Excited states of pigments in photosystem II reaction centers of photosynthesis: Characterization into a central dimer and remaining monomers

In the reaction center (RC) of Photosystem II in photosynthesis, neighboring pigments are nearly equidistantly separated at 8-10 A center-to-center. This fact has let many people consider that excited states in the pigment assembly therein may be multimers covering more than four pigments. In reality, however, the excited states are dimeric on the central pair (P) of chlorophylls, while monomeric on other pigments. Such characterization was derived from their energy broadening which was obtained by fitting the absorption spectrum of RC, based on recent mutagenesis studies clarifying that P* is not lowest in RC differently from other photosystems.