Xie, Y.; Lei, Y.; Shah, S.; Wu, H.; Wu, J.; Megehee, E.; Wang, E. Investigation of Luminescence Characteristics of Osmium(II) Complexes in the Presence of Heparin Polyanions. Int. J. Anal. Chem. 2013, 2013 (Copyright (C) 2017 U.S. National Library of Medicine.), 419716.
My research focuses on fundamental research of osmium and ruthenium complexes that have the potential for use in 1) converting sunlight into chemical energy or electricity and 2) detecting DNA and small anions as sensors. These osmium and ruthenium complexes absorb visible and ultraviolet light, and then transfer this energy to other molecules (energy transfer) or use the energy to move electrons between molecules thus generating a current (electron transfer). When coupled to porphyrin molecules, the can be used to mimic photosynthesis. These molecules can also be used to detect the presence of DNA at very low levels in solution which makes them good candidates for sensing devices. Much of our research involves the synthesis and characterization of novel complexes. I currently have six research projects under way in my laboratory, several of which are now complete and will be submitted for publication this year. The remaining projects are at various stages and while they did not lead to publication this past year, many of them are coming to fruition and should lead to publications in the coming year or two. Three of these projects involve using the bis-(Diimine)-Carbonyl-Ruthenium(II) moiety as the starting point and varying the sixth ligand. Two involve using the bis-(Diimine)-Carbonyl-Osmium(II) moiety as the starting point and varying the sixth ligand The last project utilized a dicarbene ligand.
Project 1 uses the bis-(Diimine)-Carbonyl-Metal(II) (where M = osmium and ruthenium, diimine = 2,2’-bipyridine or 1,10-phenanthroline) and has 5-pyridyl-10,15,20-triphenylporphyrin or 5-imidazole-phenyl-10,15,20-triphenylporphyrin as the sixth ligand. This is part of an ongoing collaboration that I have with Dr. Alison G. Hyslop. These complexes are of interest because they exhibit energy and/or electron transfer between the porphyrin and the metal center and may be of use in light harvesting processes such as solar energy collection and storage panels.
Project 2 is related to 1 except that is involves using pyridine and substituted pyridine derivatives as the sixth ligand. I currently have two students working on the synthesizing and purifying the ruthenium complexes. Manuscripts are in preparation for the osmium analogs where L = pyridine, 4-phenylpyridine, and 5-pyridyl-10,15,20-triphenylporphyrin complexes.
Project 3 involves using the bis-(Diimine)-Carbonyl-Metal(II) (where M = osmium and ruthenium, diimine = 2,2’-bipyridine or 1,10-phenanthroline) with various imidazoles as the sixth ligand. Imidazoles are stronger binding ligands compared to pyridines, so should form a more stable complex with the osmium. Several of the osmium analogs have been synthesized and characterized. I currently have a Master’s student synthesizing and characterizing the ruthenium complexes.
Project 4 involves the use of a potentially bridging diimine ligand as the sixth ligand. This project is in collaboration with Dr. Alison Hyslop and Dr. Gina Florio as these complexes can be used to bind to metals inside porphyrins or to bind to metal surfaces, respectively. Many of the osmium complexes have been synthesized and characterized, but the ruthenium analogs are currently being studied by two Master’s students.
Project 5 involves the synthesis and characterization of the mixed ligand complexes of ruthenium(II) with diimines and n-heterocyclic bis-carbenes. This is a collaboration with Dr. Richard Rosso combining my expertise in transition metal bipyridine complexes and Dr. Rosso’s expertise in n-heterocyclic carbenes. These complexes are important analogs of ruthenium tris-bipyridine, the standard for luminescent transition metal complexes. These ligands have been shown to be quite stable on other metal centers, but have to date not been used on ruthenium bipyridine or ruthemium phenanthroline complexes. One former and one current student have worked on synthesizing, purifying, and characterizing these novel dicarbene complexes.
Project 6 has an organic hydrocarbon group as the sixth ligand. These compounds are of interest as they are one of the few cases where two different isomers, same atoms but different arrangement about the metal center, are obtained in one synthesis. The cis-isomer is stable in the presence of visible light, while the trans-isomer reacts upon exposure to light. The light induced chemistry of the trans-complexes could potentially lead to interesting nanomaterials such as molecular wires which have potential use in electronics. Research by several MS students show that the trans-isomer is the kinetic product and the cis-isomer is the thermodynamic product.