Spectroelectrochemistry of porphyrin containing mono- and hetero-bimetallic systems:: Porphyrin-Ru(bpy)3 conjugates

The redox behavior of porphyrin-Ru(bpy)(3) conjugates is studied by means of spectroelectrochemistry. The redox potentials for the porphyrin freebase, zinc and manganese derivatives are measured and compared to the corresponding monomeric reference porphyrins. Among the porphyrin-Ru(bpy)3 conjugates, the manganese derivative behaved like its monomeric reference compound, the zinc derivative showed moderate differences, and the freebase derivative exhibited the largest differences. These results are understood to originate from the extended orbital overlap of the redox reaction centers. In the case of the freebase derivative, the bpy ligand of the Ru(bpy)(3) moiety is spacially very close to one of the porphyrin moiety's pi-system pyrroles, which is acting as a redox reaction center. For the zinc derivative this effect is more moderate; and because the redox reactions in the manganese derivative occur at the manganese central metal, which is too far from the bpy group, the effect is minimal. From the viewpoint of the Ru(bpy)3 moiety, the redox reactions of the Ru metal are not affected by the presence of the porphyrins due to the absence of Ru-porphyrin orbital overlap.