1P2P_EnT - Efficient one-photon (1P) and novel two-photon (2P) mechanisms in light-driven energy transfer (EnT) catalysis

近年来，可见光在光化学中的应用引起了越来越多的关注，这主要是因为利用太阳光或高效LED作为能量输入的可能性以及由此产生的温和的反应条件。具有三重关键中间体的能量转移光催化是这一领域最有前途的发展方向之一。在之前几个能量转移步骤的机理研究的基础上，我们的目标是开发新的概念来提高反应量子产率(A)，并研究连续双光子吸收序列的机理(B)。后者将为新的底物激活铺平道路，而不需要“有害的”紫外线。在该项目中，将有意义的光谱技术与制备性和机械性辐照实验相结合，应有助于克服固有的困难，从而为新的机械性发现及其应用于实验室规模的过程铺平道路。这个项目的第一部分(A)涉及有效的能量转移序列。库仑相互作用和三重态继电器的使用将加快关键步骤的反应速度，并对光催化反应的产物产率产生积极的影响。第二部分(B)集中于在可见光双光子激发下产生的高激发三重态TN，用于建立不可预见的能量转移反应。底物活化的量子产率将通过胶束中催化剂-底物的预组织以及利用项目第一部分的发现(库仑相互作用和具有特别长TN寿命的三重态继电器)来控制。这些研究有助于深入了解有效利用TN状态作为催化活性物种的关键因素。该项目的预期成果将有助于开发更可持续的光化学反应，因为(I)通过开发新的概念将提高光能转换效率，以及(Ii)在异常温和的条件下激活惰性底物将是可行的。

Photochemical applications with visible light have attracted increasing attention in recent years, which is mainly due to the possibility of using sunlight or efficient LEDs as energy input and the resulting mild reaction conditions. Energy transfer photocatalysis with triplet key intermediates is among the most promising developments in this field. Building on several prior mechanistic studies with energy transfer steps, we are aiming to develop novel concepts to increase reaction quantum yields (A), and to investigate mechanisms with consecutive two-photon absorption sequences (B). The latter will pave the way for novel substrate activations without the need for “harmful” UV light. Within this project, the combination of meaningful spectroscopic techniques with preparative as well as mechanistic irradiation experiments should facilitate overcoming inherent difficulties, thereby paving the way for novel mechanistic findings and their applications to lab-scale processes. The first part of this project (A) is concerned with efficient energy transfer sequences. Coulomb interactions and the usage of triplet relays will accelerate reaction rates of key steps and positively affect product yields of photocatalytic reactions. The second part (B) focuses on higher excited triplet states Tn produced upon visible two-photon excitation for the establishment of unforeseen energy transfer reactivities. The quantum yields of substrate activation will be controlled by catalyst-substrate preorganization in micelles and by exploiting the findings from the first part of the project (Coulomb interactions and triplet relays with particularly long Tn lifetimes). These investigations could bring about a deep understanding of the key factors for the efficient usage of Tn states as catalytically active species. The anticipated results of this project will contribute to the development of more sustainable photochemical reactions, because (i) the light-to-energy conversion efficiencies will be increased by developing novel concepts and (ii) the activation of inert substrates will be feasible under unusually mild conditions.