Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan 30013, Republic of China.
J Phys Chem A. 2010 Sep 30;114(38):10339-44. doi: 10.1021/jp102264q.
We investigated the relaxation dynamics of bis(2-phenylpyridinato-)(2,2'-bipyridine)iridium(III), Ir(ppy)(2)bpy using the technique of time-resolved spectroscopy. In the visible emission spectra this molecule exhibits triple phosphorescence: displaying blue, green, and orange bands. From the dependence of spectral shifts with polarity of solvent, decay lifetimes, and the results of calculations using time-dependent density functional theory, we assigned these three emitting states to be triplet interligand charge-transfer ((3)LLCT), metal-to-ligand ppy charge transfer ((3)MLCT(ppy)), and metal-to-ligand bpy charge transfer ((3)MLCT(bpy)) states. The blue states were formed promptly after excitation at wavelength 355 nm; the one lying at higher energy decaying with a time coefficient 0.79-2.56 ns is assigned to be a triplet MLCT, and the other at lower energy decaying in 1.5-2.8 μs is assigned to (3)LLCT(A), A symmetry. This decay time coefficient of (3)LLCT(A) decreases with increasing dielectric constant of the solvent indicating this state mixing of some MLCT character. The green state (3)MLCT(ppy) decays in 0.13-4.8 ns to a nearby intermediate state either (3)MLCT(ppy) or (3)MLCT(bpy). The orange state (3)MLCT(bpy) is coupled to the intermediate state to have a rise time about 0.36-0.84 ns and decays in 425-617 ns. Although many triplet states exist in a small energy range, they couple weakly to display triple emission. All (3)LLCT and (3)MCLT states are coupled to the singlet (1)LLCT manifold directly and/or indirectly and contribute to the emission in the visible range.
我们使用时间分辨光谱技术研究了双（2-苯基吡啶基）（2,2'-联吡啶）铱（III），[Ir（ppy）（2）bpy]（+）的弛豫动力学。在可见发射光谱中，该分子表现出三重磷光：显示蓝色、绿色和橙色带。从溶剂极性对光谱位移、衰减寿命的依赖性以及使用时间相关密度泛函理论的计算结果，我们将这三种发射态分配给三重配体间电荷转移（（3）LLCT）、金属-配体 ppy 电荷转移（（3）MLCT（ppy））和金属-配体 bpy 电荷转移（（3）MLCT（bpy））态。蓝色态在 355nm 波长激发后立即形成；能量较高的一个以 0.79-2.56ns 的时间系数衰减，被分配为三重 MLCT，而能量较低的一个在 1.5-2.8μs 内衰减，被分配为（3）LLCT（A），A 对称。（3）LLCT（A）的这个衰减时间系数随着溶剂介电常数的增加而减小，表明该态具有一些 MLCT 特征的混合。绿色态（3）MLCT（ppy）在 0.13-4.8ns 内衰减到附近的中间态（3）MLCT（ppy）或（3）MLCT（bpy）。橙色态（3）MLCT（bpy）与中间态耦合，具有约 0.36-0.84ns 的上升时间，并在 425-617ns 内衰减。尽管许多三重态存在于小能量范围内，但它们耦合较弱，表现出三重发射。所有（3）LLCT 和（3）MCLT 态都直接和/或间接地与单重（1）LLCT 态系耦合，并对可见范围内的发射作出贡献。
