Dynamics In Peripheral Light-Harvesting Of Photosynthesis

The photosynthesis is the most important and highest efficient photochemical process found in photosynthetic organisms in the nature. The process of photosynthesis origins in the capture of light energy, and energy is captured by the Reaction Center via ultrafast and high efficient transfer processes, all these processes which all take place in the tens picosecond or subpicosecond time region. The study on pathways and photophysical / photochemical mechanisms of ultrafast energy transfer has been attracted much attention from the experimental and theoretical scientists, and it is also an important subject of researchers from physics, chemistry and biology. In this thesis, we studied the photoinduced ultrafast dynamics taking place in peripheral light-harvesting complex LHCII from high plant, the peripheral light harvesting antenna LH2 from purple bacteria Rb. sphaeroides 601 (LH2-RS601) and it's mutation LH2-GM309 by using ultrafast spectroscopic techniques. The results obtained in our experiments can be concluded as follows,1. In the LHCII isolated from green plant, there exists ultrafast energy transfer processes between the electronic states of different chlorophylls (Chl a and Chl b) involved and also among the excitonic states of Chl a. It was observed from our femtosecond pump-probe experiments that the process of energy relaxation from Chl b to its neighboring Chl a in the monounit of LHCII takes place in 200~300 fs time region, which can be interpreted with the conventional Forster excitation transfer mechanism, on the other hand, the excitation relaxation between the excitonic states of Chl a is of subpicosecond time scale. In addition, the energy equilibrium process of intermo -lecular in Chl a was also observed which happens in several picoseconds.