Energy transfer from Förster-Dexter theory to quantum coherent light-harvesting

Electronic excitation energy transfer is ubiquitous in a variety of multi- chromophoric systems and has been a subject of numerous investigations in the last century. Recently, sophisticated experimental and theoretical studies of excited state dynamics have been developed with the purpose of attaining a more detailed picture of the coherent and incoherent quantum dynamics relevant to energy transfer processes in a variety of molecular aggregates. In particular, great efforts have been made towards finding experimental signatures of coherent superpositions of electronic states in some light-harvesting antenna complexes and to understand their practical implications. This review intends to provide some foundations, and perhaps inspirations, of new directions of research. In particular, we emphasise current opinions of several effects that go beyond normal Förster theory and highlight open problems in the description of energy transfer beyond standard approximations as well as the need of new approaches to characterise the 'quantumness' of excited states and energy transfer dynamics in multichromophoric systems.