Liu Zhiwei, Nie Daobo, Bian Zuqiang, Chen Fangfang, Lou Bin, Bian Jiang, Huang Chunhui
Beijing National Laboratory for Molecular Sciences (BNLMS), State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, P.R. China.
Chemphyschem. 2008 Mar 14;9(4):634-40. doi: 10.1002/cphc.200700648.
Twelve iridium complexes with general formula of Ir(C;N)(2)(LX) [C;N represents the cyclometalated ligand, i.e. 2-(2,4-difluorophenyl) pyridine (dfppy), 2-phenylpyridine (ppy), dibenzo{f, h}quinoxaline (DBQ); LX stands for beta-diketonate, i.e. acetyl acetonate (acac), 1-(carbazol-9-yl)-5,5-dimethylhexane-2,4-diketonate (CBDK), 1-(carbazol-9-yl)-5,5,6,6,7,7,7-heptafluoroheptane-2,4-diketonate (CHFDK), 1-(N-ethyl-carbazol-3-yl)-4,4,5,5,6,6,6-heptafluorohexane-1,3-diketonate (ECHFDK)] are synthesized, characterized and their photophysical properties are systemically studied. In addition, crystals of Ir(DBQ)(2)(CHFDK) and Ir(DBQ)(2)(acac) are obtained and characterized by single crystal X-ray diffraction. The choice of these iridium complexes provides an opportunity for tracing the effect of the triplet energy level of ancillary ligands on the photophysical and electrochemical behaviors. Data show that if the triplet energy level of the beta-diketonate is higher than that of the Ir(C;N)(2) fragment and there is no superposition on the state density map, strong (3)LC or (3)MLCT-based phosphorescence can be obtained. Alternatively, if the state density map of the two parts are in superposition, the (3)LC or (3)MLCT-based transition will be quenched at room temperature. Density functional theory calculations show that these complexes can be divided into two categories. The lowest excited state is mainly determined by C;N but not beta-diketonate when the difference between the triplet energy levels of the two parts is large. However, when this difference is very small, the lowest excited state will be determined by both sides. This provides a satisfactory explanation for the experimental observations.
合成了十二个通式为Ir(C^N)(2)(LX)的铱配合物[C^N代表环金属化配体，即2-(2,4-二氟苯基)吡啶(dfppy)、2-苯基吡啶(ppy)、二苯并{f, h}喹喔啉(DBQ)；LX代表β-二酮，即乙酰丙酮(acac)、1-(咔唑-9-基)-5,5-二甲基己烷-2,4-二酮(CBDK)、1-(咔唑-9-基)-5,5,6,6,7,7,7-七氟庚烷-2,4-二酮(CHFDK)、1-(N-乙基-咔唑-3-基)-4,4,5,5,6,6,6-七氟己烷-1,3-二酮(ECHFDK)]，对其进行了表征，并系统研究了它们的光物理性质。此外，获得了Ir(DBQ)(2)(CHFDK)和Ir(DBQ)(2)(acac)的晶体，并通过单晶X射线衍射对其进行了表征。这些铱配合物的选择为追踪辅助配体的三重态能级对光物理和电化学行为的影响提供了一个机会。数据表明，如果β-二酮的三重态能级高于Ir(C^N)(2)片段的三重态能级，并且在态密度图上没有叠加，则可以获得强的基于(3)LC或(3)MLCT的磷光。或者，如果两部分的态密度图叠加，则基于(3)LC或(3)MLCT的跃迁在室温下将被淬灭。密度泛函理论计算表明，这些配合物可分为两类。当两部分的三重态能级差异较大时，最低激发态主要由C^N而非β-二酮决定。然而，当这种差异非常小时，最低激发态将由两侧共同决定。这为实验观察提供了令人满意的解释。
