Schödel R, Hillmann F, Schrötter T, Voigt J, Irrgang K D, Renger G
AG Molekulare Biophysik und Spektroskopie, Humboldt Universität zu Berlin, Germany.
Biophys J. 1996 Dec;71(6):3370-80. doi: 10.1016/S0006-3495(96)79530-9.
Relative fluorescence yield, phi F, and transmittance, T, were measured in solubilized light-harvesting complex II (LHCII) as a function of photon density, Ip, of monochromatic 645-nm laser pulses (duration: approximately 2.5 ns). Special efforts were made in constructing an optical set-up that allows the accurate determination of the fluorescence from an area of constant Ip, phi F(Ip) starts to decline at approximately 10(14) and drops to values below 0.01% at maximum Ip (approximately 10(19) photons cm-2 pulse-1). T(Ip) decreases only slightly at photon densities of approximately 10(15) but increases steeply at values of > 10(17) photons cm-2 pulse-1. The interpretation of the phi F(Ip) data using the saturation limit of Mauzerall's multiple hit model leads to a unit size of about 10-15 chlorophyll molecules. One interpretation is to attribute this result to a very fast exciton-exciton annihilation of multiple excited states generated within this small domain. Alternatively, based on the assumption that delocalized cluster states within the monomeric/trimeric subunit of LHCII exist, the results can be consistently described by a kinetic model comprising ground, monoexcitonic, and biexcitonic states of clusters and a triplet state that is quenched by carotenoids in LHCII. Within the framework of this model the annihilation of multiple excitations is explained as ultrafast radiationless relaxation of higher excited cluster states. Comparative measurements in diluted acetonic Chl a solution are consistently described by the depletion of the ground state, taking the absorption cross section at the used wavelength.
在溶解的光捕获复合物II（LHCII）中，测量了相对荧光产率（φF）和透光率（T），作为单色645 nm激光脉冲（持续时间：约2.5 ns）光子密度（Ip）的函数。在构建光学装置时付出了特别努力，该装置能够准确测定来自恒定Ip区域的荧光，φF（Ip）在约10¹⁴时开始下降，并在最大Ip（约10¹⁹光子·cm⁻²·脉冲⁻¹）时降至低于0.01%的值。T（Ip）在约10¹⁵的光子密度下仅略有下降，但在>10¹⁷光子·cm⁻²·脉冲⁻¹时急剧增加。使用Mauzerall多击模型的饱和极限对φF（Ip）数据进行解释，得出单位大小约为10⁻¹⁵个叶绿素分子。一种解释是将该结果归因于在这个小区域内产生的多个激发态的非常快速的激子 - 激子湮灭。或者，基于LHCII单体/三聚体亚基内存在离域簇态的假设，结果可以由一个动力学模型一致地描述，该模型包括簇的基态、单激子态和双激子态以及一个被LHCII中的类胡萝卜素淬灭的三重态。在该模型的框架内，多个激发的湮灭被解释为更高激发簇态的超快无辐射弛豫。在稀释的丙酮叶绿素a溶液中的比较测量通过基态的耗尽得到一致描述，同时考虑了所用波长处的吸收截面。
