Light-Driven Charge Accumulation Based on Earth-Abundant High-Potential Photosensitizers (CA-HiPoPS)

光致电子转移是自然光合作用的一个基本反应步骤，在将太阳光转化为生物物质的过程中起着关键作用。单电子的转移现在已经很好地理解了，但多电子的转移和积累仍然极具挑战性。人工光合作用主要依赖于多电子转移反应，因为低能量输入分子转化为高能量产物本质上涉及多个氧化还原事件。在此背景下，该联盟将开发光驱动多种氧化还原当量积累的新概念，以揭示其基本操作原理。我们的目标是取得三个概念上的关键进展：(1)我们将使用由丰富的过渡金属制成的新型光敏剂，与已知的贵金属基光敏剂相比，它们具有更高的还原能力；(2)我们将开发新的分子电子存储单元，帮助我们利用氧化还原电位反转的概念来促进氧化还原当量的光驱动积累；(3)我们将使用最先进的双脉冲双色泵浦-泵浦-探针紫外-可见吸收光谱来监测多个电子的连续转移。在计算化学的指导下，项目第一阶段将重点关注基于钼(0)配合物的高电位光敏剂（hipop）的设计和开发。第二个项目阶段将集中于新型光敏剂-受体（PS-A）二元体的合成、光化学表征和理论理解，其受体能够存储多达两个电子，例如众所周知的萘二亚胺受体，其中一次还原比二次还原在热力学上更容易进行。与此同时，项目二期将开发和探索具有氧化还原电位反转的新型电子受体。新的受体（TTP; 4,5,9,10-四噻apyrene和TBP， [1,1 ':4 ',1 " -terphenyl]-2,2 ',2 ",5 ' -bis(dithiin)）将能够积累和储存多达四个氧化还原等价物，它们将与两个hipop单元共价连接，形成PS-A-PS三联体。第三个项目阶段的目标是完全集成的（全共价）分子pentads D- ps - a - ps -D，由两个外围TMPD （N，N,N ',N ' -四甲基-对苯二胺）供体D通过两个Mo0 hipop连接到中央TTP受体单元a。三个参与团队在多吡啶配体和金属配合物设计，异氰化物螯合物以及4d6金属配合物中长寿命MLCT激发态的计算定制方面提供互补的专业知识。这三个团队在光诱导电子转移反应性方面有着互补的背景和专业知识，包括生物激发的耦合电子和质子转移，激发态电荷转移过程的理论方面，以及分子系统中光驱动的电荷积累。

Photoinduced electron transfer is an elementary reaction step of natural photosynthesis and as such plays a key role in the conversion of sunlight into biological matter. The transfer of single electrons is nowadays fairly well understood, but the transfer and accumulation of multiple electrons has remained extremely challenging. Artificial photosynthesis crucially relies on multi-electron transfer reactions, because the conversion of low-energy input molecules into higher-energy products intrinsically involves multiple redox events. Against this background, this consortium will develop new concepts for the light-driven accumulation of multiple redox equivalents to unravel its basic operating principles. We aim to make three conceptual key advances: (1) We will use new photosensitizers made from abundant transition metals featuring higher reducing power than well-known precious metal-based photosensitizers; (2) We will develop new molecular electron storage units that help us exploit the concept of redox potential inversion to facilitate the light-driven accumulation of redox equivalents; (3) We will use state-of-the-art two-pulse two-color pump-pump-probe UV-Vis absorption spectroscopy to monitor the consecutive transfer of multiple electrons. The first project phase will focus on high-potential photosensitizer (HiPoPS) design and development based on molybdenum(0) complexes, guided by computational chemistry. The second project phase will concentrate on synthesis, photochemical characterization and theoretical understanding of novel photosensitizer-acceptor (PS-A) dyads with acceptors capable of storing up to two electrons, e. g. the well-known naphthalene diimide acceptor, in which the primary reduction is thermodynamically easier to perform than secondary reduction. In parallel, the second project phase will develop and explore new types of electron acceptors featuring redox potential inversion. The new acceptors (TTP; 4,5,9,10-tetrathiapyrene and TBP, [1,1’:4’,1’’-terphenyl]-2,2’,2’’,5’-bis(dithiin)) will be able to accumulate and store up to four redox equivalents, and they will be covalently connected with two HiPoPS units giving PS-A-PS triads. The third project phase targets fully integrated (all-covalent) molecular pentads D-PS-A-PS-D comprised of two peripheral TMPD (N,N,N’,N’-tetramethyl-p-phenylene diamine) donors D connected via two Mo0 HiPoPS to a central TTP acceptor unit A. The three involved teams offer complementary expertise in polypyridine ligand and metal complex design, isocyanide chelates, and computational tailoring of long-lived MLCT excited states in 4d6 metal complexes. The three involved teams share complementary backgrounds and expertise in photoinduced electron transfer reactivity, encompassing bioinspired coupled electron and proton transfer, theoretical aspects of excited-state charge transfer processes, and light-driven charge accumulation in molecular systems.