What Two-Dimensional Electronic Spectroscopy Can Tell Us about Energy Transfer in Dendrimers: Ab Initio Simulations.

Two-dimensional (2D) electronic spectra of the phenylene ethynylene dendrimer with 2-ring and 3-ring branches were evaluated by combining the on-the-fly trajectory surface hopping nonadiabatic dynamics and the doorway-window simulation protocol. The ground state bleach (GSB), stimulated emission (SE), and excited-state absorption (ESA) contributions to the 2D signal were obtained and carefully analyzed. The results demonstrate that the ultrafast intramolecular nonadiabatic excited-state energy transfer (EET) from the 2-ring to the 3-ring units is comprehensively characterized by the SE and ESA signals. It is proven that the monitoring of the 2D ESA signal is especially convenient, because it is spectrally well separated from the SE and GSB signals. Hence, 2D electronic spectroscopy provides a detailed and multifaceted view of the intramolecular EET process in dendrimers.