Intramolecular Förster energy transfer in a dendritic system at the single molecule level.

The photophysics of a dendrimer containing four donor chromophores and one acceptor chromophore are studied at the single-molecule level. Upon excitation of the donors exclusive acceptor emission is observed due to efficient Förster energy transfer. For 70% of the molecules donor emission is observed after bleaching of the acceptor, leading to a reduction of the Förster energy transfer efficiency. Furthermore, we demonstrate that in this molecular system the donor chromophores do not bleach by a triplet-sensitized photooxidation.