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

• Applicant: Professorin Dr. Katja Heinze
• Subject Area: Inorganic Molecular Chemistry - Synthesis and Characterisation ; Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry ; Theoretical Chemistry: Electronic Structure, Dynamics, Simulation
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 501188872

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.

• DFG Programme: Research Grants
• International Connection: France, Switzerland
• Partner Organisation: Agence Nationale de la Recherche / The French National Research Agency; Schweizerischer Nationalfonds (SNF)
• Cooperation Partners: Dr. Isabelle Dixon; Professor Dr. Oliver S. Wenger