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Ruthenium(II) dendrimers containing carbazole-based chromophores as branches

机译：含有咔唑基发色团的钌（II）树状大分子

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Three new luminescent and redox-active Ru(II) complexes containing novel dendritic polypyridine ligands have been synthesized, and their absorption spectra, luminescence properties (both at room temperature in fluid solution and at 77 K in rigid matrix), and redox behavior have been investigated. The dendritic ligands are made of 1,10-phenanthroline coordinating subunits and of carbazole groups as branching sites, The first and second generation species of this novel class of dendritic ligands (L1 and L2, respectively; see Figure 1 for their structural formulas) have been prepared and employed. The metal dendrimers investigated are [Ru(bpy)(2)(L1)](2+) (1; bpy = 2,2'-bipyridine), [Ru(bpy)(2)(L2)](2+) (2), and [Ru(L1)(3)](2+) (3; see Figure 2). For the Sake of completeness and comparison purposes, also the absorption spectra, redox behavior, and luminescence properties of L1 and L2 have been studied, together with the properties of 3,6-di(tert-butyl)carbazole (L0) and [Ru(bpy)2(phen)]2+ (4, phen = 1, 10-phenanthroline). The absorption spectra of the free dendritic ligands show features which can be assigned to the various subunits (i.e., carbazole and phenanthroline groups) and additional bands at lower energies (at lambda > 300 nm) which are assigned to carbazole-to-phenanthroline charge-transfer (CT) transitions. These latter bands are significantly red-shifted upon acid and/or zinc acetate addition. Both L1 and L2 exhibit relatively intense luminescence at room temperature in fluid solution (lifetimes in the nanosecond time scale, quantum yields of the order of 10(-2)-10(-1)) and at 77 K in rigid matrix (lifetimes in the millisecond time scale). Such a luminescence is assigned to CT states at room temperature and to phenanthroline-centered pi-pi* triplet levels at 77 K. The room-temperature luminescence of L1 and L2 is totally quenched by acid or zinc acetate. The metal dendrimers exhibit the typical absorption and luminescence properties of Ru(II) polypyridine complexes. In particular, metal-to-ligand charge-transfer (MLCT) bands dominate the visible absorption spectra, and formally triplet MLCT levels govern the excited-state properties. Excitation spectroscopy evidences that all the light absorbed by the dendritic branches is transferred with unitary efficiency to the luminescent MLCT states in 1-3, showing that the new metal dendrimers can be regarded as efficient light-harvesting antenna systems. All the free ligands and metal dendrimers exhibit a rich redox behavior (except L2 and 3, whose redox behavior was not investigated because of solubility reasons), with clearly attributable reversible carbazole- and metal-centered oxidation and polypyridine-centered reduction processes. The electronic interaction between the carbazole redox-active sites of the dendritic ligands is affected by Ru(I I) coordination.
机译：合成了三种含有新型树突状聚吡啶配体的发光和氧化还原活性Ru（II）配合物，并已获得了它们的吸收光谱，发光特性（在室温下在液体溶液中和在77 K在刚性基质中）以及氧化还原行为。调查。树枝状配体由1,10-菲咯啉配位亚基和咔唑基团作为支链位点。这类新型树枝状配体的第一代和第二代物种（分别为L1和L2；其结构式见图1）具有准备和雇用。研究的金属树状聚合物为[Ru（bpy）（2）（L1）]（2+）（1; bpy = 2,2'-联吡啶），[Ru（bpy）（2）（L2）]（2+） （2）和[Ru（L1）（3）]（2+）（3；见图2）。为了完整和比较起见，还研究了L1和L2的吸收光谱，氧化还原行为和发光性质，以及3,6-二（叔丁基）咔唑（L0）和[Ru]的性质。 （bpy）2（phen）] 2+（4，phen = 1，10-菲咯啉）。游离树突状配体的吸收光谱显示出可以分配给各个亚基（即咔唑和菲咯啉基团）的特征，以及较低能量（λ> 300 nm）的附加谱带，它们被赋予咔唑-菲咯啉电荷-转换（CT）转换。在添加酸和/或乙酸锌后，这些后面的带显着红移。 L1和L2均在室温下在流体溶液中表现出相对强烈的发光（寿命以纳秒为时间尺度，量子产率为10（-2）-10（-1）数量级），在刚性基质中的发光强度为77 K（在毫秒时间标度）。此类发光在室温下被分配给CT状态，并在77 K时分配给以菲咯啉为中心的pi-pi *三重态水平。L1和L2的室温发光完全被酸或乙酸锌淬灭。金属树状聚合物表现出Ru（II）聚吡啶配合物的典型吸收和发光特性。特别是，金属到配体的电荷转移（MLCT）带支配了可见光吸收光谱，并且正式的三重态MLCT能级控制着激发态的性质。激发光谱法证明，树枝状树枝吸收的所有光均以单一效率转移至1-3中的发光MLCT状态，这表明新的金属树枝状聚合物可被视为高效的光收集天线系统。所有的游离配体和金属树枝状聚合物均表现出丰富的氧化还原行为（L2和3除外，由于溶解性原因未对它们的氧化还原行为进行研究），并且明显可归因于以咔唑和金属为中心的氧化反应和以聚吡啶为中心的还原过程。树枝状配体的咔唑氧化还原活性位点之间的电子相互作用受Ru（II）配位的影响。

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