Sajoto Tissa, Djurovich Peter I, Tamayo Arnold B, Oxgaard Jonas, Goddard William A, Thompson Mark E
Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA.
J Am Chem Soc. 2009 Jul 22;131(28):9813-22. doi: 10.1021/ja903317w.
The photophysical properties for a series of facial (fac) cyclometalated Ir(III) complexes (fac-Ir(C--N)(3) (C--N = 2-phenylpyridyl (ppy), 2-(4,6-difluorophenyl)pyridyl (F2ppy), 1-phenylpyrazolyl (ppz), 1-(2,4-difluorophenyl)pyrazolyl) (F2ppz), and 1-(2-(9,9'-dimethylfluorenyl))pyrazolyl (flz)), fac-Ir(C--N)(2)(C--N') (C--N = ppz or F2ppz and C--N' = ppy or F2ppy), and fac-Ir(C--C')(3) (C--C' = 1-phenyl-3-methylbenzimidazolyl (pmb)) have been studied in dilute 2-methyltetrahydrofuran (2-MeTHF) solution in a temperature range of 77-378 K. Photoluminescent quantum yields (Phi) for the 10 compounds at room temperature vary between near zero and unity, whereas all emit with high efficiency at low temperature (77 K). The quantum yield for fac-Ir(ppy)(3) (Phi = 0.97) is temperature-independent. For the other complexes, the temperature-dependent data indicates that the luminescent efficiency is primarily determined by thermal deactivation to a nonradiative state. Activation energies and rate constants for both radiative and nonradiative processes were obtained using a Boltzmann analysis of the temperature-dependent luminescent decay data. Activation energies to the nonradiative state are found to range between 1600 and 4800 cm(-1). The pre-exponential factors for deactivation are large for complexes with C--N ligands (10(11)-10(13) s(-1)) and significantly smaller for fac-Ir(pmb)(3) (10(9) s(-1)). The kinetic parameters for decay and results from density functional theory (DFT) calculations of the triplet state are consistent with a nonradiative process involving Ir-N (Ir-C for fac-Ir(pmb)(3)) bond rupture leading to a five-coordinate species that has triplet metal-centered ((3)MC) character. Linear correlations are observed between the activation energy and the energy difference calculated for the emissive and (3)MC states. The energy level for the (3)MC state is estimated to lie between 21,700 and 24,000 cm(-1) for the fac-Ir(C--N)(3) complexes and at 28,000 cm(-1) for fac-Ir(pmb)(3).
在77 - 378 K的温度范围内，研究了一系列面式（fac）环金属化铱（III）配合物（fac-Ir（C-N）3（C-N = 2-苯基吡啶基（ppy）、2-（4,6-二氟苯基）吡啶基（F2ppy）、1-苯基吡唑基（ppz）、1-（2,4-二氟苯基）吡唑基（F2ppz）和1-（2-（9,9'-二甲基芴基））吡唑基（flz））、fac-Ir（C-N）2（C-N'）（C-N = ppz或F2ppz且C-N' = ppy或F2ppy）以及fac-Ir（C-C'）3（C-C' = 1-苯基-3-甲基苯并咪唑基（pmb））在稀2-甲基四氢呋喃（2-MeTHF）溶液中的光物理性质。这10种化合物在室温下的光致发光量子产率（Φ）在接近零到1之间变化，而在低温（77 K）下均高效发光。fac-Ir（ppy）3的量子产率（Φ = 0.97）与温度无关。对于其他配合物，温度相关数据表明发光效率主要由热失活至非辐射态决定。使用对温度相关发光衰减数据的玻尔兹曼分析获得了辐射和非辐射过程的活化能和速率常数。发现至非辐射态的活化能在1600至4800 cm-1之间。具有C-N配体的配合物失活的预指数因子较大（1011 - 1013 s-1），而fac-Ir（pmb）3的预指数因子明显较小（109 s-1）。衰减的动力学参数以及三线态的密度泛函理论（DFT）计算结果与涉及Ir-N（fac-Ir（pmb）3为Ir-C）键断裂导致具有三线态金属中心（（3）MC）特征的五配位物种的非辐射过程一致。在活化能与发射态和（3）MC态计算的能量差之间观察到线性相关性。对于fac-Ir（C-N）3配合物，（3）MC态的能级估计在21,700至24,000 cm-1之间，对于fac-Ir（pmb）3为28,000 cm-1。
