Excited-state proton transfer (ESPT): Investigations on the single-molecule level for separating solvation from intrinsic reaction dynamics

激发态质子转移（ESPT）：在单分子水平上研究从固有反应动力学中分离溶剂化作用

• 批准号: 288875784
• 负责人: Professor Dr. Gregor Jung
• 金额: --
• 依托单位: Professur für Biophysikalische Chemie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2016
• 资助国家: 德国
• 起止时间: 2015-12-31 至 2018-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/288875784?language=en
• 关键词: Excited; state; proton; transfer; ESPT

Proton-transfer reactions are amongst the most important chemical transformations. One theoretical and successful approach for its description is based on Marcus-theory which is known for its relevance in electron-transfer reactions. In contrast to this latter reaction type, proton-transfer reactions in the excited-state (ESPT) are known which are associated with bright fluorescence emission. In this special case, the photoacid and the conjugated base exhibit dual emission, i.e. both are fluorescent with different colors. After emission, the proton is shuffled back to the conjugated base and the system is consequently reset in its initial state. These properties enable the observation of an individual reaction multiple times by means of single-molecule fluorescence spectroscopy. We recently synthesized and described a variety of photostable photoacids which undergo ESPT even in a solid matrix. By recording the fluorescence intensities of both the photoacid and the conjugated base as well as the kinetics of ESPT in a temperature-dependent manner, we seek to determine the activation energy as well the free energy of a single elementary reaction. As we expect to meet varying geometries for the photoacid/proton-acceptor pair, these experiments will enable to address the distance dependence of proton-transfer reactions. Preliminary antibunching experiments show that the backreaction in the electronic ground state does not reflect the kinetics of proton diffusion, but allows for studying the kinetics of individual photocycles. Alternatively, varying compositions in the system photoacid/proton-acceptor/surrounding can be resolved from which the solvation contribution to the reaction dynamics can be separated from intrinsic contributions. Our long-term goal is to combine these approaches and to roughly sketch a potential-energy surface of a simple reaction only by experimental means.

质子转移反应是最重要的化学转化之一。描述它的一种理论上和成功的方法是基于马库斯理论，该理论以其在电子转移反应中的相关性而闻名。与后一种反应类型相反，激发态的质子转移反应(ESPT)与明亮的荧光发射有关。在这种特殊情况下，光酸和共轭碱表现出双重发射，即两者都是不同颜色的荧光。在发射后，质子被洗牌回共轭碱基，因此系统被重置为其初始状态。这些特性使得能够通过单分子荧光光谱多次观察单个反应。我们最近合成并描述了一系列即使在固体基质中也能进行ESPT的光稳定性光酸。通过记录光酸和共轭碱的荧光强度以及ESPT的动力学随温度变化的方式，我们寻求确定单个基元反应的活化能和自由能。由于我们预计会遇到光酸/质子-受体对的不同几何结构，这些实验将能够解决质子转移反应的距离依赖关系。初步的反聚束实验表明，电子基态的反向反应并不反映质子扩散的动力学，但可以用来研究单个光循环的动力学。或者，可以分解体系中光酸/质子受体/环境中的不同组成，从中可以将溶剂化对反应动力学的贡献与本征贡献分开。我们的长期目标是将这些方法结合起来，仅通过实验手段粗略地绘制出简单反应的势能面。