Energy transfer in light-harvesting systems: implicatións of structural adaptatións, quantum coherence and correlatións

Abstract

Natural photosynthetic organisms have evolved a highly efficient and robust machinery to convert sunlight into useful chemical energy. Understanding the underlying principies behind such effective process is of fundamental scientific and technological interest. The research presented in this thesis has been motivated by recent experimental breakthroughs providing new insights into the supramolecular organization of the photosynthetic apparatus in purple bacteria and the mechanisms of energy transfer in light-harvesting components, particularly the evidence oflong-lasting coherent energy transfer in antenna proteins isolated from sorne bacteria and algae. The main objective of the research is to investigate both the functional consequences of the supramolecular arrangement of photosynthetic complexes and the role of quantum coherence and correlations in the quantum efficiency of lightharvestingsystems. This thesis addresses these two issues separately in two differentspatial scales. First, it examines the energy transfer dynamics in light-adapted photosynthetic membranes of purple bacteria, containing several photosynthetic comiii plexes. It presents and applies a novel approach to study energy transfer under continuous illumination, providing an insight into the role of light-adaptations inpurple bacteria. Second, it investigates the role of quantum coherence and correlations within a single photosynthetic complex. It shows that the interplay between correlations and coherent and decoherent dynamics provides photosynthetic complexes a non-trivial mechanism to optimize and control energy transfer efficiencies.It also discusses possible functional consequences of entanglement among pigments, with a focus on how long-lived quantum correlations are distributed among pigments and how this distribution relates to energy transfer efficiency. In general, this thesis gives insights into the structure-function relation in natural photosynthetic systems by highlighting relations between structural optimization and efficiency and by showing that the interference effects of quantum mechanics can equip natural organisms with an efficiency control mechanism they could not otherwise achieve.