10.1021/bi1003926.s001 Elisabet Romero Elisabet Romero Ivo H. M. van Stokkum Ivo H. M. van Stokkum Vladimir I. Novoderezhkin Vladimir I. Novoderezhkin Jan P. Dekker Jan P. Dekker Rienk van Grondelle Rienk van Grondelle Two Different Charge Separation Pathways in Photosystem II American Chemical Society 2010 ultrafast charge separation Different Charge Separation Pathways trap states excitation conditions chemical energy target analysis 77 K charge separation excitation energy trap states PD 1PD 77 K absorption experiments reaction center complexes Photosystem IICharge separation protein motions causes charge separation pathways Photosystem II reaction center preparations ChlD 1PheD time scales 2010-05-25 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Two_Different_Charge_Separation_Pathways_in_Photosystem_II/2767129 Charge separation is an essential step in the conversion of solar energy into chemical energy in photosynthesis. To investigate this process, we performed transient absorption experiments at 77 K with various excitation conditions on the isolated Photosystem II reaction center preparations from spinach. The results have been analyzed by global and target analysis and demonstrate that at least two different excited states, (Chl<sub>D1</sub>Phe<sub>D1</sub>)* and (P<sub>D1</sub>P<sub>D2</sub>Chl<sub>D1</sub>)*, give rise to two different pathways for ultrafast charge separation. We propose that the disorder produced by slow protein motions causes energetic differentiation among reaction center complexes, leading to different charge separation pathways. Because of the low temperature, two excitation energy trap states are also present, generating charge-separated states on long time scales. We conclude that these slow trap states are the same as the excited states that lead to ultrafast charge separation, indicating that at 77 K charge separation can be either activation-less and fast or activated and slow.