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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >A simple artificial light-harvesting dyad as a model for excess energy dissipation in oxygenic photosynthesis
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A simple artificial light-harvesting dyad as a model for excess energy dissipation in oxygenic photosynthesis

机译：一个简单的人工光收集二元体作为氧气光合作用中多余能量消散的模型

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Under excess illumination, plant photosystem 11 dissipates excess energy through the quenching of chlorophyll fluorescence, a process known as nonphotochemical quenching. Activation of nonphotochemical quenching has been linked to the conversion of a carotenoid with a conjugation length of nine double bonds (violaxanthin) into an 11-double-bond carotenoid (zeaxanthin). It has been suggested that the increase in the conjugation length turns the carotenoid from a nonquencher into a quencher of chlorophyll singlet excited states, but unequivocal evidence is lacking. Here, we present a transient absorption spectroscopic study on a model system made up of a zinc phthalocyanine (PC) molecule covalently linked to carotenoids with 9, 10, or 11 conjugated carbon-carbon double bonds. We show that a carotenoid can act as an acceptor of PC excitation energy, thereby shortening its singlet excited-state lifetime. The conjugation length of the carotenoid is critical to the quenching process. Remarkably, the addition of only one double bond can turn the carotenoid from a nonquencher into a very strong quencher. By studying the solvent polarity dependence of the quenching using target analysis of the time-resolved data, we show that the quenching proceeds through energy transfer from the excited PC to the optically forbidden S, state of the carotenoid, coupled to an intramolecular charge-transfer state. The mechanism for excess energy dissipation in photosystem 11 is discussed in view of the insights obtained on this simple model system.
机译：在过度照射下，植物光系统11通过叶绿素荧光的猝灭（称为非光化学猝灭）的过程消散了多余的能量。非光化学猝灭的激活与共轭长度为9个双键的类胡萝卜素（紫黄质）转化为11个双键类胡萝卜素（玉米黄质）有关。已经提出，缀合长度的增加将类胡萝卜素从非猝灭剂转变为叶绿素单重态激发态的猝灭剂，但是缺乏明确的证据。在这里，我们对由锌酞菁（PC）分子共价连接至具有9、10或11个共轭碳-碳双键的类胡萝卜素的模型系统进行了瞬态吸收光谱研究。我们表明，类胡萝卜素可以充当PC激发能的受体，从而缩短其单线态的激发态寿命。类胡萝卜素的共轭长度对于淬灭过程至关重要。值得注意的是，仅添加一个双键可将类胡萝卜素从非猝灭剂转变为非常强的猝灭剂。通过使用时间分辨数据的目标分析研究淬灭的溶剂极性依赖性，我们表明淬灭是通过能量从激发的PC转移到光学禁止的S（类胡萝卜素的状态）以及分子内电荷转移进行的州。鉴于在此简单模型系统上获得的见解，讨论了光系统11中多余能量耗散的机制。

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