Conical intersection dynamics of the primary photoisomerization event in vision
Conical intersection dynamics of the primary photoisomerization event in vision
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DOI：
10.1038/nature09346
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发表时间：
2010-09-23
期刊：
影响因子：
64.8
通讯作者：
Cerullo, Giulio
中科院分区：
文献类型：
--
作者：
Polli, Dario;Altoe, Piero;Cerullo, Giulio
自从视紫红质中11顺式视网膜生色团转变为全反式发色团被确认为视觉中的主要光化学事件以来，实验学家和理论家一直试图揭开这一过程的分子细节。量子产额为0.65(参考文献)。2)，在短短200飞秒内产生初级基态视紫红质光产物(参考文献3-7)，以及在第一个稳定的底视紫红质中间体(8)中储存相当大的能量，这些都表明了一种异常快速和有效的光激活单向反应(9)。视紫红质的独特反应性通常归因于基态和激发电子态(10，11)的势能面之间的锥形相交，使得光子能量能够高效和超快地转化为化学能(12-16)。但是，获得有关锥形交叉的直接实验证据是具有挑战性的：反应分子的电子态之间的能隙在超短时间尺度上发生显著变化，这需要结合高时间分辨率和宽光谱观察窗口的观测方法。在这里，我们展示了时间分辨率低于20微秒，光谱覆盖范围从可见光到近红外的超快光学光谱，这使得我们能够跟踪导致视紫红质异构化的锥形交叉点的动力学。我们通过监测反应物发射的损失和随后出现的光产物吸收来跟踪从光激Franck-Condon区到光产物的相干波包运动，并发现实验观察和涉及真正电子态交叉的分子动力学计算之间有很好的一致性。综上所述，这些发现构成了迄今为止最令人信服的证据，证明了锥形交叉点的存在及其在视觉光化学中的重要性。
Ever since the conversion of the 11-cis retinal chromophore to its all-trans form in rhodopsin was identified as the primary photochemical event in vision(1), experimentalists and theoreticians have tried to unravel the molecular details of this process. The high quantum yield of 0.65 (ref. 2), the production of the primary ground-state rhodopsin photoproduct within a mere 200 fs (refs 3-7), and the storage of considerable energy in the first stable bathorhodopsin intermediate(8) all suggest an unusually fast and efficient photoactivated one-way reaction(9). Rhodopsin's unique reactivity is generally attributed to a conical intersection between the potential energy surfaces of the ground and excited electronic states(10,11) enabling the efficient and ultrafast conversion of photon energy into chemical energy(12-16). But obtaining direct experimental evidence for the involvement of a conical intersection is challenging: the energy gap between the electronic states of the reacting molecule changes significantly over an ultrashort time-scale, which calls for observational methods that combine high temporal resolution with a broad spectral observation window. Here we show that ultrafast optical spectroscopy with sub-20-fs time resolution and spectral coverage from the visible to the near-infrared allows us to follow the dynamics leading to the conical intersection in rhodopsin isomerization. We track coherent wave-packet motion from the photoexcited Franck-Condon region to the photoproduct by monitoring the loss of reactant emission and the subsequent appearance of photoproduct absorption, and find excellent agreement between the experimental observations and molecular dynamics calculations that involve a true electronic state crossing. Taken together, these findings constitute the most compelling evidence to date for the existence and importance of conical intersections in visual photochemistry.