Essential Role of the Ancillary Ligand in the Color Tuning of Iridium Tetrazolate Complexes

We report on the synthesis and physical chemical characterization of a class of heteroleptic mononuclear cyclometalated bis(phenylpyridine)iridium(III) complexes with tetrazolate chelate ligands, such as the deprotonated form of 2-(1H-tetrazol-5-yl)pyridine (PyTzH), 2-(1H-tetrazol-5-yl)pyrazine (PzTzH), and 5-bromo-2-(1H-tetrazol-5-yl)pyridine (BrPyTzH). The electrochemical and photophysical investigations of the resulting iridium(III) complexes revealed a rather wide span of redox and emission properties as a consequence of the nature of the ancillary tetrazolate ligand. In particular, within a series of the three neutral species, the emission observed changes from the blue-green of the pyridyltetrazolate complex to the red of that containing the pyrazinyltetrazolate ligand. The bromo-containing species, despite it displaying poor photophysical performances, is a synthetically attractive building block for the construction of polymetallic architectures. Moreover, the investigation of the reactivity toward electrophiles of one of the neutral mononuclear complexes, by methylation of the coordinated tetrazolate ligand, has also allowed further tuning of the electronic properties. In the latter case, the emission color tuning is also associated with a simple method for the conversion of a neutral species, a potentially triplet emitter for organic light-emitting devices, into the corresponding methylated cation, which might be used as a dopant for light-emitting electrochemical cell type devices or as a marker for biological labeling.

本工作报道了一类含四唑螯合配体的异配单核环金属化双(苯基吡啶)合铱(III)配合物的合成与物理化学表征，所选用的四唑配体包括2-(1H-四唑-5-基)吡啶（PyTzH）、2-(1H-四唑-5-基)吡嗪（PzTzH）以及5-溴-2-(1H-四唑-5-基)吡啶（BrPyTzH）的去质子化形式。对所得到的铱(III)配合物开展的电化学与光物理研究表明，由于辅助四唑配体的结构差异，该系列配合物展现出跨度较广的氧化还原与发光特性。具体而言，在该三种中性配合物的系列中，观测到的发光颜色从吡啶基四唑类配合物的蓝绿色，转变为含吡嗪基四唑配体的配合物的红色。含溴的配合物尽管光物理性能欠佳，但仍是构建多金属结构的极具合成价值的构筑单元。此外，通过对其中一种单核中性配合物的配位四唑配体进行甲基化，研究其亲电反应性的工作，还实现了对配合物电子特性的进一步调控。在后述案例中，发光颜色调控还关联了一种简便的转化方法：将可作为有机发光器件潜在三线态发光体的中性物种，转化为对应的甲基化阳离子。该阳离子可作为发光电化学电池类器件的掺杂剂，或用作生物标记探针。