31. October 2014 at 15 in Physicums aud B103 will defend Mihkel Pajusalu his doctoral theses in physics "Localized Photosynthetic Excitons"
Prof. Arvi Freiberg, Institute of Physics, University of Tartu
Dr. Margus Rätsep, Institute of Physics, University of Tartu
Dr Leonas Valkunas, Vilnius University, Lithuania
Dr Georg Liidja, National Institute of Chemical Physics and Biophysics, Estonia
Virtually all of the food consumed by humans has been produced by capturing sunlight and storing it as chemical energy in the process of photosynthesis. Living nature manages to do this with very common chemical elements by placing them into complex arrangements on the scale of a few nanometres.
Purple bacteria are possibly the oldest organisms on the Earth capable of harvesting the sunlight to feed themselves. During billions of years, bacteria have developed very complex methods for energy capture that could also prove useful in human technology. The complexity in understanding these systems lies in the fact that their operation is based on quantum mechanical effects, which ordinarily exhibits in highly regular systems (such as semiconductor crystals) at extremely low temperatures, such as at the boiling point of liquid helium (-270 °C).
In this work we tried to expand our understanding of the mechanisms behind the light-harvesting complexes of purple bacteria. We managed to prove that these small nanostructures are capable of collecting solar photons and forming them into excitons that can then be transported and captured as chemical energy. This happens despite being far from the conditions present at near absolute zero temperature semiconductor crystals. For this, we used optical spectroscopy and quantum mechanical modelling. The model developed in this work also explains the microscopic differences between individual light-harvesting complexes, which have earlier caused misunderstanding and misinterpretation of experimental data from these complexes. This has led to a better understanding of the operation of these complexes and hopefully can be reverse-engineered in the future to manufacture biologically inspired light-harvesting systems for humanity’s energy needs.