Binding of bis-(Diimine)-Carbonyl-Osmium(II) Compounds to Porphyrins Through Pyridine and Imidazole Linkages
Elise G. Megehee and Alison G. Hyslop, St. John’s College of Liberal Arts and Sciences, Department of Chemistry
Abstract: Upon excitation of ultraviolet light into a bipyridine p-p* band, bis-(2,2’-bipyridine)-carbonyl-(5-pyridyl-10,15,20-triphenylporphyrin)-osmium(II) exhibits energy transfer as evidenced by emission from only the porphyrin half of the molecule.1 When the protons inside the porphyrin are replaced by zinc, the emission is shifted and mainly quenched suggesting that electron transfer may occur. We are currently characterizing four series of compounds of the form [Os(NN)2CO(L)](PF6)2 to study the effect of ligand variation on the electronic properties. In each cases we are varying the diimine ligand (NN): 1) L = pyridine; 2) L = 4-phenylpyridine; 3) L = 5-pyridyl-10,15,20-triphenylporphyrin; and 4) L = 5-pyridyl-10,15,20-triphenylporphyrin zinc(II). More recently in order to probe this interaction, we have replaced the pyridine with various imidazole ligands. Eventually we will attach a porphyrin to the end of the imidazole ligand to study the electronic communication between the two moieties. We will discuss the synthesis and electronic characterization of these compounds.
1A. G. Hyslop, M. Orphanide, U. Javed and E. G. Megehee, Inorganica Chimica Acta, 2003, 355c, 285-292.