Control of emission spectrum and excited state dynamics in a cyanine dye molecule with femtosecond chirped pulses

Summary form only given. Femtosecond wavepacket dynamics has been recently studied to realize the possibility of controlling molecular dynamics using tailored ultrashort pulses. Especially, an intrapulse pump-dump process and a selective excitation of vibrational wavepacket motion were demonstrated with chirp-controlled femtosecond pulses. At higher excitation density, the fluorescence spectrum was measured to monitor the excited-state dynamics, and the spectrum was claimed to be independent of the pulse chirp. In the present study, we could for the first time observe the dependence of emission spectrum and excited-state dynamics in cyanine dye molecules on the chirp rate of the pump pulse. The fluorescence spectrum is expected to be dependent on the chirp rate as a result of competition among the pump-dump configuration change associated with the vibrationally coupled modes, and vibration-vibration energy transfer. The chirp affects the branching ratio among these three processes, which can change the emission spectrum. The transient response of the excited state was also found to change drastically in a femtosecond pump-probe measurement. The dye molecule studied is 3,3´-diethylthiatricarbocyanine iodide.