Abstract
The transfer of electronic charge in the reaction center of Photosystem II is one of the key building blocks of the conversion of sunlight energy into chemical energy within the cascade of the photosynthetic reactions. Since the charge transfer dynamics is mixed with the energy transfer dynamics, an effective tool for the direct resolution of charge separation in the reaction center is still missing. Here, we use experimental two-dimensional optical photon echo spectroscopy in combination with the theoretical calculation to resolve its signature. A global fitting analysis allows us to clearly and directly identify a decay pathway associated to the primary charge separation. In particular, it can be distinguished from regular energy transfer and occurs on a time scale of 1.5 ps under ambient conditions. This technique provides a general tool to identify charge separation signatures from the energy transport in two-dimensional optical spectroscopy.
Highlights
Evolving complex) has been studied by transient absorption spectroscopy and compared to the kinetics of the isolated D1/D2-cytb[559] PSII reaction center[7]
The details of the experimental setup, the sample preparation, and the measuring conditions are described in the Methods Section
To obtain a dynamical modeling of the CS, we have used a tight-binding model and show the theoretical results for the 2D spectra in the right column of Fig. 1(c) for the same waiting times. Both results agree well, which demonstrates the validity of our theoretical model
Summary
Revealed by a Global Analysis of Received: 29 March 2017 Accepted: 12 September 2017 Published: xx xx xxxx the Two-dimensional Electronic Spectra. A global fitting analysis allows us to clearly and directly identify a decay pathway associated to the primary charge separation It can be distinguished from regular energy transfer and occurs on a time scale of 1.5 ps under ambient conditions. The explicit use of a two pulse excitation sequence enables the identification of the inhomogeneous site distribution It allows for a direct tracking of the energy and charge transfer pathway and the coherent transfer dynamics as a function of absorption and emission spectra[10]. It was suggested that the CS processes are strongly related to these long-lived quantum oscillations, especially when the frequency of these coherent oscillations is resonant with the excitonic energy gap[17] Despite this significant progress of understanding CS in reaction center, direct evidence for the kinetics of CS in the PSII reaction center under ambient condition is still missing. We show that this feature can be straightforwardly understood already on the basis of a dimer model
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