Department of Chemistry, University of Sheffield, Sheffield S3 7HF, U.K.
Inorg Chem. 2011 Nov 21;50(22):11323-39. doi: 10.1021/ic2007759. Epub 2011 Oct 5.
An extensive series of blue-luminescent iridium(III) complexes has been prepared containing two phenylpyridine-type ligands and one ligand containing two pyrazolylpyridine units, of which one is bound to Ir(III) and the second is pendant. Attachment of {Ln(hfac)(3)} (Ln = Eu, Gd; hfac = anion of 1,1,1,5,5,5,-hexafluoropentanedione) to the second coordination site affords Ir(III)/Ln(III) dyads. Crystallographic analysis of several mononuclear iridium(III) complexes and one Ir(III)/Eu(III) dyad reveals that in most cases the complexes can adopt a folded conformation involving aromatic π stacking between a phenylpyridine ligand and the bis(pyrazolylpyridine) ligand, but in one series, based on CF(3)-substituted phenylpyridine ligands coordinated to Ir(III), the steric bulk of the CF(3) group prevents this and a quite different and more open conformation arises. Quantum mechanical calculations well reproduce these two types of "folded" and "open" conformations. In the Ir(III)/Eu(III) dyads, Ir → Eu energy transfer occurs with varying degrees of efficiency, resulting in partial quenching of the Ir(III)-based blue emission and the appearance of a sensitized red emission from Eu(III). Calculations based on consideration of spectroscopic overlap integrals rule out any significant contribution from Förster (dipole-dipole) energy transfer over the distances involved but indicate that Dexter-type (exchange) energy transfer is possible if there is a small electronic coupling that would arise, in part, through π stacking between components. In some cases, an initial photoinduced electron-transfer step could also contribute to Ir → Eu energy transfer, as shown by studies on isostructural iridium/gadolinium model complexes. A balance between the blue (Ir-based) and red (Eu-based) emission components can generate white light.
已经制备了一系列含有两个苯并吡啶型配体和一个含有两个吡唑并吡啶单元的配体的强蓝色发光铱(III)配合物，其中一个与 Ir(III)键合，第二个是悬垂的。将 {Ln(hfac)(3)}（Ln = Eu，Gd；hfac = 1,1,1,5,5,5,-五氟戊二酮的阴离子）连接到第二个配位位点上，得到 Ir(III)/Ln(III) 二聚体。对几种单核铱(III)配合物和一个 Ir(III)/Eu(III) 二聚体的晶体学分析表明，在大多数情况下，配合物可以采用折叠构象，涉及苯并吡啶配体和双（吡唑并吡啶）配体之间的芳香π堆积，但在一系列基于 CF3-取代的苯并吡啶配体与 Ir(III)配位的配合物中，CF3 基团的空间位阻阻止了这种情况的发生，产生了一种截然不同的、更开放的构象。量子力学计算很好地再现了这两种“折叠”和“开放”构象。在 Ir(III)/Eu(III) 二聚体中，Ir→Eu 能量转移发生在不同程度的效率，导致 Ir(III)基蓝色发射的部分猝灭和 Eu(III)敏化的红色发射的出现。基于考虑光谱重叠积分的计算排除了涉及的距离上 Förster（偶极-偶极）能量转移的任何显著贡献，但表明如果存在部分电子耦合，则 Dexter 型（交换）能量转移是可能的，这部分是通过组件之间的 π 堆积产生的。在某些情况下，如对同构铱/钆模型配合物的研究所示，初始光诱导电子转移步骤也可以有助于 Ir→Eu 能量转移。蓝色（基于 Ir）和红色（基于 Eu）发射成分之间的平衡可以产生白光。
