Abstract to TCD conference

Triplet-triplet energy transfer in light-harvesting complex II of purple bacteria: ab-initio calculation for the energy transfer matrix element by fragment spin difference method

Photoprotective function prevents the photosynthetic apparatus from damages by highly reactive singlet oxygen. Little is known on the theoretical basis of the photoprotection processes involving triplet states of the chromophores in photosynthesis. Theoretical estimate of the triplet-triplet energy transfer matrix element provides an important clue to the understanding of photoprotective function. Recently, we have developed the fragment spin difference (FSD) method which allow us to estimate the electronic coupling for many systems. In this presentation, we first compare the FSD results with our previous data [1] derived from other methods. We then apply the FSD method to the calculation of the electronic coupling between pigments in light-harvesting complex II of purple bacteria. The ab-initio coupling values are larger than previous semi-empirical values by one order magnitude. We will discuss the implication of these new coupling values in their possible role of avoiding singlet oxygen formation.