Seeing into the Abyss: Critical Points and Paths on the S1 Potential Energy Surface of Stilbenes and beta-Carotene

洞察深渊：二苯乙烯和 β-胡萝卜素 S1 势能面的临界点和路径

• 批准号: 168757171
• 负责人: Professor Dr. Nikolaus P. Ernsting
• 金额: --
• 依托单位: Arbeitsgruppe Ultrakurzzeitspektroskopie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2010
• 资助国家: 德国
• 起止时间: 2009-12-31 至 2017-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/168757171?language=en
• 关键词: Seeing; into; Abyss; Critical; Points

Stilbene, the paradigm for photoisomerisation around a double bond, is not understood despite decades of research. (i) A phantom state at 90 deg C=C twist angle is thought to be nonexistent because of fast internal conversion. However we could stabilize it recently. (ii) The so-called stilbene enigma is unsolved: why does barrier crossing speed up in low friction solvents compared to the gas phase? (iii) Transient Raman spectra of excited cis stilbene show zero activity for reactive modes. Quantum computational chemists have serious difficulties in explaining these observations; for example no stable cis S1 point was ever calculated. The challenge is to understand the mechanisms involved. Only then one may ask whether this is general, what may be expected with bacteriorhodopsin etc. In other words, the uncertainties about stilbene must be resolved at todays´s level of theory and experiment if the same studies of photoisomerisation in biomolecules are to be credible. For this purpose Femtosecond Stimulated Raman Scattering (FSRS) was developed to a leading position worldwide. Many new S1 Raman bands were observed and assigned. In addition we showed that delicate chemical substitution opens up new ways to populate the reactive surface. This is now combined into two research lines: (1) A spectroscopic characterisation of the phantom state on the S1 PES of stilbenes, and of fast reaction paths leading to it, will provide benchmarks for computations of electronic structure and reactivity. (2) Vibrational energy flow will be monitored via linewidths and anti-Stokes intensities. The approach will first be applied to excited beta-carotene (because it is a most intense Raman scatterer) and then to excited stilbenes.Together we shall specify accurately the surface regions and processes which are associated with problems (I,ii,iii), and thus contribute to their solution.

二苯乙烯是围绕双键进行光异构化的范例，尽管进行了数十年的研究，但仍不为人所知。(I)90°C=C扭角的虚态由于快速的内转换而被认为是不存在的。然而，我们最近可以稳定它。(Ii)所谓的二苯乙烯之谜尚未解开：为什么在低摩擦溶剂中的势垒穿越速度比在气相中更快？(3)激发态顺式二苯乙烯的瞬时拉曼光谱对反应模式的活性为零。量子计算化学家很难解释这些观测结果；例如，没有计算出稳定的顺式S1点。挑战在于理解其中涉及的机制。只有到那时，人们才会问这是否是一般性的，细菌视紫红质等可能会带来什么。换句话说，如果生物分子中光异构化的相同研究要可信，关于二苯乙烯的不确定性必须在当今S的理论和实验水平上得到解决。为此，飞秒受激拉曼散射(FSRs)在世界范围内处于领先地位。观察到并归属了许多新的S1拉曼谱带。此外，我们还展示了精细的化学取代开辟了填充活性表面的新途径。这现在结合成两个研究方向：(1)二苯乙烯类化合物S1PES上幻影态的光谱表征，以及通向它的快速反应路径的光谱表征，将为电子结构和反应性的计算提供基准。(2)振动能流将通过线宽和反斯托克斯强度进行监测。这种方法将首先应用于激发的β-胡萝卜素(因为它是最强的拉曼散射体)，然后应用于激发的二苯乙烯类化合物。我们将一起精确地指定与问题(I、II、III)相关的表面区域和过程，从而有助于它们的解决。