具有双重光反应性的新型Ru（II）配合物：配体交换和<sup>1</sup> O <sub>2</sub>生成,Accounts of Chemical Research

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具有双重光反应性的新型Ru（II）配合物：配体交换和¹ O ₂生成
Accounts of Chemical Research ( IF 16.4 ) Pub Date : 2015-07-17 00:00:00 , DOI: 10.1021/acs.accounts.5b00227
Jessica D. Knoll ₁ , Bryan A. Albani ₁ , Claudia Turro ₁

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在设计用于所需光化学反应的新化合物时，揭示控制Ru（II）-聚吡啶基配合物电子结构的因素至关重要，本文讨论了调节激发态以进行配体解离和¹ O ₂产生的策略。光诱导配体解离的普遍接受的机制提出，解离三重态配体场（³ LF）状态的种群是通过振动冷却的三重态金属到配体电荷转移（³ MLCT）态的热种群进行的。然而，依赖温度的发射光谱使用[Ru（bpy）₂（L）₂的发射和配体交换量子产率提供了不同的活化能。] ²⁺（bpy ＝ 2，2′-联吡啶； L ＝ CH ₃ CN或py）。这表明的，人口³从振动激发态LF前进³ MLCT状态。因为腈的配体解离的量子产率比py的要高得多，所以将空间体积引入配体集中以扭曲伪八面体的几何形状并降低³ LF态的能量。一系列[Ru（tpy）（NN）（py）] ²⁺配合物（tpy = 2,2'：6'，2''-terpyridine; NN = bpy，6，在500 nm辐射下的py解离量子产率6'-二甲基-2,2'-联吡啶（ME ₂ BPY），2,2'-联喹啉（BIQ））通过增加2-3个数量级与该立体体积大的我₂相对于bpy的bpy和biq配体。超快瞬态吸收光谱显示当NN很大时³ LF态的填充量在3–7 ps内，并且密度泛函理论计算支持稳定的³ LF态。通过仔细选择配体组以调节激发态动力学，可以实现通过配体解离和¹ O ₂产生的双重活性。将扩展的π系统并入Ru（II）络合物，例如[Ru（bpy）（dppn）（CH ₃ CN）₂ ] ²⁺（dppn =苯并[ i ]双吡啶[3,2- a：2'，3 ′ -c ]吩嗪）和[Ru（tpy）（Me ₂ dppn）（py）] ²⁺（ME ₂ dppn = 3,6-二甲基苯并[我]吡啶并[3,2-一个：2'，3'- Ç ]吩嗪）引入了低洼，长寿命dppn / Me的₂ dppn ^3个ππ*激发态即产生¹ O ₂。与[Ru（bpy）₂（CH ₃ CN）₂ ] ²⁺相似，尽管[Ru（bpy）（dppn）（CH ₃ CN）₂ ] ²⁺照射会发生CH ₃ CN的光解离，但效率较低，因为的存在³ ππ*状态。[Ru（tpy）（Me ₂dppn）（py）] ²⁺对于促进光诱导的py离解至关重要，因为类似的复合物[Ru（tpy）（dppn）（py）] ²⁺产生¹ O _2的效率接近单位。调节激发态相对能量的能力提供了一种设计可能用于光化学疗法的更具活性的药物的方法，因为药物的光释放可以与活性氧的治疗作用耦合，通过两种不同的机制影响细胞死亡。有关调整激发态性质的经验教训可用于Ru（II）-聚吡啶基化合物在各种应用中的使用，例如太阳能转换，传感器和开关以及分子机器。

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New Ru(II) Complexes for Dual Photoreactivity: Ligand Exchange and 1O2 Generation

Uncovering the factors that govern the electronic structure of Ru(II)–polypyridyl complexes is critical in designing new compounds for desired photochemical reactions, and strategies to tune excited states for ligand dissociation and ¹O₂ production are discussed herein. The generally accepted mechanism for photoinduced ligand dissociation proposes that population of the dissociative triplet ligand field (³LF) state proceeds through thermal population from the vibrationally cooled triplet metal-to-ligand charge transfer (³MLCT) state; however, temperature-dependent emission spectroscopy provides varied activation energies using the emission and ligand exchange quantum yields for [Ru(bpy)₂(L)₂]²⁺ (bpy = 2,2′-bipyridine; L = CH₃CN or py). This suggests that population of the ³LF state proceeds from the vibrationally excited ³MLCT state. Because the quantum yield of ligand dissociation for nitriles is much more efficient than that for py, steric bulk was introduced into the ligand set to distort the pseudo-octahedral geometry and lower the energy of the ³LF state. The py dissociation quantum yield with 500 nm irradiation in a series of [Ru(tpy)(NN)(py)]²⁺ complexes (tpy = 2,2′:6′,2″-terpyridine; NN = bpy, 6,6′-dimethyl-2,2′-bipyridine (Me₂bpy), 2,2′-biquinoline (biq)) increases by 2–3 orders of magnitude with the sterically bulky Me₂bpy and biq ligands relative to bpy. Ultrafast transient absorption spectroscopy reveals population of the ³LF state within 3–7 ps when NN is bulky, and density functional theory calculations support stabilized ³LF states. Dual activity via ligand dissociation and ¹O₂ production can be achieved by careful selection of the ligand set to tune the excited-state dynamics. Incorporation of an extended π system in Ru(II) complexes such as [Ru(bpy)(dppn)(CH₃CN)₂]²⁺ (dppn = benzo[i]dipyrido[3,2-a:2′,3′-c]phenazine) and [Ru(tpy)(Me₂dppn)(py)]²⁺ (Me₂dppn = 3,6-dimethylbenzo[i]dipyrido[3,2-a:2′,3′-c]phenazine) introduces low-lying, long-lived dppn/Me₂dppn ³ππ* excited states that generate ¹O₂. Similar to [Ru(bpy)₂(CH₃CN)₂]²⁺, photodissociation of CH₃CN occurs upon irradiation of [Ru(bpy)(dppn)(CH₃CN)₂]²⁺, although with lower efficiency because of the presence of the ³ππ* state. The steric bulk in [Ru(tpy)(Me₂dppn)(py)]²⁺ is critical in facilitating the photoinduced py dissociation, as the analogous complex [Ru(tpy)(dppn)(py)]²⁺ produces ¹O₂ with near-unit efficiency. The ability to tune the relative energies of the excited states provides a means to design potentially more active drugs for photochemotherapy because the photorelease of drugs can be coupled to the therapeutic action of reactive oxygen species, effecting cell death via two different mechanisms. The lessons learned about tuning of the excited-state properties can be applied to the use of Ru(II)–polypyridyl compounds in a variety of applications, such as solar energy conversion, sensors and switches, and molecular machines.

更新日期：2015-07-17

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