Unified treatment of coherent and incoherent electronic energy transfer dynamics using classical electrodynamics

Recent experiments on resonance energy transfer (RET) in photosynthetic systems have found evidence of quantum coherence between the donor and the acceptor. Under these conditions, Fo?rster's theory of RET is no longer applicable and no theory of coherent RET advanced to date rivals the intuitive simplicity of Fo?rster's theory. Here, we develop a framework for understanding RET that is based on classical electrodynamics but still captures the essence of the quantum coherence between the molecules. Our theory requires only a knowledge of the complex polarizabilities of the two molecules participating in the transfer as well as the distance between them. We compare our results to quantum mechanical calculations and show that the results agree quantitatively.