethylporphyrin substituted at two facing meso position s by N-methylimidazolyl groupings and its metal complexes were prepare d. The absorption spectra of Zn and Mg complexes showed a characterist ic splitting of Sorer band and red-shifts of Q-bands indicating the ex citon interaction of porphyrins in a slipped cofacial arrangement, whe re each imidazolyl group in one metal porphyrin is coordinated to meta ls in the other porphyrin skeleton. Typical upfield shifts in the H-1 NMR spectra arising from such the stacking structure elucidated Zn and Mg complexes as a dimer and an oligomeric mixture, respectively. Bis( imidazolyl)substituted tetraethyltetramethyl-porphyrin was also prepar ed. It suggested the hydrogen bonded oligomer formation through imidaz olyl-imidazolyl interactions in a columnar orientation. Electric condu ctivities of films prepared from these compounds were characterized. I n a same Line with behaviors in solution, samples capable of pi-stacki ng interaction with adjacent porphyrins via ligand-to-metal coordinati on or hydrogen bonding exhibited higher conductivities as well as lowe r activation energies for the thermal conduction. These behaviors are understood as due to the overlap of pi-systems of one porphyrin with n eighboring porphyrins.