A THEORETICAL STUDY OF EXCITONS IN CHLOROPHYLL a PHOTOSYSTEMS ON A PICOSECOND TIMESCALE

Abstract

Abstract— The creation and decay of singlet excitons in structurally‐explicit Chi a photosystems were investigated by numerical integration of the appropriate Master Equations. The antenna chlorophylls were excited by a simulated 6ps Gaussian light pulse. Positions and orientations for the antenna chlorophylls were randomly generated within regions whose size and shape were chosen to be appropriate for the particles observed in freeze‐fractured photosynthetic membranes. Among the variables considered were chlorophyll concentration, depth of the trap (i.e. P680 or P700), and the R 0 parameter for Förster transfer. Among the properties considered were antenna fluorescence lifetime; detrapping rates; the instantaneous and integrated quantum yields for antenna fluorescence and intersystem crossing; and the instantaneous and integrated quantum yields for trap fluorescence, intersystem crossing, and photochemistry. A variety of experimental evidence was used as input to the computational model.