Shavaleev Nail M, Bell Zöe R, Easun Timothy L, Rutkaite Ramune, Swanson Linda, Ward Michael D
School of Chemistry, University of Bristol, UK.
Dalton Trans. 2004 Nov 7(21):3678-88. doi: 10.1039/B411341A. Epub 2004 Oct 6.
N,N'-Chelating ligands based on the 2-(2-pyridyl)benzimidazole (PB) core have been prepared with a range of substituents (phenyl, pentafluorophenyl, naphthyl, anthracenyl, pyrenyl) connected to the periphery via alkylation of the benzimidazolyl unit at one of the N atoms. These PB ligands have been used to prepare a series of complexes of the type [Re(PB)(CO)(3)Cl], [Pt(PB)(CCR)(2)](where -CCR is an acetylide ligand) and [Ru(bpy)(2)(PB)]PF(6)(bpy = 2,2'-bipyridine). Six of the complexes have been structurally characterised. Electrochemical and luminescence studies show that all three series of complexes behave in a similar manner to the analogous complexes with 2,2'-bipyridine in place of PB. In particular, all three series of complexes show luminescence in the range 553-605 nm (Pt series), 620-640 nm (Re series) and 626-645 nm (Ru series) arising from the (3)MLCT state, with members of the Pt(II) series being the most strongly emissive with lifetimes of up to 500 ns and quantum yields of up to 6% in air-saturated CH(2)Cl(2) at room temperature. In the Re and Ru series there was clear evidence for inter-component energy-transfer processes in both directions between the (3)MLCT state of the metal centre and the singlet and triplet states of the pendant organic luminophores (naphthalene, pyrene, anthracene). For example the pyrene singlet is almost completely quenched by energy transfer to a Re-based MLCT excited state, which in turn is completely quenched by energy transfer to the lower-lying pyrene triplet state. For the analogous Ru(II) complexes the inter-component energy transfer is less effective, with (1)anthracene --> Ru((3)MLCT) energy transfer being absent, and Ru((3)MLCT)-->(3)anthracene energy transfer being incomplete. This is rationalised on the basis of a greater effective distance for energy transfer in the Ru(II) series, because the MLCT excited states are localised on the bpy ligands which are remote from the pendant aromatic group; in the Re series in contrast, the MLCT excited states involve the PB ligand to which the pendant aromatic group is directly attached, giving more efficient energy transfer.
基于2-(2-吡啶基)苯并咪唑(PB)核心的N,N'-螯合配体已通过在苯并咪唑基单元的一个N原子上进行烷基化反应，制备了一系列连接到外围的取代基(苯基、五氟苯基、萘基、蒽基、芘基)。这些PB配体已用于制备一系列类型为[Re(PB)(CO)₃Cl]、Pt(PB)(CCR)₂和[Ru(bpy)₂(PB)][PF₆]₂(bpy = 2,2'-联吡啶)的配合物。其中六种配合物已进行了结构表征。电化学和发光研究表明，所有这三个系列的配合物的行为与用2,2'-联吡啶代替PB的类似配合物相似。特别是，所有这三个系列的配合物在553 - 605nm(铂系列)、620 - 640nm(铼系列)和626 - 645nm(钌系列)范围内均有发光，这源于³MLCT态，铂(II)系列的成员发光最强，在室温下空气饱和的二氯甲烷中寿命可达500ns，量子产率可达6%。在铼和钌系列中，有明确证据表明在金属中心的³MLCT态与侧链有机发光体(萘、芘、蒽)的单重态和三重态之间存在双向的组分间能量转移过程。例如，芘单重态几乎完全通过能量转移到基于铼的MLCT激发态而被猝灭，而该激发态又通过能量转移到能量较低的芘三重态而完全被猝灭。对于类似的钌(II)配合物，组分间能量转移效率较低，不存在¹蒽→Ru(³MLCT)能量转移，且Ru(³MLCT)→³蒽能量转移不完全。这是基于钌(II)系列中能量转移的有效距离更大来解释的，因为MLCT激发态定域在远离侧链芳香基团的联吡啶配体上；相比之下，在铼系列中，MLCT激发态涉及直接连接侧链芳香基团的PB配体，从而实现了更有效的能量转移。
