Energy transfer and trapping in Photosystem II core particles with closed reaction centers

Picosecond absorbance changes in the Q_y absorption region were measured on Photosystem II core particles with closed reaction centers by the one-color pump-probe method. The induced absorption changes are well described by three components with lifetimes of 21 ± 6 ps, 80 to 200 ps and 1.5 ns, in addition to a non-decaying component. The 1.5 ns lifetime component is assigned to recombination of the primary radical pair in equilibrium with the excited state. Since the lifetime of the intermediate component depends on the excitation wavelength and its spectrum differs from that of the 21 ps component, a rapid equilibration of the excitations over the whole antenna is excluded. The 21 ps and the intermediate component are discussed in terms of energy transfer and trapping processes.