Cyclometalated Ir(III) complexes showing strong absorption of visible light and a long-lived triplet state are of particular interest as photocatalysts and photosensitizers. Steady-state and femtosecond transient absorption spectroscopy, complemented with TD-DFT computations, are used to study the ultrafast intersystem crossing (ISC) dynamics of two perylenebisimide (PBI)-containing cyclometalated Ir(III) complexes (Ir–PBI and Ir–NPBI). The S₁ → T_n ISC dynamics of these complexes is ultrafast, similar to the conventional Ir(III) complexes bearing a ¹MLCT → ³MLCT transition. Much longer triplet decay lifetimes are observed in Ir–PBI (τ_T = 11.4 μs) and Ir–NPBI (τ_T = 7.9 μs) compared to conventional Ir(III) complexes (τ_T < 5 μs). This can be rationalized by the character of the lowest-energy triplet excited state (T₁). In the case of the PBI-containing complexes, the T₁ is of intraligand character (³IL), and the T₁ → S₀ spin–orbital coupling (SOC) is 3 cm^–1. This is in contrast with conventional Ir(III) complexes, where the ³MLCT → S₀ has SOCs of 490 cm^–1. In the presence of a typical sacrificial electron donor, triethanolamine (TEOA), the coordinated PBI ligands are transformed into their radical form under an inert atmosphere, either with or without photoexcitation. We found that the triplet-state population is decreased with formation of the radical. The doublet excited state has a lifetime in the range of 4–7 ps.

中文翻译：

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环金属化的Ir（III）配合物Per双酰亚胺及其π自由基阴离子配体的超快激发态动力学

显示出对可见光的强吸收和长寿命的三重态的环金属化的Ir（III）配合物作为光催化剂和光敏剂特别受关注。稳态和飞秒瞬态吸收光谱，结合TD-DFT计算，用于研究两种含per二酰亚胺（PBI）的环金属化Ir（III）配合物（Ir–PBI和Ir–NPBI）的超快速系统间穿越（ISC）动力学）。这些配合物的S ₁ →T _n ISC动力学非常快，类似于带有¹ MLCT→ ³ MLCT跃迁的常规Ir（III）配合物。长得多的三线态寿命衰变在观察到的Ir-PBI（τ _Ť= 11.4微秒）和铱NPBI（τ _Ť相比于传统铱（III）配合物= 7.9微秒）（τ _Ť <5微秒）。这可以通过最低能量的三重态激发态（T ₁）的特性来合理化。对于含PBI的复合物，T ₁具有配体内特性（³ IL），T ₁ →S ₀自旋-轨道耦合（SOC）为3 cm ^–1。这与常规的Ir（III）配合物相反，后者的³ MLCT→S _0的SOC为490 cm ^–1。在典型的牺牲电子供体三乙醇胺（TEOA）的存在下，配位的PBI配体在惰性气氛下（无论有无光激发）都转变为自由基形式。我们发现三重态人口随着自由基的形成而减少。双峰激发态的寿命为4–7 ps。