IR spectrum and localization of excitation of reaction center of photosystem II in triplet state

Using the density functional theory, vibrations of different model forms of the chlorophyll a molecule in the ground and triplet states have been calculated. The assignment of the experimental difference IR spectrum corresponding to the formation of the triplet state of the photosynthetic reaction center of photosystem II has been proposed on this basis. It has been shown that molecules of accessory chlorophyll B _A and B _B located between the special pair and H _A and H _B pheophytin molecules can be involved in the intermolecular hydrogen bond with the water molecule. The energy of this interaction in the triplet state of molecules for B _A is larger on 6 kcal/mol. This allows us to relate this pigment to the location of the triplet excitation at the reaction center of photosystem II.