Ultrafast Energy-Transfer Pathway in a Purple-Bacterial Photosynthetic Core Antenna, as Revealed by Femtosecond Time-Resolved Spectroscopy
Ultrafast Energy-Transfer Pathway in a Purple-Bacterial Photosynthetic Core Antenna, as Revealed by Femtosecond Time-Resolved Spectroscopy
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DOI：
10.1002/anie.201003771
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发表时间：
2011-01-01
影响因子：
16.6
通讯作者：
Hashimoto, Hideki
中科院分区：
文献类型：
--
作者：
Kosumi, Daisuke;Maruta, Satoshi;Hashimoto, Hideki
紫色细菌的光合作用装置被设计为吸收光能，用于跨膜电荷分离。[1，2]在光收集的初级阶段，与捕光天线复合体结合的类胡萝卜素(CAR)吸收光谱中蓝色和绿色区域的阳光，并将这种激发能量传递给附近的细菌叶绿素(BCHL)。这个过程包括从CAR到BCHL的单重态-单重态激发-能量转移。有趣的是，尽管BCHL在能量上可能将激发能传递给CAR，但从BCHL到CAR的反向单线态EET不被认为是一种活性途径(图1)。在S0基态，如果CAR的线性多烯主链具有C2H点群对称性，则CAR表现出银对称性。由于最低单重态激发态S1(21Ag±)是单光子光学禁止态，因此S2(11Bu+)态是光学允许的最低单光子态。[3]在可见光-红外区，由于π！π*跃迁，bchl有两个明显的吸收带；[4]CAR在溶液中的超快光谱测量表明，从S2到S1和从S1到S0的内转换(IC)分别发生在大约100fs和几皮秒内。[2，5-7]稳态荧光激发和飞秒动力学测量已被用来估计光合作用系统的EET效率，报道的值从30%到近100%。[2]在紫细菌捕光复合体中，超快光谱测量表明单线态EET涉及S2！QX和S1！[2]单线态-单线态从叶绿素(Chl)的Qy到Car的S1是Frank假设的
The photosynthetic apparatus of purple bacteria is designed to absorb light energy, which is used to power transmembrane charge separation.[1, 2] In the primary stages of light harvesting, carotenoids (Car) bound to light-harvesting antenna complexes absorb sunlight in blue and green regions of the spectrum and transfer this excitation energy to nearby bacteriochlorophyll (Bchl). This process involves singlet–singlet excitation-energy transfer (EET) from Car to Bchl. Interestingly, even though it is energetically possible for Bchl to transfer excitation energy to Car, reverse singlet–singlet EET from Bchl to Car is not considered to be an active pathway (Figure 1).In the S0 ground state, Car displays Ag À symmetry if its linear polyene backbone has C2h point-group symmetry. Since the lowest singlet excited state, S1 (21Ag À), is one-photon optically forbidden, the S2 (11Bu+) state is the lowest onephoton optically allowed state.[3] Bchl has two distinct absorption bands due to π! π* transitions in the visible–infrared region; the bands are designated as the Qx and Qy bands.[4] Ultrafast spectroscopic measurements of Car in solution have revealed that the internal conversion (IC) from S2 to S1 and S1 to S0 occurs in approximately 100 fs and a few picoseconds, respectively.[2, 5–7] Steady-state fluorescence excitation and femtosecond kinetic measurements have been used to estimate EET efficiency in photosynthetic systems, with reported values ranging from 30 to nearly 100%.[2] In purplebacterial light-harvesting complexes, ultrafast spectroscopic measurements have shown that singlet–singlet EET involves the pathways S2! Qx and S1! Qy.[2] Singlet–singlet EET from Qy of chlorophyll (Chl) to S1 of Car was postulated by Frank