Cross-peak-specific two-dimensional electronic spectroscopy
Cross-peak-specific two-dimensional electronic spectroscopy
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DOI：
10.1073/pnas.0701201104
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发表时间：
2007-09-04
影响因子：
11.1
通讯作者：
Fleming, Graham R.
中科院分区：
文献类型：
--
作者：
Read, Elizabeth L.;Engel, Gregory S.;Fleming, Graham R.
分子间的电子耦合决定了分子聚集体系的光学性质。特别令人感兴趣的是光合色素蛋白质复合物，它吸收阳光，然后有效地将能量导向光合反应中心。二维（2D）超快光谱已被广泛地用于红外（IR），并且越来越多地用于可见光以探测激子耦合和观察动力学，但是耦合的非对角光谱特征经常被宽对角峰遮蔽，特别是在可见光区域。旋转激发样品的激光脉冲的偏振可以突出某些光谱特征，并且已经在IR中证明了使用偏振脉冲序列来阐明2D光谱中的交叉峰以用于振动跃迁。在这里，我们开发了二维电子光谱，使用交叉峰特定的脉冲偏振条件下的调查的芬娜-马修斯-奥尔森光收集复杂的绿色光合细菌。我们的测量成功地突出了2D光谱的非对角特征，并结合基于特定能级路径和理论模拟产生的特征的符号的分析，我们表征了负责光谱特征的主导响应路径。交叉峰特定的2D电子光谱提供了深入了解发色团间的耦合，以及到充满活力的途径产生的信号。利用飞秒分辨率，我们还观察到依赖于这些耦合和与蛋白质环境的相互作用的动力学过程。
Intermolecular electronic coupling dictates the optical properties of molecular aggregate systems. Of particular interest are photosynthetic pigment-protein complexes that absorb sunlight then efficiently direct energy toward the photosynthetic reaction center. Two-dimensional (2D) ultrafast spectroscopy has been used widely in the infrared (IR) and increasingly in the visible to probe excitonic couplings and observe dynamics, but the off-diagonal spectral signatures of coupling are often obscured by broad diagonal peaks, especially in the visible regime. Rotating the polarizations of the laser pulses exciting the sample can highlight certain spectral features, and the use of polarized pulse sequences to elucidate cross-peaks in 2D spectra has been demonstrated in the IR for vibrational transitions. Here we develop 2D electronic spectroscopy using cross-peak-specific pulse polarization conditions in an investigation of the Fenna-Matthews-Olson light harvesting complex from green photosynthetic bacteria. Our measurements successfully highlight off-diagonal features of the 2D spectra and, in combination with an analysis based on the signs of features arising from particular energy level pathways and theoretical simulation, we characterize the dominant response pathways responsible for the spectral features. Cross-peak-specific 2D electronic spectroscopy provides insight into the interchromophore couplings, as well as into the energetic pathways giving rise to the signal. With femtosecond resolution, we also observe dynamical processes that depend on these couplings and interactions with the protein environment.