Coherent Nuclear Wave Packets Generated by Ultrafast Intramolecular Charge-Transfer Reaction

Intramolecular charge-transfer (ICT) dynamics, including reaction coordinates, structural changes, and reaction rate, has been noted experimentally and theoretically. Here we report the ICT dynamics of laurdan investigated by time-resolved fluorescence at extreme time resolution of 30 fs. A single high-frequency coherent nuclear wave-packet motion on the product potential surface is observed through the modulation of the fluorescence intensity in time. Theory and experiment show that this vibrational mode involves large displacement of the carbon atoms in the naphthalene backbone, which indicates that the naphthalene backbone coordinates are strongly coupled to the ICT reaction of laurdan, not the twisting or planarization of the dimethylamino group.