Metalloporphyrin complexes with a photochromic axial ligand were synthesized and photoisomerization behavior of those complexes was investigated. In this study, 3,3 ' azopyridine (AZP) was used as the axial ligand. We found that the structure of the axial-coordinated complexes depended on the center metal of porphyrin. When magnesium was employed as the center metal, a 1: 1 coordinated complex was obtained. On the other hand, zinc or rhodium porphyrins formed the sandwich-bonded complexes. The photoisomerization behavior also depended on the center metal of the porphyrins, and the cis-to-trans "one-way" photoisomerization of the AZP axial ligand took place in the complexes of zinc and rhodium porphyrins. The one-way isomerization may be interpreted as the results of the photoinduced electron transfer from porphyrin to AZP. (c) 2005 Elsevier B.V All rights reserved.