Photochemical processes in photosynthesis studied by advanced electron paramagnetic resonance techniques *

Various continuous-wave and pulse electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) experiments performed on the radical species occurring in photosynthetic reaction centers of plants and bacteria during light-induced charge separation are reviewed here. Emphasis is placed on time-resolved experiments performed on short-lived intermediate states such as radical pairs and triplet states for which also hyperfine information can be obtained from pulse ENDOR spectroscopy. Detailed insight into the electronic structure of these intermediates and their interaction with the protein environment is now becoming available.