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Wave-packet Dynamics of Herzberg-Teller-type in Porphyrin J-aggregates Studied by Sub-5-fs Spectroscopy
Takayoshi Kobayashi and Hideaki Kano

Multi-channel sub-5-fs real-time spectroscopy was applied to molecular J-aggregates to shed light on the exciton-vibration coupling in the one-dimensional Frenkel exciton system, which shows small exciton-vibration interaction manifested by small Stokes shift of the fluorescence. The coherent molecular vibration with a 274 ± 44 cm-1 frequency is observed in the time-frequency two-dimensional difference absorption spectrum. The phase and amplitude of the oscillation has been analyzed to reveal that both of the negative (bleaching and photo-induced emission) and positive (photo-induced absorption) signals are modulated synchronously. The experimental result is well explained in terms of a transition dipole moment modulated by a dynamic intensity borrowing from an intense Soret-band (B-band) transition to a weak Q-transition through the vibronic interaction. The wave packet observed in the present study can be classified as a Herzberg-Teller type in contrast with the conventional Franck-Condon type frequently studied in relation with wave-packet control experiments.

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