Exploiting the disulfide/dithiol switch in photoinduced proton coupled electron transfer reactions

与可持续能源方案相关的小分子转化，特别是太阳能燃料的产生，通常需要多个电子和质子的转移。因此，催化这些具有挑战性的惰性分子转化的催化剂必须协调复杂的多电子、多质子与底物之间的转移，即在生物系统中也广泛存在的质子耦合电子转移（PCET）事件。这些过程可以依次通过质子转移和电子转移（PT-ET）进行，反之亦然（ET-PT），或者电子和质子可以以协调一致的方式（CPET）转移，以避免任何可能具有高能量的带电中间体。由于它们从光激发态发生时固有的非平衡性质，由光驱动的PCET场景特别复杂，而且尚未得到很好的理解。然而，理解和控制多个光触发电荷转移过程的动力学将最终对改善阳光到燃料的转换和任何期望的太阳能燃料的能量存储至关重要。这个基础研究项目的目标是阐明光诱导PCET过程中的事件序列，使用在配体外围装饰有二硫/二硫醇开关的新型光激发金属配合物。提出的化学反应利用了二硫化物/二硫醇相互转化的2e−/2H+性质，以及在二硫化物部分首次还原后经常发生的潜在反转。在第一个资助期取得的进展的基础上，这个项目的关键问题涉及到精心设计的分子和超分子系统光激发后的单个化学步骤的舞蹈，包括ET， PT和S-S键的断裂。这些问题由一个跨学科的项目团队解决，并与优先计划的几个研究小组密切合作，使用一套实验和计算方法。概念指南和最终目标是在初始激发态PCET过程之后触发第二个ET事件，可能与PT耦合。这将为单次光激发事件引发的多电子/多质子化学开辟一条有希望的途径。

The transformation of small molecules relevant for sustainable energy scenarios, specifically the generation of solar fuels, usually requires the transfer of multiple electrons and protons. Catalysts mediating these challenging transformations of mostly inert molecules thus have to orchestrate the complex multielectron, multiproton transfer to/from the substrate, viz. the proton-coupled electron transfer (PCET) events that are also widespread in biological systems. These processes may proceed sequentially via proton transfer followed by electron transfer (PT-ET), or vice versa (ET-PT), or the electron and proton may be transferred in a concerted fashion (CPET) to avoid any charged intermediates of potentially high energy. Because of their inherent nonequilibrium nature when occurring from photoexcited states, PCET scenarios driven by light are particularly complex and not well understood. However, understanding and controlling the dynamics of multiple light-triggered charge transfer processes will ultimately be crucial for improved sunlight to fuel conversion and for any desired energy storage in solar fuels. This fundamental research project targets the elucidation of the sequence of events during photoinduced PCET processes using novel photoexcitable metal complexes that are decorated with a disulfide/dithiol switch in the ligand periphery. The proposed chemistry capitalizes on the 2e−/2H+ nature of the disulfide/dithiol interconversion and on the potential inversion that often occurs after the first reduction of a disulfide moiety. Building upon the progress achieved during the first funding period, key questions of this project concern the choreography of the individual chemical steps following photoexcitation of well-designed molecular and supramolecular systems, including ET, PT and the rupture of the S-S bond. These questions are addressed by an interdisciplinary project team and in close collaborations with several research groups of the priority program, using a suite of experimental and computational methods. The conceptual guideline, and the ultimate goal, is the triggering of a second ET event, potentially coupled to PT, following the initial excited state PCET process. This will open a promising entry towards multielectron/multiproton chemistry initiated by single photoexcitation event.