Interexciton-state relaxation and exciton localization in allophycocyanin trimers
Interexciton-state relaxation and exciton localization in allophycocyanin trimers
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DOI：
10.1021/jp960454b
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发表时间：
1996-08-15
影响因子：
--
通讯作者：
Beck, WF
中科院分区：
文献类型：
--
作者：
Edington, MD;Riter, RE;Beck, WF
我们采用动态吸收，瞬态烧孔和离散双色泵浦探测飞秒光谱方法，以获得时间分辨的激子动力学的三聚体的别藻蓝蛋白，在蓝藻的藻胆体的核心的主要组成部分。别藻蓝蛋白三聚体含有藻蓝胆素（开链四吡咯）二聚体的C-3对称阵列。飞秒时间分辨的泵浦-探测光谱和单波长瞬变观察别藻蓝蛋白制剂进行了解释与一系列的计算光谱的帮助下，这是基于分配的基态吸收光谱的激子耦合的发色团二聚体。观察到的和计算的时间分辨泵浦探测光谱表明，激发态间弛豫，二聚体激子状态之间的辐射转移的人口，是负责的光谱红移类似于30-fs的时间尺度。的泵浦探测光谱的时间演化是不一致的，占基态吸收光谱的亚皮秒福斯特能量转移路径连接的非耦合的发色团对的模型。在一个较慢的时间尺度上，从300 fs到ps的延迟范围内延伸，时间分辨光谱演变的方式与本地化的激子在二聚体中的发色团之一。将这些结果与我们先前描述的双色各向异性实验的结果进行比较[J. Phys. Chem. 1995，99，15699-15704]，双色各向异性实验表明激子态间弛豫和激子态退相的时间常数分别为10-30 fs和280 fs。目前的结果表明，激子本地化和激子状态退相发生在类似的时间尺度。我们认为，激发态间弛豫和激子定位在别藻蓝蛋白三聚体提供了一个有效的机制，从发色团二聚体的能量转移相干性产生的定向能量转移。
We have employed dynamic absorption, transient hole-burning and discrete two-color pump-probe femtosecond spectroscopic methods to obtain a time-resolved view of exciton dynamics in trimers of allophycocyanin, the major component of the core of the phycobilisome in cyanobacteria. Allophycocyanin trimers contain a C-3-symmetric array of phycocyanobilin (open-chain tetrapyrrole) dimers. The femtosecond time-resolved pump-probe spectra and single-wavelength transients observed in allophycocyanin preparations were interpreted with the aid of a series of calculated spectra, which are based on an assignment of the ground-state absorption spectrum in terms of exciton-coupled chromophore dimers. The observed and calculated time-resolved pump-probe spectra indicate that interexciton-state relaxation, a radiationless transfer of population between dimer exciton states, is responsible for a red shift of the spectra on the similar to 30-fs time scale. The time evolution of the pump-probe spectra is inconsistent with a model accounting for the groundstate absorption spectrum in terms of pairs of uncoupled chromophores linked by subpicosecond Forster energy-transfer paths. On a slower time scale, extending from the 300-fs to ps delay range, the time-resolved spectra evolve in a manner consistent with localization of an exciton on one of the chromophores in a dimer. These results are to be compared with those of two-color anisotropy experiments that we previously described [J. Phys. Chem. 1995, 99, 15699-15704], which suggest time constants for interexciton-state relaxation and exciton-state dephasing of 10-30 fs and 280 fs, respectively. The present results suggest that exciton localization and exciton-state dephasing occur on similar time scales. We suggest that interexciton-state relaxation and exciton localization in allophycocyanin trimers provide a potent mechanism for directed energy transfer that arises from the energy-transfer coherence properties of chromophore dimers.