The Quest for Photosynthetic Excitons: My Pilgrimage

Arvi Freiberg
Institute of Physics & Institute of Molecular and Cell Biology, University of Tartu, W. Ostwald Str. 1, Tartu, Estonia

In photosynthesis solar photons are converted into molecular excitations in light-harvesting pigment-protein complexes and the absorbed energy is transported to the reaction center complexes, where further conversion into chemical energy occurs. The efficiency of light harvesting is significantly enhanced by the inter-pigment exciton interactions, which not only broaden the energy spectrum of the light-harvesting complexes, but also, by virtue of building up a suitable energetic ladder of exciton states, allows ultrafast excitation energy transfer with minimal losses. By nature, the photosynthetic excitons are localized exciton polarons rather than idealized Frenkel excitons, due to strong coupling to environmental phonons and significant conformational disorder characterizing the pigment-protein complexes.

Here, I present a personalized overview of the ideas and experiments toward this general conclusion. Current status of the field and the remaining challenges will also be discussed based on some fairly recent developments of experiment and theory.