UD Lab

The goal of our research is to elucidate microscopic dynamics of prompt chemical and photophysical processes in condensed phases. We put particular emphasis on the initial stages of the processes and the coupling between the electron and nuclear degrees of freedom, where the nuclear coordinates include both inter- and intra-molecular, as they play critical roles in most of the spectroscopy and determine the fate of a photoexcited system. Our primary research tool is the femtosecond time-domain spectroscopy that can determine the structure and energy levels of a molecule directly while a molecule is undergoing chemical reactions and physical processes. Depending on the system under scrutiny, a variety of femtosecond techniques including those developed in our own laboratory are employed; time-resolved fluorescence (TRF), 3 pulse photon echo peak shifts (3PEPS), spectrally resolved four wave mixing (SRFWM), transient grating (TG), tau-resolved transient grating (TRTG), and transient absorption (TA). Summarized below are some of our recent results made possible by the state-of-the-art instruments developed in our laboratory. When a molecule is excited impulsively by a short pulse of light, vibrational wave packets are created, which are manifested in the oscillations of the time trace in various time-resolved spectroscopies, TA being a typical example. The nature of the vibrational modes excited and their dynamics provide a wealth of information on the molecular dynamics, structures of the states involved, and the coupling between them. In general, the coherent nuclear wave packet can be launched by any nuclear rearrangements occurring faster than roughly half of the vibrational period. Excited state intramolecular proton transfer (ESIPT) is one such example. Observation o