Cyclometalated and polypyridyl complexes of d₆ metals are promising photoredox catalysts, using light to drive reactions with high kinetic or thermodynamic barriers via the generation of reactive radical intermediates. However, while tuning of their redox potentials, absorption energy, excited-state lifetime and quantum yield are well-known criteria for modifying activity, other factors could be important. Here we show that dynamic ion-pair reorganization controls the reactivity of a photoredox catalyst, [Ir[dF(CF₃)ppy]₂(dtbpy)]X. Time-resolved dielectric-loss experiments show how counter-ion identity influences excited-state charge distribution, evincing large differences in both the ground- and excited-state dipole moment depending on whether X is a small associating anion (PF₆⁻) that forms a contact-ion pair versus a large one that either dissociates or forms a solvent-separated pair (BAr^F₄⁻). These differences correlate with the reactivity of the photocatalyst toward both reductive and oxidative electron transfer, amounting to a 4-fold change in selectivity toward oxidation versus reduction. These results suggest that ion pairing could be an underappreciated factor that modulates reactivity in ionic photoredox catalysts.

d ₆金属的环金属化和多吡啶基配合物是很有前途的光氧化还原催化剂，它利用光通过产生活性自由基中间体来驱动具有高动力学或热力学势垒的反应。然而，虽然调整它们的氧化还原电位、吸收能量、激发态寿命和量子产率是众所周知的改变活性的标准，但其他因素可能很重要。在这里，我们展示了动态离子对重组控制光氧化还原催化剂的反应性，[Ir[dF(CF ₃ )ppy] ₂(dtbpy)]X。时间分辨介电损耗实验表明反离子身份如何影响激发态电荷分布，证明基态和激发态偶极矩的巨大差异取决于 X 是否是形成的小缔合阴离子 (PF ₆ ^- )接触离子对与解离或形成溶剂分离对（BAr ^F ₄ ^-）的大离子对。这些差异与光催化剂对还原和氧化电子转移的反应性相关，相当于氧化与还原选择性的 4 倍变化。这些结果表明，离子对可能是调节离子光氧化还原催化剂反应性的一个被低估的因素。