Pfund Björn, Wenger Oliver S
Department of Chemistry, University of Basel, St. Johanns-Ring 19, 4056 Basel, Switzerland.
J Am Chem Soc. 2025 Jul 30;147(30):26477-26485. doi: 10.1021/jacs.5c06115. Epub 2025 Jul 17.
Nearly all photochemical transformations known to date follow Kasha's rule, implying that reactions occur only from the lowest electronically excited state of a given spin multiplicity due to the fast relaxation of higher-energy states. We challenge this foundational principle by demonstrating with time-resolved laser spectroscopy that the 4,4″-dicyano--terphenyl radical anion can undergo photoinduced electron transfer directly from a higher-energy excited state, enabling reactivity inaccessible to the lowest excited state with the same spin multiplicity. Preassociation with the substrate and driving-force optimization are critical for overcoming the kinetic barrier to subnanosecond electron transfer, enabling bimolecular anti-Kasha reactivity. This advance establishes a general and broadly applicable framework for bypassing one of the most fundamental principles of photophysics and photochemistry, Kasha's rule, and opens new possibilities in photoredox catalysis and solar energy conversion by rethinking the energetic and kinetic landscape.
迄今为止已知的几乎所有光化学转化都遵循卡沙规则，这意味着由于高能态的快速弛豫，反应仅从给定自旋多重性的最低电子激发态发生。我们通过时间分辨激光光谱证明4,4″-二氰基-对三联苯自由基阴离子可以直接从高能激发态进行光诱导电子转移，从而挑战了这一基本原理，使得具有相同自旋多重性的最低激发态无法实现的反应活性成为可能。与底物的预缔合和驱动力优化对于克服亚纳秒电子转移的动力学障碍至关重要，从而实现双分子反卡沙反应活性。这一进展建立了一个通用且广泛适用的框架，用于绕过光物理和光化学最基本的原理之一——卡沙规则，并通过重新思考能量和动力学格局，在光氧化还原催化和太阳能转换方面开辟了新的可能性。
