Excitonic coupling and delocalized states in the excited state dynamics of nucleotide oligomers.

许多不同材料的功能是由它们各自的构建块之间的相互作用决定的。相邻发色团之间的激子耦合是理解和发展分子光子和电子器件的关键。它控制单个单体之间的能量和电荷转移。在该项目的框架内，将开发一种新的实验方法，将液体样品的时间分辨光电子能谱与圆二色性相结合，从而为手性分子的激子耦合提供直接的实验途径。这种方法将被应用到单链DNA/RNA构建块在水溶液中的离域状态（特别是激子状态）的光稳定性的这些分子的作用进行调查。虽然单个DNA碱基的分子物理学已经相当好地理解了，但DNA（单链或双链）的分子物理学仍然提出了许多问题。DNA和RNA具有非凡的光稳定性，因此是地球上生命发展的基础，特别是在臭氧层尚未形成的情况下，其背后的机制是什么？为什么光诱导的损伤在DNA/RNA中的特定位点比在其他位点更常见？为什么RNA比DNA更耐光？这些都是在本项目框架内调查的中心问题。特别强调的是离域状态的核心作用，这些分子的物理学。我们将研究不同链长的DNA/RNA寡聚体。DNA/RNA碱基之间的电子耦合以及光学布居的Frenkel激子的寿命都可以直接从实验数据中提取。Frenkel激子在电荷转移复合物的形成下衰减，即。e.电荷分离时间分辨光电子能谱将研究这些电荷转移态的电子结构、它们的空间范围和它们的时间演化。碱基序列依赖的结果允许的结论的关键参数的光弛豫。离域状态的作用以及某些结构参数的影响将被详细研究。

Function of many different materials is determined by the interaction between their individual building blocks. Excitonic coupling between adjacent chromophores is key to understanding and development of molecular photonic and electronic devices. It controls energy and charge transfer between individual monomers. In the frame of this project, a new experimental method will be developed that combines time-resolved photoelectron spectroscopy of liquid samples with circular dichroism and thereby provides direct experimental access to the excitonic coupling of chiral molecules. This method will be applied to single-stranded DNA/RNA building blocks in aqueous solution to investigate the role of delocalized states (in particular of excitonic states) for the photostability of those molecules. While the photophysics of individual DNA bases is reasonably well understood, the photophysics of DNA (single- or double-stranded) still raises many questions. What is the mechanism behind the extraordinary photostability of DNA and RNA and is therefore basis for the development of life on earth - in particular, when the ozon layer has not yet developed? Why do photoinduced lesions develop more often at specific sites in DNA/RNA than at others? Why is RNA more photostable than DNA? These are the central questions which are investigated in the frame of this project. Special emphasis is on the central role of delocalized states for the photophysics of those molecules. We will investigate DNA/RNA oligomers of different chain lengths. Both, the electronic coupling between the DNA/RNA bases as well as the lifetime of the optically populated Frenkel excitons are directly extractable from the experimental data. Frenkel excitons decay under formation of charge-transfer complexes, i. e. charge separation. Time-resolved photoelectron spectroscopy will investigate the electronic structure of those charge-transfer states, their spatial extent and their temporal evolution. Base-sequence dependent results allow conclusions on the key parameters in the photorelaxation. The role of delocalized states as well as the influence of certain structural parameters will be investigated, in detail.