Primary Processes and Structure of the Photosystem II Reaction Center. 3. Kinetic Analysis of Picosecond Energy Transfer and Charge Separation Processes in the D1-D2-cyt-b559 Complex Measured by Time-Resolved Fluorescence†

An extensive picosecond fluorescence study has been performed on isolated D1-D2 reaction centers (RCs) from photosystem (PS) II at room temperature as a function of excitation and emission wavelength with a time resolution of about 2 ps. The study comprizes more than 50 excitation/emission wavelength pairs. Global analysis for individual excitation wavelengths and, alternatively, for the entire excitation/emission wavelength matrix has been performed. These analyses show that over a time range of 2 ns five exponentials are required to adequately describe the data. The shortest lifetime component, whose amplitude dominates the excited state decay for excitation in the red part of the absorption spectrum, is ≈3 ps. Further lifetime components fall into the 6-12, 20-30, and 60-130 ps and the several nanosecond ranges. In the combined global analysis at least five lifetime components (400 ps fit window), again with ≈3 ps as the shortest one (again dominant in amplitude for long excitation wavelengths), and most likely even six components are required to describe the data. The dominance and necessity of the ≈3 ps component is demonstrated also by exhaustive search error analysis on the data in the global mode. Kinetic target analysis on models of various complexity has been performed, again on data sets from individual excitation wavelengths and on the combined data set. Such analyses have been performed for the first time for the D1-D2 kinetics, and they allow an assignment of the origin of the various lifetime components. The target analyses yielded realistic species