Multidimensional Spectroscopy of Exciton Dynamics

电子激发的相干二维(2D)和高维光谱提供了关于复杂系统随时间变化的动力学的详细信息。利用对多个频率轴的非线性信号的分析，可以分离在一维频谱中重叠的贡献。我们的目标是：进一步发展二维光谱技术，以实现魔角下的快速逐炮数据采集(即避免各向异性贡献)。由此，我们将研究分子聚集体中的激子动力学。通过与伍特纳教授的合作)，氢键导致了发色团的独特排列，形成了一种“索状”的双链结构，这种结构可以通过改变取代基来系统地改变。我们希望通过2D光谱和功率相关的测量来确定激子信号作为结构的函数。快速的2D数据采集将使我们能够进一步跟踪激子耦合在自聚集动力学过程中随时间的演化。在另一个项目部分(与兰伯特教授的合作)，我们想要调查在2D光谱学文献中有争议地讨论的长寿命相干的起源。方烷低聚物适合作为模型体系，因为一个生色团的最强吸收与另一个生色团的振动肩有光谱重叠。除了线性低聚物外，我们还将讨论环形和星形结构，因为光学跃迁的选择规则会随着不同的对称性而改变，进而改变激子能量转移的通道。在该项目的另一部分中，我们将开发一种在文献中是新的技术，我们称之为“2D显微光谱学”，允许在共焦显微镜中增加空间分辨率。因此，我们将研究在表现出局部变化的激子性质的表面上的微晶分子聚集体(与Pflum教授合作)。最后一部分以理论分析为中心。除了与理论小组(恩格尔教授、恩格斯教授、米特里克教授)合作外，我们还想开发一种从2D光谱中提取布居迁移率的新方法。在文献中，人们精心地对分子系统进行建模，模拟动力学，由此计算出非线性响应和可观测信号，并将结果与实验进行比较，最后迭代地改进模型假设。取而代之的是，我们努力实现对实验原始数据的直接“反转”。我们希望将瞬变吸收的“目标分析”原理应用于2D光谱学，并将其与系统的“Aufbau原理”相结合。

Coherent two-dimensional (2D) and higher-dimensional spectroscopy of electronic excitations provides detailed information on the time-dependent dynamics of complex systems. Making use of the analysis of nonlinear signals with respect to multiple frequency axes it is possible to separate contributions that overlap in one-dimensional spectra. We have the following objectives: The technique of 2D spectroscopy shall be further developed to implement fast shot-to-shot data acquisition under the magic angle (i.e., avoiding anisotropy contributions). With that we will investigate the excitonic dynamics in molecular aggregates. In a perylene-based J-aggregate (cooperation with Prof. Würthner), H-bonds lead to a unique arrangement of the chromophores in a "cable-like" double-strand structure that can be varied systematically by changing the substituents. We want to determine the excitonic signatures as a function of structure via 2D spectroscopy as well as power-dependent measurements. The fast 2D data acquisition should further allow us to follow the time-dependent evolution of excitonic couplings during the kinetic process of selfaggregation. In another project part (cooperation with Prof. Lambert) we want to investigate the origin of long-lived coherences that are discussed controversially in the literature on 2D spectroscopy. Squarain oligomers are suited as model systems because there the most intense absorption of the one chromophore overlaps spectrally with the vibrational shoulder of the other chromophore. Besides linear oligomers we will also address ring- and star-shaped structures because the selection rules for optical transitions change with the different symmetries, in turn modifying the channels accessible for excitonic energy transfer. In yet another part of the project we will develop a technique that is new in the literature and that we call "2D micro-spectroscopy" allowing additional spatial resolution in a confocal microscope. Thus we shall investigate microcrystalline molecular aggregates on surfaces that exhibit locally varying excitonic properties (cooperation with Prof. Pflaum). The last project part centers on theoretical analysis. Besides cooperations with the theory groups (Prof. Engel, Prof. Engels, Prof. Mitric) we want to develop a new procedure for extracting population transfer rates from 2D spectra. In the literature one models elaborately, for this purpose, the molecular system, simulates the dynamics, from that calculates the nonlinear response and the observable signal, compares the result with experiment, and finally improves the model assumptions iteratively. Instead, we strive for a direct "inversion" of the experimental raw data. We want to adapt for 2D spectroscopy the principle of "target analysis" known from transient absorption and combine it with a systematic "Aufbau principle".