A few billion years ago photosynthetic bacteria developed the process of photosynthesis, allowing them to capture the energy of the sun for driving processes of life. Photosynthesis occurs in a complex set of membrane-bound proteins, in which solar photons are absorbed by a light-harvesting ‘antenna’, and the electronic excitation is transferred, within a few tens of picoseconds, to a reaction center, where it drives a charge separation that ultimately leads to the formation of a trans-membrane electrochemical potential. Recently atomic structures have been obtained for the most important photosynthetic reaction center and antenna complexes. The research focus of Biophysics is to display the time-evolution of the system down to the femtosecond time range, by employing ultrafast laser pulses to monitor fast absorption changes in the visible or infrared parts of the spectrum (pump-probe), or to monitor fast fluorescence transients (see figure below), and to develop physical models for the elementary events. Major research topics concern the mechanism of charge separation in photosynthetic reaction centers, specifically how the charge separation process is initiated. A second major research theme concerns the process of excitation energy transfer in the antenna complexes, with a focus on the dynamic interplay between the various proteins.
Time-resolved fluorescence of three types of light-harvesting proteins obtained from ironstarved
cyanobacteria (IsiA) and green plants (LHCII trimer and aggregate), measured with a streak camera set-up. This set-up allows a simultaneous recording of the decay (with a time-resolution of about 3 ps, vertical axis) and wavelength (horizontal axis). The data indicate a much faster decay of the fluorescence in the IsiA aggregate than in the LHCII complexes.