A series of mono- and dinuclear Ru complexes containing a bridging ligand, L-diimide-L (L = 2-(2-pyridyl)benzimidazole; diimide = benzene-1,2:4,5-bis(dicarboximide) (bdi; pyromellitimide) or naphthalene-1,8:4,5-bis(dicarboximide) (ndi), with either propane or xylene group as linkers, have been prepared. The mono- and dinuclear Ru complexes containing the bdi or ndi ligand, exhibit characteristic metal-to-ligand charge transfer (MLCT) transition at 458 nm. The mono- and dinuclear Ru/Os complexes exhibit a rich redox chemistry arising from both M(II) to M(III) oxidation and ligand-based consecutive reduction of diimide and 2,2'-bipyridine (bpy) ligands. The emission decays fit well with double- or triple-exponential decay models. The non-exponential decay curve reveals the existence of several conformers in solution due to the flexible propane or p-xylene linker. The much shorter emission lifetimes of the [M(bpy)2(L-diimide-L)] complexes compared with the parent [M(bpy)2L] indicates the intramolecular electron-transfer from the excited M(bpy)2 moiety to the diimide. The fastest rates of electron transfer (3 · 1010 s-1) are attributable to the folded conformers suitable for the electron donor/acceptor through-space interaction. A time-resolved absorption spectroscopic study of the dinuclear bdi and ndi complexes revealed appearance of the electron-transfer products, M(III) and the diimide radical anion, and their rapid disappearance. The effect of the linkers of the ligand L-diimide-L on the rates of electron transfer and the back electron transfer is also discussed.
一系列含有桥联配体的单核和双核钌配合物已经制备,其中L-二亚胺-L(L = 2-(2-吡啶基)苯并咪唑;二亚胺 = 苯-1,2:4,5-双(二羧酰亚胺)(bdi;吡罗酰亚胺)或萘-1,8:4,5-双(二羧酰亚胺)(ndi),以丙烷或二甲苯基团作为连接剂。含有bdi或ndi配体的单核和双核钌配合物,在458纳米处表现出特征性的金属-配体电荷转移(MLCT)跃迁。单核和双核钌/钌复合物表现出丰富的氧化还原化学性质,既来自M(II)到M(III)氧化,又来自二亚胺和2,2'-联吡啶(bpy)配体的连续还原。发射衰减与双指数或三指数衰减模型很好地吻合。非指数衰减曲线揭示了溶液中存在多种构象异构体的存在,这是由于柔性的丙烷或p-二甲苯连接剂。与母体[M(bpy)2L]相比,[M(bpy)2(L-二亚胺-L)]配合物的发射寿命大大缩短,表明了从激发的M(bpy)2基团到二亚胺的分子内电子转移。最快的电子转移速率(3·1010 s-1)可归因于适合通过空间进行电子给体/受体相互作用的折叠构象异构体。双核bdi和ndi配合物的时间分辨吸收光谱研究揭示了电子转移产物M(III)和二亚胺自由基离子的出现,以及它们的快速消失。还讨论了配体L-二亚胺-L的连接剂对电子转移速率和反向电子转移的影响。