Aryl radical anions: key intermediates on the route to sustainable green-light ionizations

水相光电离产生水合电子，已经成功地用于卤化有机废物的还原解毒和直接还原氮或二氧化碳；然而，所有这些过程都必须依赖UV-C光(&lt；254 nm)来产生电子。我们的建议涉及只需要绿光(532 Nm)的光电离，并且基于催化循环，因此只消耗生物可用的牺牲供体。从我们最近发表的关于Ru-三(联吡啶)正离子(第一个完全绿光驱动的循环光致电离的例子，但量子产率非常低)和萘自由基阴离子(它显示出迄今为止不稳定中间体的绿光电离的最高量子产率，但不能在绿光下产生)的探索性研究开始，我们打算在胶束环境中通过结合这两种方法来完成这一任务。为此，Ru化合物将作为捕光化合物，以及具有更多环的芳烃，例如，芘衍生物，作为氧化还原催化剂。通过绿光激发的Ru络合物的能量转移和牺牲供体抗坏血酸的电子转移，我们将第一个光子的能量存储在芳基自由基阴离子中，然后我们将其与第二个绿色光子电离，在此过程中恢复氧化还原催化剂。胶束的功能是通过非共价相互作用确保反应序列的预期顺序并抑制副反应。我们预计芳基自由基阴离子将表现出良好的光电离性能，因为它们的刚性分子骨架应该减缓其激发态的无辐射失活，这与电子抛射竞争，并且它们的高能量含量导致高过剩的电子形成能量。通过双脉冲激光闪光光解电子产额的强度依赖测量，以及激发态自由基阴离子的寿命测量，我们打算定量地研究这两种影响。正如我们所期望的那样，这一项目一方面将使我们能够以尽可能高的效率获得完全绿光驱动的电子源，另一方面将为揭示影响光致电离量子产额的因素提供重要的新见解。

Aqueous photoionizations produce hydrated electrons, which have already been successfully used for the reductive detoxification of halogenated organic waste and for the direct reduction of nitrogen or carbon dioxide; however, all these procedures had to rely on UV-C light (< 254 nm) for electron generation. Our proposal is concerned with photoionizations that require only green light (532 nm) and are based on catalytic cycles such that nothing but a bioavailable sacrificial donor is consumed.Starting from our very recently published exploratory investigations on the ruthenium-tris(bipyridyl) dication (the first example of a completely green-light driven cyclic photoionization, but with a very low quantum yield) and on the naphthalene radical anion (which exhibits the highest quantum yield known to date for the green-light ionization of an unstable intermediate, but cannot be generated with green light), we intend to fulfil that assignment by a combination of both approaches in a micellar environment. To that end, the ruthenium compound shall serve us as a light-harvesting compound and an arene with a larger number of rings, e.g., a pyrene derivative, as a redox catalyst. By an energy transfer from the green-light excited ruthenium complex followed by an electron transfer from the sacrificial donor ascorbate, we store the energy of the first photon in the aryl radical anion, which we then ionize with a second green photon, recovering the redox catalyst in that process. The function of the micelle is to ensure the desired order of the reaction sequence and to suppress side reactions, both through noncovalent interactions.We anticipate aryl radical anions to exhibit good photoionizability because their rigid molecular skeleton should decelerate the radiationless deactivation of their excited states, which competes with the electron ejection, and their high energy content results in a high excess energy of electron formation. Through intensity dependent measurements of the electron yields by two-pulse laser flash photolysis, together with lifetime measurements of the excited radical anions, we intend to study both effects quantitatively.As we expect, this project will allow us to procure completely green-light driven electron sources with as high an efficiency as possible on one hand, and on the other hand will provide important new insight into the factors that gouvern the quantum yields of photoionizations.