Biexciton resonance energy transfer in a model photosystem

The absorption of two photons by a concentrated assembly of identical chromophores can lead to formation of a biexciton. This work concerns the transfer of biexcitonic energy from a ring to a central donor, with a particular focus on rates and geometric effects. Quantum amplitudes are expressed in terms of orientation factors with a clear physical significance and detailed calculations are performed on an idealised, three-fold symmetric photosystem�a structural motif common in a variety of natural and artificial light-harvesting systems.