Structural control of the electronic coupling between donor and photosensitizer in molecular dyads via modification of a peripheral ligand

光致电子传递是自然光合作用和人工光合作用的基本过程。与自然光合作用相比，在自然光合作用中，电子转移发生在高产量并导致形成长寿命电荷分离态，而合成具有特定控制电子转移性质的(超)分子结构是一个具有挑战性的且通常是迭代的过程。根据半经典马库斯理论，为了有针对性地合成和优化具有分子内光诱导电子转移性质的分子供体-受体体系，需要详细了解潜在的结构-动力学关系，特别是分子结构与电子耦合(|H_DA|^2)、重组能(λ)和驱动力([-∆G]^*)之间的相互作用，这些参数是(分子内)电子转移的中心参数。分子结构对λ和[-∆G]^*的影响是众所周知的。相比之下，决定处于电子激发态的光敏剂和与其化学连接的施主之间的电子耦合的结构因素要直观得多，通常情况下，要孤立地描述不同结构因素对|H_DA|^2的影响是具有挑战性的。本项目的目的是定量地确定一类基于Ru(II)-多吡啶类光敏剂(作为受体)和共价连接电子给体的分子二联体从给体到光激发受体的还原电子转移的电子耦合|H_DA|^2。本项目的光谱理论工作旨在系统地推导光敏剂外围配体的结构修饰对电子转移影响的结构-机理关系，即不连接光活性中心和电子给体的配体。

Photoinduced electron transfer is a fundamental process in natural and artificial photosynthesis. Compared to natural photosynthesis, where electron transfer occurs in high yields and leads to the formation of long-lived charge separated states, the synthesis of (supra)molecular structures with specifically controlled electron transfer properties is a challenging and usually iterative process. The targeted synthesis and optimization of molecular donor-acceptor systems with tailor-made properties with respect to of an intramolecular photoinduced electron transfer requires a detailed understanding of the underlying structure-dynamics relationships and in particular the interaction between molecular structure and electronic coupling (|H_DA |^2), reorganization energy (λ) and driving force (〖-∆G〗^*), which are the central parameters for (intramolecular) electron transfer according to the semi-classical Marcus theory. The influence of molecular structure on λ and 〖-∆G〗^* is generally well understood. In contrast, the structural factors determining the electronic coupling |H_DA |^2 between a photosensitizer in the electronically excited state and a donor chemically linked to it are much less intuitive and in general it is challenging to describe the effects of different structural factors on |H_DA |^2 in photoactive transition metal complex dyads in isolation. The aim of this project is to quantitatively determine the electronic coupling |H_DA |^2 for reductive electron transfer from the donor to the photoexcited acceptor for a class of molecular dyads based on a Ru(II)-polypyridine-based photosensitizer (as acceptor) and a covalently linked electron donor. The spectroscopic-theoretical work of this project aims at the systematic deduction of structure-mechanism relationships with respect to the influence of electron transfer by structural modification of the peripheral ligands of the photosensitizers, i.e. the ligands that do not link the photoactive center with the electron donor.