Department of Physics and Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1040, USA.
J Phys Chem A. 2013 Jan 10;117(1):34-41. doi: 10.1021/jp3081707. Epub 2012 Dec 20.
We report simulations of the two-dimensional electronic spectroscopy of the Q(y) band of the D1-D2-Cyt b559 photosystem II reaction center at 77 K. We base the simulations on an existing Hamiltonian that was derived by simultaneous fitting to a wide range of linear spectroscopic measurements and described within modified Redfield theory. The model obtains reasonable agreement with most aspects of the two-dimensional spectra, including the overall peak shapes and excited state absorption features. It does not reproduce the rapid equilibration from high energy to low energy excitonic states evident by a strong cross-peak below the diagonal. We explore modifications to the model to incorporate new structural data and improve agreement with the two-dimensional spectra. We find that strengthening the system-bath coupling and lowering the degree of disorder significantly improves agreement with the cross-peak feature, while lessening agreement with the relative diagonal/antidiagonal width of the 2D spectra. We conclude that two-dimensional electronic spectroscopy provides a sensitive test of excitonic models of the photosystem II reaction center and discuss avenues for further refinement of such models.
我们报告了在 77 K 下 D1-D2-Cyt b559 光系统 II 反应中心 Q(y) 带的二维电子光谱的模拟。我们的模拟基于一个现有的哈密顿量，该哈密顿量是通过同时拟合广泛的线性光谱测量值并在修正的 Redfield 理论中描述而得出的。该模型与二维光谱的大多数方面，包括整体峰值形状和激发态吸收特征，都取得了合理的一致。然而，它并没有再现从高能到低能激子态的快速平衡，这一点可以通过对角线下方的强交叉峰明显看出。我们探索了对模型的修改，以纳入新的结构数据并改善与二维光谱的一致性。我们发现，增强系统-浴耦合并降低无序度显著改善了与交叉峰特征的一致性，同时降低了与二维光谱的相对对角线/反对角线宽度的一致性。我们得出结论，二维电子光谱为光系统 II 反应中心的激子模型提供了一个敏感的测试，并讨论了进一步改进此类模型的途径。
