UNDERSTANDING THE CHEMICAL REACTIVITY OF PHOTOEXCITED MOLECULES

Peter J. Wagner

University Distinguished Professor (b. 1938). B.A., 1960, Loyola University; Ph.D., 1963, Columbia University. NSF Postdoctoral Fellow, 1964, California Institute of Technology; NSF Senior Postdoctoral Fellow, 1971, UCLA; Guggenheim Fellow, 1983, National Research Council of Canada. Organic, physical and inorganic photochemistry.

517-355-9715, Ext. 132

wagnerp@msu.edu

Ancient man (not just modern Californians) worshipped the sun, recognizing it as the source of the energy required for life on Earth. The closest healthy modern equivalent to sun worship is the science of photochemistry, the subfield of chemistry that studies the chemical changes caused by light. My interests are primarily mechanistic; my students and I have helped define the basic factors that govern how light produces chemical change. To this end we perform a blend of synthesis, product analysis, kinetics, spectroscopy, and computations.

Because of the wide range of chemical and spectroscopic techniques used in photochemical research and because of its wide importance in biology, medicine, imaging technology, and synthetic chemistry, photochemistry provides especially broad research training for graduate students. Our current major interests are: 1) energy hopping between functional groups in polyfunctional molecules;

2) temperature and conformational effects on the reactivity of both photoexcited molecules and biradical intermediates formed from them, as in the example above; 3) radical cleavage of benzene–halogen bonds; and 4) the rearrangements that follow cycloadditions of double bonds to excited benzenes. This last process, shown below, exemplifies how some amazing transformations and high energy products can be induced by light. Note that the final product is a single stereoisomer when several could have been possible. Selective formation of single isomers is the most sought-after goal in synthetic organic chemistry.

We do a lot of NMR spectroscopy on our products in order to determine their exact structures and stereochemistries. We also analyze reactions by NMR in the many cases where products are sensitive to heat and acid or base catalysts. A unique advantage of photochemistry is that reactions can be performed at any temperature in totally neutral media, so as to avoid thermal or catalytic destruction of high energy products.

Representative Publications

Intramolecular Triplet Energy Transfer in Flexible Molecules: Electronic, Dynamic, and Structural Aspects, P. J. Wagner and P. Klan, J. Am. Chem. Soc., 121, 9625 (1999).

The Photochemistry of o-Benzylbenzophenone: a Pericyclic Cornucopia, M. Sobczak and P. J. Wagner, Tetrahedron Lett., 39, 2523 (1998).

How Many o-Xylylenols Can a Triplet o-Alkylphenyl Ketone Form?, P. J. Wagner, M. Sobczak, and B. Park, J. Am. Chem. Soc., 120, 2488 (1998).

Conformational Control of Product Ratios from Triplet 1,5-Biradicals, A. Zand, B. Park, and P. J. Wagner, J. Org. Chem., 62, 2326 (1997).

Photocyclization to Cyclopropanols and Exciplex Emission of b-Arylpropiophenones, W. Weigel and P. J. Wagner, J. Am. Chem. Soc., 118, 12858 (1996).