Multiphoton Processes and Directional Charge-Transfer in Ferrocene-Polyoxometalate Dyads and Triads

分子金属氧化物，即所谓的聚氧乙烯酸盐（POM）是用于设计多功能光引发反应体系的通用平台分子。POM可以充当用于设计捕光二联体的平台分子，因为它们适合于与光吸收金属络合物（此处为二茂铁（Fc））以及质子/电子供体共价官能化。二茂铁-POM二元体是理想的模型系统，因为申请人最近已经证明了两种组分之间的电子耦合和电荷转移。此外，二茂铁和POM的电子结构和氧化还原性质可以在分子水平上进行调整。此外，POM可以使电子在多个金属中心之间离域，从而为设计具有长寿命电荷分离态的二元体提供了充足的机会。此外，二茂铁的化学改性使得能够调节（光）氧化还原性质，从而控制光吸收和电荷转移到POM。因此，这些系统对于光捕获和能量转换社区具有巨大的兴趣，并且已经证明了POM二分体上的光驱动的多电子电荷积累以及随后的电荷转移，例如转移到光电极。在本论文中，我们将研究Fc-POM二联体和三联体的基本物理性质和光诱导超分子性质。我们的具体重点是合理化可见光诱导的电荷分离态的形成和性质，并使用时间分辨光谱和光谱电化学的见解来指导组件调谐工作。这将导致系统能够从外围基团到POM的定向（多个）电子转移。一个具体的优势和挑战将是电子和抗衡阳离子（例如质子）转移的耦合。我们提出，这一概念可以降低高能电子转移势垒，导致有效的电荷分离，长的电荷分离态寿命，并使研究的多光子，多电子转移的Fc-POM二联体和三联体。

Molecular metal oxides, so-called polyoxometalates (POMs) are versatile platform molecules for the design of multifunctional light-triggered reaction systems. POMs can act as platform molecules for the design of light-harvesting dyads as they are amenable for covalent functionalization with light-absorbing metal complexes, here ferrocene (Fc), as well as proton/electron donors. Ferrocene-POM dyads are ideal model systems as electronic coupling and charge-transfer between both components has recently been demonstrated by the applicants. In addition, the electronic structures and redox properties of ferrocene and POM can be adapted on the molecular level. Also, POMs can delocalize electrons across multiple metal centers, thereby offering ample opportunities for the design of dyads with long-lived charge-separated states. In addition, chemical modification of the ferrocene enables tuning of the (photo-)redox-properties and thus control light-absorption and charge transfer to the POM. Thus, these systems are of immense interest for the light-harvesting and energy conversion communities, and light-driven multi-electron charge-accumulation on POM dyads, as well as subsequent charge transfer, e.g. to photoelectrodes, has been demonstrated. Their roles in applications such as photovoltaics, photo-electrochemistry and light-driven water splitting are actively explored.In this proposal, we will study the fundamental photophysical and light-induced supramolecular properties of Fc-POM dyads and triads. Our specific focus is to rationalize the visible-light-induced formation and properties of charge-separated states and use time-resolved spectroscopic and spectro-electrochemical insights to direct component tuning efforts. This will lead to systems capable of directional (multiple) electron transfer from the peripheral groups to the POM. A specific advantage and challenge will be the coupling of electron and counter-cation (e.g. proton) transfer. We propose that this concept can reduce energetic electron-transfer barriers, resulting in efficient charge-separation, long charge-separated state lifetimes, and enable the study of multi-photon, multi-electron transfers in Fc-POM dyads and triads.