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基本反应步骤，在将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清楚了，但多电子的转移和积累仍然具有极大的挑战性。人工光合作用关键依赖于多电子转移反应，因为低能量输入分子向高能产物的转化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积累多种氧化还原当量的新概念，以揭示其基本操作原理。我们计划在概念上取得三项关键进展：(1)我们将使用由丰富的过渡金属制成的新型光敏剂，其还原能力高于知名的贵金属光敏剂；(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势反转的概念，促进光驱动积累氧化还原当量；(3)我们将使用最先进的双脉冲双色泵浦-探测UV-Vis吸收光谱来监测多个电子的连续转移。第一个项目阶段将在计算化学的指导下，专注于基于钼(0)络合物的高电势光敏剂(HiPoPS)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)二元化合物的合成、光化学表征和理论理解，其中具有能够存储多达两个电子的受体，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执行。同时，第二个项目阶段将开发和探索具有氧化还原电位反转功能的新型电子受体。新的受体(TTP；4，5，9，10-四硫代芘和TBP，[1，1’：4’，1’’-terphenyl]-2，2’，2’’，5’-bis(dithiin)))将能够积累和存储最多四个氧化还原当量，它们将与两个得到PS-A-PS三联体的HiPoPS单元共价连接。第三个项目阶段的目标是由两个外围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的完全集成(全共价)分子五元组D-PS-A-PS-D。参与的三个团队在多吡啶配体和金属络合物设计、异氰化物螯合物以及计算剪裁4D6金属络合物中长寿命MLCT激发态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，以及分子系统中的光驱动电荷积累。

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.