The excited exciton (S2-exciton originating from the second-excited state of the molecules) was studied by real-time spectroscopy with 30-fs pulses. The ultrafast dynamics due to the S2–S1 internal conversion process were clearly observed in the pump–probe signal. The signal was modulated by the coherent molecular vibrations with 241 ± 4 cm-1 and 319 ± 4 cm-1 frequencies. The phase of the oscillation indicates that not only the ground state but also the excited state contribute to the oscillatory signal. The excited-state wave-packet motion was explained by dynamic intensity borrowing mechanism from the S2 ⇄ S0-transitions to the S1 ⇄ S0-transitions.
2002 The Chemical Society of Japan