Morselli Giacomo, Eggenweiler Tim H, Villa Marco, Prescimone Alessandro, Wenger Oliver S
Department of Chemistry, University of Basel, St. Johanns-Ring 19, 4056 Basel, Switzerland.
Department of Chemistry "G. Ciamician", University of Bologna, Via Piero Gobetti 85, 40129 Bologna, Italy.
J Am Chem Soc. 2025 Aug 6;147(31):28226-28240. doi: 10.1021/jacs.5c08541. Epub 2025 Jul 28.
Photoactive Cr complexes are typically based on polypyridine coordination environments, exhibit red luminescence, and are good photo-oxidants but have modest photoreducing properties. We report new Cr complexes with anionic chelate ligands that enable color-tunable near-infrared luminescence and red-light-driven photoreduction reactions involving elementary steps that are endergonic up to 0.5 eV. Improving the metal-ligand bond covalency rather than more established approaches such as optimizing ligand field strength and coordination geometry is the underlying molecular design concept to achieve this favorable behavior. Our analysis suggests an intricate interplay between productive but slow endergonic photoinduced electron transfer and energy-wasting charge recombination rooted in cage escape effects, which could be generally important for photocatalysis. Our work also suggests the occurrence of doublet-doublet annihilation, a process that seems to have been largely neglected in current research on photoactive Cr complexes but which could provide a mechanistic entry point into the widely used process of photochemical upconversion, typically based on triplet-triplet annihilation. Overall, this work conceptually advances the current state of the art of photoactive Cr complexes in terms of molecular design, luminescence, and photoredox behavior. More generally, it informs photochemistry in terms of elucidating the limits of light-to-chemical energy conversion efficiency and the value of long-lived excited states in complexes of earth-abundant transition metals.
光活性铬配合物通常基于多吡啶配位环境，呈现红色发光，是良好的光氧化剂，但光还原性能一般。我们报道了一种新型铬配合物，其具有阴离子螯合配体，可实现颜色可调的近红外发光以及红光驱动的光还原反应，该反应涉及高达0.5电子伏特的吸热基元步骤。实现这种良好性能的潜在分子设计理念是提高金属 - 配体键的共价性，而非采用诸如优化配体场强度和配位几何结构等更为成熟的方法。我们的分析表明，在有效的但缓慢的吸热光致电子转移与源于笼逃逸效应的能量耗散电荷复合之间存在复杂的相互作用，这可能对光催化具有普遍重要性。我们的工作还表明存在双 - 双湮灭现象，这一过程在当前关于光活性铬配合物的研究中似乎很大程度上被忽视了，但它可能为通常基于三重态 - 三重态湮灭的广泛应用的光化学上转换过程提供一个机制切入点。总体而言，这项工作在分子设计、发光和光氧化还原行为方面从概念上推进了光活性铬配合物的当前技术水平。更广泛地说，它在阐明光到化学能转换效率的极限以及地球丰富的过渡金属配合物中长寿命激发态的价值方面为光化学提供了信息。
