Computer Simulation on Kinetics of Primary Processes in Photosynthesis Ⅰ——Mechanism of Exciton Annihilation of Excited State Decay in Phycobiliproteins

A discrete model was used for studying the effects of exciton annihilation on the decay behavior of the excited state in phycobiliprotein super-molecules. The simulation shows: The more the chromophores are and the higher the excitation beam intensity is, the more susceptible to annihilation is a system; annihilation starts to occur at 10~(13) photons/cm~2 and becomes saturated at about 10~(15)—10~(16) photons/cm~2 with the parameters used in the current work. Whether the exciton annihilation occurs or not should not be simply judged from whether the decaying data could be fitted with a mono-exponential function. The quantum yield of fluorescence decreases synchronously with the increase of exciton annihilation extent. The so called "safety intensity" has significance only in special cases. In fact, annihilation extent is dependent not only on the pulse intensity but also on the width of the pulse, the optical cross section of a chromophore as well as the light absorption coefficient of a system.