Abstract

Non-Adiabatic Excited-State Molecular Dynamics simulations (NA-ESMD) and Excited- State Instantaneous Normal Modes (ES-INMs) analyses have been applied to study the nature of the electronic and vibrational energy transfer in different model dendritic molecules built from linear poly-phenylene ethynylene (PPE) units linked: The initial laser excitation creates an exciton delocalized between the absorbing two-ring linear PPE units. Thereafter, we observe an ultrafast directional change in the spatial localization of the transient electronic transition density. The analysis of the intramolecular flux of the transition density shows a sequential through-bond two-ring→three-ring→fourring transfer as well as an effective through-space direct two-to-four ring transfer. The vibrational excitations of C(triple-bond)C stretching motions change according to that. A mechanism of unidirectional energy transfer is presented based on the variation of the energy gaps between consecutive electronic excited states in response to the intramolecular flux of the transition density. Finally, we describe the state-specific vibrations that participate in the unidirectional energy transfer between the coupled chromophores in a branched dendrimeric molecule.

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