Two-Dimensional Electronic Spectroscopy of the Photosystem II D1D2-cyt.b559 Reaction Center Complex.

[摘要] Two-dimensional electronic spectroscopy (2DES) is a powerful new technique for examining the electronic and vibronic couplings and dynamics of chemical, semiconductor, and biological samples. We present several technical innovations in theimplementation of 2DES. We have performed two-color 2DES experiments, extending the technique’s ability to study energy transfer to states at frequencies far from the initial absorption. We have demonstrated 2DES in the pump-probe geometry using a pulse-shaper. This method eliminates many technical challenges inherent to previousimplementations of 2DES, making it a more widely accessible technique. To broaden the available frequency information, we have demonstrated 2DES with a continuum probe pulse. We have utilized this method to observe vibrational wavepacket dynamics in a laser dye, demonstrating that these dynamics modulate 2D lineshapes andmust be accounted for in modelling 2DES data.We perform 2DES studies on the Qy band of the D1D2-cyt.b559 reaction center of plant photosystem II. This reaction center is the core oxygen-evolving complex in plant photosynthesis, taking in light energy and forming a charge separated state capable of splitting water. Understanding the relationship between the structure and function has both fundamental importance and applications to improving artificial light-harvesting. Traditional spectroscopy methods have been unable to completely resolve the time-ordering of energy and charge transfer events or the degree of electronic coupling between chromophores due to severe spectral congestion in the Qyband. 2DES extends previous methods by frequency-resolving an additional dimensionto reveal the degree of static disorder and electronic coupling, as well as a detailedpicture of energy and charge transfer dynamics that will allow tests of excitonic modelsof the reaction center. Our data show direct evidence of electronic coupling andrapid sub-ps energy transfer between ;;blue” and ;;red” states. We measure chargetransfer times of 1-3 ps, with evidence to support a recent model in which primarycharge separation follows two separate pathways. Slow time components of ~7 psand ~50 ps are also observed. The former is consistent with slow energy transfer from blue-absorbing states while the latter may indicate secondary charge transfer or slow charge transfer from a degenerate trap state.

[发布机构] University of Michigan

[效力级别] Two-dimensional Spectroscopy

[关键词] Ultrafast Spectroscopy;Two-dimensional Spectroscopy;Photosynthesis;Photosystem II;Physics;Science;Physics