Control of the entatic state by targeted optical excitation of the ligand sphere

内在态的概念描述了电荷转移和伴随的结构重排之间的矛盾关系。它提出了一个根本性的问题，即电荷转移是否受到结构性前组织的青睐。这个问题对于许多具有催化活性的化学体系来说是至关重要的，在这些体系中，过渡金属络合物的催化性能是由它们定制的配体球体控制的。在生物无机化学方面，几个小组已经报道了植物模型系统。这些模型体系具有结构上预先组织的配位体球体。一个事实阻碍了系统的研究，因为具有可调前组织的系统不容易通过化学合成。我们已经证明，光激发的电荷转移导致一种状态，这对应于电荷从过渡金属到配体系统的完全转移。因此，本项目集中于对稳定的模型系统的配体系统的定向光学操纵，以激发配体的预组织。因此，我们通过与配体振动相适应的中红外泵浦光束来激发，这会将一种内态调谐到另一种态。这一过程是在振动激励的发射下进行的。泵浦光束的功率现在可以精确地控制振动激发。不同红外主动模式的激发使得能够有针对性地选择预先组织的系统的不同激发模式。相比之下，在可见光或紫外光范围内的常规激发通过激发进入高度激发的电子态，触发了一个高度复杂的过程，最终进入光激活的电子态。在这个项目中，这些状态的研究将通过UV/VIS或IR泵浦拉曼探测实验来实现，并辅之以瞬时吸收测量和时间分辨荧光。我们将在这项研究中回答如何区分电子激发到电荷转移跃迁和中红外光谱范围内配体体系的结构激发。具体地说，我们的目标是阐明量身定制的激发是否会转化为配体系统的本征模，并促进本征态之间的跃迁。这将最终导致一个问题的答案，即光在多大程度上可以控制和操纵本征态。

The concept of the entatic state describes the ambivalent relation of a charge transfer and an accompanying structural rearrangement. It poses the fundamental question if the charge transfer is favoured by a structural pre-organisation. This question is essential for many catalytically active systems in chemistry where the catalytic properties of transition metal complexes are controlled by their tailored ligand sphere. In bioinorganic chemistry, several groups have reported entatic model systems. These model systems possess structurally preorganised ligand spheres. A systematic study is impeded by the fact that systems with a tunable preorganisation are not easily chemically synthesised. We have shown earlier that the optically excited charge transfer leads to a state, which corresponds to a complete transfer of charge from the transition metal to the ligand system.This project focuses, thus, on the targeted optical manipulation of the ligand systems of a stable model system for an entatic state in order to excite the preorganisation of the ligands. Therefore, we excite via a mid-infrared pump beam suited ligand vibrations, which tune an entatic state into another one. This process proceeds under emission of vibrational excitations. The power of the pump beam allows now the exact control of the vibrational excitation. The excitation of different infrared-active modes enables the targeted selection of different excitation patterns of preorganised systems. In contrast, the conventional excitation in the visible or ultraviolet spectral range triggers a highly complex process cascade by the excitation into highly ecited electronic states, which finally ends up in a photoactivated entatic state. The investigation of these states shall be realised in this project complementary by UV/VIS- or IR-pump Raman-probe experiments, which are complemented by transient absorption measurements and time-resolved fluorescence. We will answer in this study how the dynamics of the entatic state differentiates between the electronic excitation into the charge transfer transition and the structural excitation of the ligand systems in the mid IR range. In detail, we target to clarify if the tailored excitation into eigenmodes of the ligand system and facilitate the transition between entatic states. This would finally lead to an answer of the question how far entatic states can be controlled and manipulated by light.