Big Lessons from Small Bacteria : Following Photo-driven Processes in Photosynthetic Systems with Multidimensional Spectroscopy

Sammanfattning: Sunlight is a plentiful, continuously flowing source of energy, fuelling life on Earth as we know it. To use this potential, plants, cyanobacteria and photosynthetic bacteria evolved to absorb solar radiance and convert it into a chemically stable form by performing a process known as photosynthesis. Despite a wide variety of photosynthetic systems, the initial steps of photosynthesis are similar. They involve the absorption of photons by light-harvesting antennas, transferring this energy to photosynthetic reaction centres and primary charge separation.Over the recent decades, scientists put much effort into understanding the driving forces behind the photosynthetic processes. Exploring bacterial photosynthesis became a field of its own due to their high robustness towards living conditions and efficient energy transfer and trapping within photosynthetic units. However, sizes in the nanometre scale, high pigment densities and congested absorption spectra, energy and electron transfer rates from hundreds of femtoseconds to tens of picoseconds made the primary steps of bacterial photosynthesis challenging to follow and explore.This thesis presents studies of photo-driven processes inside various photosynthetic systems using two-dimensional electronic spectroscopy, an advanced technique combining high temporal and spectral resolutions and well suited for studying excitation-induced processes within photo-active systems. The first chapter of this thesis introduces the main photosynthetic systems under investigation: chlorophyll-type molecules, bacterial reaction centres and photosynthetic units of the purple bacterium Rhodobacter sphaeroides and the green bacterium Chloroflexus aurantiacus. The second chapter delivers a detailed introduction to the main experimental technique – two-dimensionalelectronic spectroscopy – and provides background on following and understanding recorded signals.The results chapter of this thesis summarises observations of vibronic coupling inside chlorophyll c1 molecule. In addition, it presents energy and electron transfer dynamics within the bacterial reaction centres from the purple bacterium Rhodobacter sphaeroides and the green bacterium Chloroflexus aurantiacus and describes means to identify precursor states for charge transfer in (most probably every) reaction centre. Final results present mapping excitation energy transfer and trapping processes inside intact living cells of the green bacterium Chloroflexus aurantiacus. The thesis finishes with concluding remarks and some future directions.