Dennis P. Strommen
Ph.D. Inorganic Chemistry, Cornell University – 1971
Research area: Raman Spectroscopy, Solar Energy Conversion
1) Photosensitizers and Photochemistry
Solar energy conversion schemes are many and varied, but one common thread connecting all of them is that there must be a light harvesting device (photosensitizing molecule). The paradigm for most studies is [Ru(bpy)2+, where [Ru(bpy)2+ = tris-(2,2'-bipyridyl) ruthenium (II).
The first excited state of this molecule, [Ru(bpy)2(bpy. )2+ , where an electron from the Ru has moved to one of the three bipyridine moieties, is readily able to transfer an electron to other molecules and ions that are at lower energies. This process can ultimately result in the production of useful work Our research focuses primarily on establishing methods and strategies to probe the nature of these excited states. One of the most interesting findings is that the lifetime of the excited state of the paradigm is highly sensitive to particular sites of deuteration. We are currently attempting to synthesize various deuterated analogues of the related diazines. ie...4,4' bipyrimidine.
Addition of microwave synthesizer has opened the possibility of new and exciting synthetic routes. Individual projects are focused on preparations and lifetime determinations.
2) Normal Coordinate Analyses
Raman spectroscopy is a light scattering technique that is ideal for studying molecular vibrations of both the excited and ground states of photosensitizers. Although there are numerous quantum mechanical techniques available for determining the nature of vibrational modes, the most direct method involves classical mechanical techniques referred to as the Wilson GF matrix approach. Its main limitation is that one searches with a limited number of observables for a unique solution on a hypersurface of higher order. Thus the problem is under-determined. The observables are the frequencies of the normal vibrations while the order of the hypersurface is determined by the number of force constants. By obtaining deuterated analogues of the parent molecule, we can effectively increase the number of experimentally determined parameters and solve the equations for a more unique solution. Thus the purpose of the research in 1) becomes clear. Projects in this area involve extensive use of computers and laser spectroscopy.
"Laboratory Raman Spectroscopy," K. Nakamoto, D.P. Strommen, John Wiley and Sons, 1984.
"Position-Dependant Deuteration Effects on the Non-Radiative Decay of the 3MLCT State of Tris-Bipyridine Ruthenium (II) and the Identification of the Critical Acceptor Mode," K. Maruszewski, K. Bajdor, D.P. Strommen, J.R. Kincaid, J. Phys. Chem., 99, 6286, 1995.
"Resonance Raman and Time-Resolved Resonance Raman Studies of Complexes of Divalent Ruthenium with Bipyridine and 4,4'-Bipyrimidine Ligands," D. Manuel, D.P. Strommen, A. Bhuiyan, M. Sykora, J.R. Kincaid, J. Raman Spectroscopy, 28, 933, 1997.
"The Acid-Catalyzed Conversion of 1,3,5-Trimethyl-2,4,6-tris(2-Pyridyl)hexahydro-2-Triazine into the Asymmetric Monomer, N-Methylpyridine-2-carboxaldimine," A. Vasylyev, L.W. Castle, D.P. Strommen, Vibrational Spectroscopy, 20, 173-177, 1999.
"Ab initio and Density Functional Study of the Geometrical, Electronic and Vibrational Properties of 2,2'-bipyridine," L. Ould-Moussa, M. Castella-Ventura, E. Kassab, O. Poizat, D.P. Strommen, J.R. Kincaid, J. Raman Spectroscopy, 31, 377-390, 2000.
"Theoretical and Spectroscopic Characterization of 1,4-Bisethoxymethylene-(2,3)-butadione: A Molecule With an Extraordinarily Low (C=O) Stretching Frequency [1582cm-1]." K. Zborowski, D. Manuel, D.P. Strommen, L.M. Proniewicz, Vibrational Spectroscopy, 25, 7-17, 2001.
"Resonance Raman Spectra and Photophysical Properties of Ruthenium Complexes with the 3,3' Bipyridazine Ligand," J.S. Gardner, D.P. Strommen, W.S. Szulbinski, H. Su, J.R. Kincaid, J. Phys. Chem. A., 107, 351-357, 2003.