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September 3, 2008


Dr. Torsten Fiebig
Eugene F. Merket Chemistry Center
Boston College
"Photonics with Ultrafast Laser Pulses - from DNA to Semiconductor Nanorods"

Abstract.  To deepen our understanding of elementary molecular processes, i.e. energy, electron and proton transfer, we develop and apply ultrafast spectroscopic techniques to a variety of natural and artificial molecular materials.  For example, the interaction of UV-radiation with DNA on the ultrafast time scale raises the question of how electronic excess energy delocalizes and dissipates in p-stacked nucleic acids. Using femtosecond broadband pump-probe spectroscopy, we can trace the electronic excitation both in time and in space along the base stack in a series of single- and double-stranded DNA oligonucleotides. The obtained results demonstrate not only the presence of delocalized exciton states as a result of ultraviolet light absorption, but reveal also the spatial extent of the electronic delocalization.  The concept of molecular electron donor-acceptor dyades has recently been extended to semiconductor heterostructure nanorods where the optical charge transfer process is governed by quantum confinement. Femtosecond bleaching dynamics help to answer the important mechanistic questions that need to be addressed before these new materials can be used in photovoltaic devices for solar energy conversion. A presentation of emerging applications of ultrafast high-power IR pulses in biology and medicine will round off the presentation.

Vanderbilt University