Dynamics of Photoinduced Charge Transfer and Hole Transport in Synthetic DNA Hairpins

Frederick D. Lewis was born in Boston, MA. He received his B.A. degree from Amherst College in 1965 and his Ph.D. from the University of Rochester in 1968. Following a postdoctoral appointment at Columbia University with N. J. Turro, he joined the faculty of Northwestern University in 1969. He is currently serving as President of the Inter-American Photochemical Society. His research interests are focused on the relation between photochemical behavior and molecular structure in systems ranging from small molecules to DNA.

Robert L. Letsinger was born in Bloomfield, IN. He received his B.S. degree in 1943 and his Ph.D. in 1945, both from MIT. He joined the faculty of Northwestern University in 1946 and is currently Clare Hamilton Hall Professor, Emeritus. He is best known for his pioneering studies in solid-phase synthesis and nucleic acid chemistry. His achievements have been recognized by election to the Nation Academy of Sciences and numerous awards, including the American Chemical Society A. C. Cope Scholar Award. His current interests include nanotechnology and its applications to DNA diagnostics.

Michael R. Wasielewski was born in Chicago, IL. He received his B.S. degree in 1971 and his Ph.D. in 1975, both from the University of Chicago. Following postdoctoral studies with R. Breslow at Columbia, he joined the scientific staff of the Chemistry Division of the Argonne National Laboratory. In 1994 he joined the faculty of Northwestern University, where he is Professor of Chemistry. He held a joint appointment at Argonne until 1999, when all of his research activities moved to Northwestern. His research focuses on electron-transfer reactions, the synthesis of donor−acceptor molecules and materials, ultrafast photophysical and photochemical processes in organic molecules and optoelectronic materials, magnetic properties of radical ion pairs, and the primary events of photosynthesis.

The dynamics of photoinduced charge separation and charge recombination processes in synthetic DNA hairpins have been investigated by means of femtosecond transient absorption spectroscopy. The driving force and distance dependence of charge-transfer processes involving singlet acceptors and nucleobase donors are consistent with a single-step superexchange mechanism in which the electronic coupling between the donor and acceptor is strongly distance dependent. The dynamics of reversible hole transport between a primary guanine donor and nearby GG or GGG sequences has also been determined and establishes that these sequences are very shallow hole traps.