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

内态的概念描述了电荷转移和伴随的结构重排的矛盾关系。它提出了一个基本问题，即电荷转移是否受到结构性预组织的青睐。这个问题对于化学中许多催化活性体系来说是必不可少的，在这些体系中，过渡金属配合物的催化性能是由它们定制的配体球体控制的。在生物无机化学中，几个小组已经报道了内部模型系统。这些模型系统具有结构上预先组织的配体球。具有可调预组织的系统不容易化学合成，这一事实阻碍了系统研究。我们前面已经表明，光激发的电荷转移导致一个状态，这对应于从过渡金属到配体系统的电荷完全转移。因此，这个项目的重点是对一个稳态模型系统的配体系统进行有针对性的光学操作，以激发配体的预组织。因此，我们通过适合配体振动的中红外泵浦光束激发，将一个内在状态调整为另一个状态。这一过程在振动激励下进行。泵浦光束的功率现在可以精确地控制振动激励。不同红外主动模式的激发使预先组织系统的不同激发模式的目标选择成为可能。相比之下，在可见光或紫外光谱范围内的传统激发触发了一个高度复杂的过程级联，通过激发到高激发的电子态，最终结束于光激活的内吸态。对这些状态的研究将在本项目中实现，辅以UV/VIS或ir泵浦拉曼探针实验，并辅以瞬态吸收测量和时间分辨荧光。在这项研究中，我们将回答在中红外范围内，内定态的动力学如何区分电子激发到电荷转移跃迁和配体系统的结构激发。详细地说，我们的目标是澄清是否定制激发到配体系统的本征模式，并促进内部状态之间的过渡。这将最终导致一个问题的答案，即在多大程度上原子状态可以被光控制和操纵。

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.