B.S., 1970; M.S., 1975; Ph.D., 1977, University of Wisconsin (Inorganic Chemistry (D. F. Gaines); Postdoctoral Fellow, UNC-Chapel Hill, 1977-1979 (T. J. Meyer); Assistant Professor, Lafayette College, 1979-1983. Chemical engineer, Texaco, Inc. 1970-1971. UNCG Department of Chemistry and Biochemistry ,1983-present.

RESEARCH PROGRAM

The preparation of model chemical compounds to evaluate their fundamental electronic and structural characteristics is the standard approach to defining the role of more complex chemical systems. Our research group is involved in synthesis of coordination complexes for the purpose of modeling the behavior of metal centers in biological systems or in systems being evaluated for artificial photosynthesis. Our focus is on the preparation of coordination complexes where the metal center and ligands can act in concert to promote electron transfer reactions. Electron transfer processes are fundamental to the initiation of photosynthesis¹ and to the photochemical activation of artificial photosynthesis systems.²

The present focus of our work involves the use of polypyridyl ruthenium complexes containing sulfur donor or ferrocene-centering ligands. Each of these classes of compounds contain redox active ligands that can act in concert with the electron transfer properties of the ruthenium center. In addition, this type of ruthenium center has been found to have long lived excited states, so the incorporation of light absorption, excited state electron transfer, and ligand trapping of redox equivalents becomes a possibility. 

The research involves synthesis of coordination complexes of ruthenium by standard bench top techniques. Characterization by NMR, IR, UV-VIS, emission, and fluorescence spectroscopy and by electrochemistry is used to define the structure, properties, and reactivity of the complexes.

For example, Ru (Fctrpy)₂²⁺ (Fctrpy = ferrocenyl-terpyridine, (I)) is a 6 coordinate complex of ruthenium(II) with each trpy moiety binding to three coordination sites. Redox studies show that the appended ferrocenes and the ruthenium center behave independently. However, when the ruthenium center absorbs light energy, exciting a ruthenium electron, the ferrocenyl group rapidly quenches the excited state. A related observation has shown that photoexcitation of the complex may lead to decomposition of the ferrocenyl unit.

RESEARCH PROJECTS

Photochemistry of Ferrocenyl-substituted Polypyridyl Species

Observations described above and literature information suggest that substituted ferrocene species may show surprising photochemical activity. The attachment of a cationic pyridyl species such as a pyridinium or a metal-coordinated pyridyl species to the ferrocene seems to activate the ferrocene toward photochemical or oxidative decomposition.

Complexes Containing Sulfur Donor Ligands

            (II)                           (III)                                                          (IV)                                                          (V)

Thiolate species undergo oxidation to form disulfide bridged oxidation products (Eq. 1).

2 R-SH R-S-S-R + 2H⁺ (1)

Dithizone undergoes two oxidative processes: disulfide bridge formation as in Eq. 1 and formation of a tetrazolium species. (V)

In these studies we are investigating the influence of the sulfur donor ligand on the photochemical properties of the polypyridyl system and the influence of coordination on the sulfur-centered redox chemistry of the sulfur donor ligand.

Overall the research involves synthesis of ligands, synthesis of metal coordination complexes, characterization of the species formed, investigation of spectral and photochemical properties of the coordination complexes, and electrochemical characterization of proposed species.

CHEMICAL EDUCATION

Work in this area involves development of general chemistry laboratory experiments, supporting materials for laboratory, and professional development programs for teachers. A current project is a collaboration with the School of Education in presenting the NCQuest project “Teachers Teaching Teachers". This project establishes learning communities in high school that foster high quality science education. Another current project, "POST" (Preparing Outstanding Science Teachers) supports professional development for middle school teachers and promotes the inquiry approach to science teaching.