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How fast is excitation energy transfer in the photosystem II reaction center in the low temperature limit? Hole burning vs photon echo

机译:在低温极限下,光能II反应中心中的激发能传输速度有多快?空穴燃烧与光子回波

摘要

The Qy(S1) excitonic structure, excitation energy transfer (EET), and primary charge-transfer separation processes of the isolated photosystem II reaction center (PS II RC) have proven to be formidable problems due, in part, to the severe spectral congestion of the So → Qy absorption spectrum. Recently, Prokhorenko and Holzwarth (J. Phys. Chem. B 2000, 104, 11563) reported interesting femtosecond 2-pulse photon echo data on the RC at 1.3 K for excitation wavelengths between 676 and 686 nm. At times longer than ∼1 ps and λ ≳ 678 nm, the echo decay curves are highly dispersive, which was attributed to a distribution of primary charge separation rates ranging from 2 ps to several hundred ps. A prompt subpicosecond component of the echo decay curves was also observed and suggested to be due to EET occurring in ∼100-200 fs. We present here persistent nonphotochemical hole burned spectra and transient triplet bottleneck hole spectra obtained with burn wavelengths between 680 and 686 nm, which show that the EET time in that wavelength region is no shorter than ∼5-10 ps. It is argued that the prompt component of the echo decay curves is due to relaxation of low-frequency phonons excited by the pump pulse. The argument is based on hole burning spectroscopy being the frequency domain equivalent of 2-photon echo spectroscopy, as well as on published photon echo data for chromophores in amorphous hosts.
机译:隔离光系统II反应中心(PS II RC)的Qy(S1)激子结构,激发能转移(EET)和一次电荷转移分离过程已被证明是一个严重的问题,部分原因是严重的光谱拥塞So→Qy吸收光谱最近,Prokhorenko和Holzwarth(J. Phys。Chem。B 2000,104,11563)报告了在676和686 nm之间的激发波长下,在1.3 K时RC上有趣的飞秒2脉冲光子回波数据。在比〜1 ps和λ678 nm更长的时间,回波衰减曲线是高度分散的,这归因于一次电荷分离率的分布范围从2 ps到几百ps。回波衰减曲线的瞬态亚皮秒分量也被观察到,并暗示是由于EET在约100-200 fs内发生的。我们在这里展示了持久的非光化学空穴燃烧光谱和在680至686 nm的燃烧波长下获得的瞬态三重态瓶颈光谱,表明该波长区域的EET时间不短于〜5-10 ps。有人认为,回波衰减曲线的迅速成分是由于泵浦脉冲激发的低频声子的弛豫所致。该论据是基于空穴燃烧光谱法(等效于2光子回波光谱法的频域),以及公开的无定形主体中发色团的光子回波数据。

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