Panoramic portrait of primary molecular events preceding excited state proton transfer in water.
Panoramic portrait of primary molecular events preceding excited state proton transfer in water.
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DOI：
10.1039/c6sc00672h
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发表时间：
2016-08-01
期刊：
影响因子：
8.4
通讯作者：
Fang C
中科院分区：
文献类型：
--
作者：
Liu W;Wang Y;Tang L;Oscar BG;Zhu L;Fang C
电力超快激发态质子在水中转移的主要事件被揭示涉及耦合分子间和分子内运动。光化学为从发光和人类视觉到光捕获的许多过程提供动力。然而，在分子时间尺度上的多维光化学反应坐标的阐明仍然具有挑战性。我们发展了波长可调谐飞秒受激拉曼光谱技术，以同时实现对溶液中广泛应用的光酸吡喃进行激发态质子转移（ESPT）反应的瞬态反应物和产物物种的预共振增强。在低频区，280 cm-1环变形模式400 nm光激发后表现出显着的强度振荡的亚皮秒时间尺度上，由于非谐振动耦合到180 cm-1的氢键伸缩模式，只有在ESPT的溶剂，表明功能相关的主要事件。这导致在扩散控制分离之前在3 ps时间尺度上形成接触离子对。分子间的180 cm-1模式也揭示了振动冷却时间常数，在H2O和D2 O，这不同于ESPT的时间常数，在H2O/D2 O，分别为300/8和90/250 ps。使用H218 O的光谱结果进一步证实了分子间180 cm-1模式在调节质子供体和受体之间的距离和形成瞬态离子对中的功能作用。在光化学反应过程中，在宽光谱范围内直接观察分子结构演化，丰富了我们对势能面的基本理解，并掌握了以特殊的原子和时间精度推进能源和生物科学的关键。
Primary events that power ultrafast excited state proton transfer in water are revealed to involve coupled intermolecular and intramolecular motions. Photochemistry powers numerous processes from luminescence and human vision, to light harvesting. However, the elucidation of multidimensional photochemical reaction coordinates on molecular timescales remains challenging. We developed wavelength-tunable femtosecond stimulated Raman spectroscopy to simultaneously achieve pre-resonance enhancement for transient reactant and product species of the widely used photoacid pyranine undergoing excited-state proton transfer (ESPT) reaction in solution. In the low-frequency region, the 280 cm–1 ring deformation mode following 400 nm photoexcitation exhibits pronounced intensity oscillations on the sub-picosecond timescale due to anharmonic vibrational coupling to the 180 cm–1 hydrogen-bond stretching mode only in ESPT-capable solvents, indicating a primary event of functional relevance. This leads to the contact ion pair formation on the 3 ps timescale before diffusion-controlled separation. The intermolecular 180 cm–1 mode also reveals vibrational cooling time constants, ∼500 fs and 45 ps in both H2O and D2O, which differ from ESPT time constants of ∼3/8 and 90/250 ps in H2O/D2O, respectively. Spectral results using H218O further substantiate the functional role of the intermolecular 180 cm–1 mode in modulating the distance between proton donor and acceptor and forming the transient ion pair. The direct observation of molecular structural evolution across a wide spectral region during photochemical reactions enriches our fundamental understanding of potential energy surface and holds the key to advancing energy and biological sciences with exceptional atomic and temporal precision.
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影响因子：
2.9
作者：
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通讯作者：
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