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

分子金属氧化物，即多金属氧酸盐（pom）是设计多功能光触发反应体系的多功能平台分子。pom可以作为设计光收集二偶体的平台分子，因为它们可以与吸收光的金属配合物（这里是二茂铁（Fc））以及质子/电子给体进行共价功能化。二茂铁-聚甲醛二元体是理想的模型系统，因为电子耦合和电荷转移在两个组件之间最近被申请人证明。此外，二茂铁和聚甲醛的电子结构和氧化还原性能可以在分子水平上进行调整。此外，pom可以跨多个金属中心使电子离域，从而为设计具有长寿命电荷分离状态的二极体提供了充足的机会。此外，对二茂铁进行化学修饰可以调节（光）氧化还原性能，从而控制光吸收和电荷向POM的转移。因此，这些系统对于光收集和能量转换社区具有巨大的兴趣，并且已经证明了POM二极体上的光驱动多电子电荷积累以及随后的电荷转移，例如光电极。它们在光伏、光电化学和光驱动水分解等应用中的作用正在积极探索。在本论文中，我们将研究Fc-POM二元和三元的基本光物理和光诱导超分子性质。我们的重点是使可见光诱导的电荷分离态的形成和性质合理化，并利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。这将导致系统能够定向（多个）电子从外围基团转移到POM。一个特殊的优势和挑战将是电子和反阳离子（如质子）转移的耦合。我们提出这个概念可以减少高能电子转移障碍，从而产生有效的电荷分离，长电荷分离态寿命，并使Fc-POM二联体和三联体中的多光子，多电子转移研究成为可能。

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.