长发光寿命且颜色可调的铑(III)过渡金属配合物的设计、合成与应用研究

Polypyridyl and cyclometalated rhodium(III) complexes, with the most common oxidation state of the second row rhodium metal, are considered as the closest congener of the related isoelectronic iridium(III) system. Although the polypyridyl and cyclometalated rhodium(III) and iridium(III) complexes share the similar synthetic methodology, structural characteristics, and some physical and chemical properties, the luminescence studies of rhodium(III) system have comparatively been much less explored. Despite a few examples of polypyridyl and cyclometalated rhodium(III) complexes showing luminescence at room temperature in solution known and most of them only showed weak luminescence with short lifetime, to the best of my knowledge, no detailed investigations of the luminescence properties with systematic variations of different ligands on the rhodium(III) system have been made in order to improve and enhance the luminescence behaviors, with stronger luminescence intensity and lifetime as well as a broader range of color tuning capability, for the potential applications. Upon coordination of rhodium(III) metal center by various ligands with lower-lying LC energy level and/or with strong -donating ability such as alkynyl, N-heterocyclic carbene, cyclometalated aryl, pyrazole anchoring group, it is anticipated that an improvement or enhancement of the luminescence behaviors of rhodium(III) system could be achieved. The nature of long luminescence lifetime is crucial for the use of time resolved detection in biophysical measurements and luminescence microscopy, while the search for ideal emissive dopants in OLEDs requires the broader range of luminescence color tuning capability. Thus the aim of this project is to design and synthesize novel classes of   rhodium(III) complexes, with hopefully, rich luminescence properties of long lifetime and color tunability. Their electronic absorption, luminescence and electrochemical behaviors will be explored. The present project may open up new avenues for the fundamental understanding of the photophysical and spectroscopic properties of rhodium(III) system, as well as to provide interesting new opportunities for the construction of molecular devices with tunable luminescence behavior and for the exploration of luminescent materials with improved and optimized properties, in the forms of energy, emission quantum yields and excited state lifetimes.

多吡啶环金属铑(III)配合物是与等电子的铱(III)配合物性质最相近的同系物。虽然存在少量的多吡啶环金属铑(III)配合物在室温溶液中能够发光，但其发光强度弱、发光时间短。铑(III)金属中心与不同的具有低LC能级的配体和/或强给电子能力的配体（如炔基、氮杂环卡宾、环金属芳基、吡唑基）配位后，可增强配合物的发光性能。通过时间分辨检测技术将配合物应用于生物物理测量与发光显微镜检测中，要求配合物具有长发光寿命性能；而作为有机电致发光器件中良好的发光掺杂剂的配合物则应具有宽范围的颜色可调控性能。因此，本项目致力于设计合成新型的具有长发光寿命、颜色可调的良好的发光性能的铑(III)系列配合物，详细系统地研究它们的电子吸收光谱、发光性、电化学性质等，将可能为构建发光性能可调控的分子器件和能量类型、发光量子效率和激发态寿命等性能更加优异的发光材料提供新途径。

多吡啶环金属铑(III)配合物是与等电子的铱(III)配合物性质最相近的同系物。虽然存在少量的多吡啶环金属铑(III)配合物在室温溶液中能够发光，但其发光强度弱、发光时间短。通过选择具有低位分子内 (IL) 激发态的强 σ 供体作为环金属化配体，可以提高金属铑(III)的 d-d 激发态并引入低位发射的 IL 激发态。本工作使用这种策略合成的铑（III）配合物，在薄膜中表现出良好的热稳定性和优异的发光量子产率 (Фlum≈ 0.65)，这使其成为很有前途的全新 OLED 发光材料。用这些配合物作为磷光掺杂剂来制备溶液处理法和真空沉积法，能制备含铑（III）配合物有机发光器件 (OLED)，这些OLED器件的外部量子效率（EQEs）最高可达 12.2%，工作半衰期在 100 cd m-2 时高达 17322 小时达到。通过引入香豆素发色团到辅助基团中，电中性的铑(III)配合物的纯蓝光发射得以实现，CIE色坐标x和y分别为0.15 和0.11，这也为铑（III）配合物实现全彩色发光提供了可能性。这项工作首次开发了铑（III）配合物在OLED器件中的应用研究，为OLED材料的多样化发展开辟了新途径，在国际上填补了铑金属用作荧光粉的空白，实现我国自主知识产权。这项研究成果也揭示了铑除了催化领域外，在OLED研发领域中的潜在应用的突破。