Excited State Localization and Delocalization of Internal Charge Transfer in Branched Push−Pull Chromophores Studied by Single-Molecule Spectroscopy

Single-molecule (SM) spectroscopy has been conducted to study exciton-like intramolecular charge transfer (ICT) coupling dynamics in two model dendritic systems containing branched ICT interactions. The strong coupling and stepwise photobleaching of the ICT branches in the dendrimers, which depend on the torsional disorder, have been demonstrated at the SM level. The fluorescence from the delocalized ICT excited state over two branches in push-pull molecules, which cannot be distinguished by means of conventional experiments probing the average behavior of large ensembles of molecules, has been observed at the SM level.