The primary processes of bacterial photosynthesis - Ultrafast reactions for the optimum use of light energy

Femtosecond spectroscopy is used to study the molecular mechanisms of the primary electron transfer. Data on native and mutated reaction centers of Rhodopseudomonas viridis show that primary electron transfer is an ultrafast stepwise reaction. The electron is transferred via a chain of pigments: In a first reaction step the electron is transported from the special pair to the accessory bacteriochlorophyll with a time constant of approximate to 3 ps. A second, faster reaction carries the electron with 0.65 ps to a bacteriopheophytin. Experiments on mutated reaction centers with strongly modified reaction times yield additional information on energetics, reorganisation energies and electronic coupling of the reaction center. A consistent theoretical treatment of the data shows that standard nonadiabatic theory describes well the primary electron transfer process. It also reveals that the realised reaction parameters optimise the reaction centers for highest possible quantum yield.