Ultrafast transient dynamics of Zn(II) porphyrins: Observation of vibrational coherence by controlling chirp of femtosecond pulses

Femtosecond coherence spectroscopic study on porphyrin molecules has demonstrated that the oscillatory features residing at the transient absorption and fluorescence decay profiles are strongly correlated with the lifetimes of the excited states and the displacements of the minima of the potential energy surfaces that are involved in the pump and probe laser pulses. We have attained a greater degree of control in the wave packet dynamics in the transient absorption by controlling the chirp of the ultrashort optical pulses. This feature provides a clue to the excited potential energy surface such as its curvature and displacement. For two representative porphyrin monomers, Zn-II tetraphenylporphyrin and Zn-II octaethylporphyrin, we were able to obtain detailed information on the excited state dynamics and subsequent structural changes based on the comparison between the frequency spectra retrieved from the oscillatory features in the transient absorption and fluorescence temporal profiles and the ground state Raman spectra. (C) 2003 American Institute of Physics.