Abstract

The crucial step in the conversion of solar energy to chemical energy in Photosynthesis is the separation of charges by the reaction center. However, the fundamental mechanism responsible for the near unity quantum efficiency of this process is unknown. Here we elucidate the role of coherence in determining the efficiency of charge separation in the plant photosystem II reaction centre (PSII RC) by comprehensively combining experiment (two-dimensional electronic spectroscopy) and theory (standard Redfield theory). We reveal the presence of electronic coherence between exciton and charge-separated states maintained by vibrational modes and demonstrate that electronic coherence promotes efficient and ultrafast charge separation. We conclude that the discovered coherent mechanism operational in PSII RC can be used to design artificial photosynthetic devices with nearly 100% photoconversion efficiency.