Energy transfer in a newly synthesized coumarin-tetraphenylporphyrin donor-acceptor system was studied by time- and frequency-resolved fluorescence spectroscopy. The energy transfer kinetics was shown to be fast (transfer time ca. 500 fs) and efficient (quantum yield ca. 97%). The influence of interactions between excitations on the energy transfer dynamics was studied by intensity-dependent experiments. Although annihilation of excitations occurs for high irradiation doses, this does not affect the observed fluorescence transients. A kinetic model was constructed to explain these findings. Both the difference between the rate constants of energy transfer to singly and doubly excited acceptor states and the rate of radiationless decay from such doubly excited states were shown to be key parameters in the explanation of the intensity-dependent effects.