Zhu Xiaolin, Liu Bingqing, Cui Peng, Kilina Svetlana, Sun Wenfang
Department of Chemistry and Biochemistry, North Dakota State University, Fargo, North Dakota 58108-6050, United States.
Materials and Nanotechnology Program, North Dakota State University, Fargo, North Dakota 58108-6050, United States.
Inorg Chem. 2020 Dec 7;59(23):17096-17108. doi: 10.1021/acs.inorgchem.0c02366. Epub 2020 Nov 10.
Five mono/di/trinuclear iridium(III) complexes (-) bearing the carbazole-derivative-tethered 2-(quinolin-2-yl)quinoxaline (quqo) diimine (N^N) ligand were synthesized and characterized. The photophysical properties of these complexes and their corresponding diimine ligands were systematically studied via UV-vis absorption, emission, and transient absorption (TA) spectroscopy and simulated by time-dependent density functional theory. All complexes possessed strong well-resolved absorption bands at <400 nm that have predominant ligand-based π,π* transitions and broad structureless charge-transfer (CT) absorption bands at 400-700 nm. The energies or intensities of these CT bands varied pronouncedly when the number of tethered Ir(quqo)(piq) (piq refers to 1-phenylisoquinoline) units, π conjugation of the carbazole derivative linker, or attachment positions on the carbazole linker were altered. All complexes were emissive at room temperature, with - showing near-IR (NIR) MLCT (metal-to-ligand charge-transfer)/LLCT (ligand-to-ligand charge-transfer) emission at ∼710 nm and and exhibiting red or NIR ILCT (intraligand charge-transfer)/LMCT (ligand-to-metal charge-transfer) emission in CHCl. In CHCN, - displayed an additional emission band at ca. 590 nm (ILCT/LMCT/MLCT/π,π* in nature) in addition to the 710 nm band. The different natures of the emitting states of - versus those of and also gave rise to different spectral features in their triplet TA spectra. It appears that the parentage and characteristics of the lowest triplet excited states in these complexes are mainly impacted by the π systems of the bridging carbazole derivatives and essentially no interactions among the Ir(quqo)(piq) units. In addition, all of the diimine ligands tethered by the carbazole derivatives displayed a dramatic solvatochromic effect in their emission due to the predominant intramolecular charge-transfer nature of their emitting states. Aggregation-enhanced emission was also observed from the mixed CHCl/ethyl acetate or CHCl/hexane solutions of these ligands.
合成并表征了五种带有咔唑衍生物连接的2-(喹啉-2-基)喹喔啉(quqo)二亚胺(N^N)配体的单核/双核/三核铱(III)配合物(-)。通过紫外可见吸收、发射和瞬态吸收(TA)光谱系统研究了这些配合物及其相应二亚胺配体的光物理性质，并采用含时密度泛函理论进行了模拟。所有配合物在<400 nm处都有强且分辨良好的吸收带，主要是基于配体的π,π跃迁，在400 - 700 nm处有宽的无结构电荷转移(CT)吸收带。当连接的Ir(quqo)(piq)(piq指1-苯基异喹啉)单元数量、咔唑衍生物连接基的π共轭或咔唑连接基上的连接位置改变时，这些CT带的能量或强度有显著变化。所有配合物在室温下都有发射，其中-在~710 nm处显示近红外(NIR)金属到配体电荷转移(MLCT)/配体到配体电荷转移(LLCT)发射，而 和 在CHCl中呈现红色或近红外配体内电荷转移(ILCT)/配体到金属电荷转移(LMCT)发射。在CHCN中，-除了710 nm的谱带外，在约590 nm处还显示出一个额外的发射带(本质上是ILCT/LMCT/MLCT/π,π)。-与 和 的发射态性质不同，这也导致了它们三重态TA光谱中的不同光谱特征。这些配合物中最低三重激发态的起源和特征似乎主要受桥连咔唑衍生物的π体系影响，并且Ir(quqo)(piq)单元之间基本没有相互作用。此外，所有由咔唑衍生物连接的二亚胺配体由于其发射态主要是分子内电荷转移性质，在发射过程中表现出显著的溶剂化变色效应。从这些配体的CHCl/乙酸乙酯或CHCl/己烷混合溶液中也观察到了聚集增强发射。
