Manoop Chenchiliyan will defend his doctoral thesis titled "Nano-structural Constraints for the Picosecond Excitation Energy Migration and Trapping in Photosynthetic Membranes of Bacteria" on 27. January 2017 at 15.15 at W. Ostwaldi 1, room B103.
prof Arvi Freiberg, Institute of Physics, University of Tartu
dr Esa Tyystjärvi, Turku University, Finland
Photosynthesis is a remarkable biological process through which light energy is converted into chemical energy by plants, algae, and some bacteria that nourishes nearly all life on earth, as we know it to date. The annual rate of energy captured by photosynthesis is approximately six times larger than the energy consumption by the entire mankind. Yet the sunlight-to-biomass conversion efficiency of photosynthesis is low, typically 0.1% in wild plants and 1-2% in advanced crop plants. Therefore, before we can harness the enormous potential of solar energy towards the global energy needs by developing highly efficient artificial, molecular-based technologies, one requires learning thoroughly how natural photosynthesis works. Recent advances in atomic force microscopy combined with innovative synthetic biochemistry have provided evidence for nanoscale structural adaptation of photosynthetic membranes in response to changing their habitats. This thesis deals with the effects of such nanoscale structural constraints on the ultrafast solar excitation energy migration and utilization in photosynthetic membranes of purple bacteria. Studying these complicated physical processes in bacteria is a lot easier than in plants or algae, because of their much simpler structure and the richer options of controlled genetic manipulations of the samples. In the present work, the multiple factors that govern the transfer and trapping rates of distinct quantum excitations called exciton polarons were identified and studied in bacterial photosynthetic membranes by picosecond time-resolved fluorescence spectroscopy. A consistent understanding of the underlying physical mechanisms was obtained by computer modelling. The results proved the robustness of the photosynthetic apparatus that functions surprisingly effectively under a wide variety of conditions. Even more unexpected was the discovery that special arrangements of the membrane pigment-protein components are able to significantly enhance the efficiency of solar energy harvesting.