Role of intramolecular dynamics on intermolecular coupling in cyanine dye

Using pump-probe spectroscopy with sub-10-fs time resolution, we have studied coherent vibrational dynamics in a cyanine dye, in both monomeric and J -aggregate form. We show that coherent excitation of a particular intramolecular vibrational mode can result in a periodic modulation of the intermolecular excitonic coupling within the aggregate. This effect is manifested by a pronounced time-dependent modulation of the electronic transition energy of the aggregate. Such process may have direct importance in a range of electronic processes in supramolecular assemblies. © 2010 The American Physical Society.