Centre for Organic Photonics & Electronics, The University of Queensland, Brisbane, Queensland 4072, Australia.
Inorg Chem. 2012 Mar 5;51(5):2821-31. doi: 10.1021/ic201899z. Epub 2012 Feb 16.
We use a combination of low temperature, high field magnetic circular dichroism, absorption, and emission spectroscopy with relativistic time-dependent density functional calculations to reveal a subtle interplay between the effects of chemical substitution and spin-orbit coupling (SOC) in a family of iridium(III) complexes. Fluorination at the ortho and para positions of the phenyl group of fac-tris(1-methyl-5-phenyl-3-n-propyl-[1,2,4]triazolyl)iridium(III) cause changes that are independent of whether the other position is fluorinated or protonated. This is demonstrated by a simple linear relationship found for a range of measured and calculated properties of these complexes. Further, we show that the phosphorescent radiative rate, k(r), is determined by the degree to which SOC is able to hybridize T(1) to S(3) and that k(r) is proportional to the inverse fourth power of the energy gap between these excitations. We show that fluorination in the para position leads to a much larger increase of the energy gap than fluorination at the ortho position. Theory is used to trace this back to the fact that fluorination at the para position increases the difference in electron density between the phenyl and triazolyl groups, which distorts the complex further from octahedral symmetry, and increases the energy separation between the highest occupied molecular orbital (HOMO) and the HOMO-1. This provides a new design criterion for phosphorescent iridium(III) complexes for organic optoelectronic applications. In contrast, the nonradiative rate is greatly enhanced by fluorination at the ortho position. This may be connected to a significant redistribution of spectral weight. We also show that the lowest energy excitation, 1A, has almost no oscillator strength; therefore, the second lowest excitation, 2E, is the dominant emissive state at room temperature. Nevertheless the mirror image rule between absorption and emission is obeyed, as 2E is responsible for both absorption and emission at all but very low (<10 K) temperatures.
我们结合低温、强磁场圆二色性、吸收和发射光谱以及相对论含时密度泛函计算，揭示了一系列铱(III)配合物中化学取代和自旋轨道耦合(SOC)效应之间的微妙相互作用。在 fac-tris(1-甲基-5-苯基-3-正丙基-[1,2,4]三唑基)铱(III)的苯基的邻位和对位进行氟化会导致一些变化，而这些变化与另一位点是否被氟化或质子化无关。这可以通过对这些配合物的一系列测量和计算性质的简单线性关系得到证明。此外，我们表明磷光辐射速率 k(r)取决于 SOC 使 T(1)与 S(3)杂化的程度，并且 k(r)与这些激发之间的能量间隙的倒数四次方成比例。我们表明，在对位进行氟化比在邻位进行氟化会导致能量间隙增加得更大。理论被用来追溯到这样一个事实，即在对位进行氟化会增加苯基和三唑基之间的电子密度差异，从而使配合物进一步偏离八面体对称性，并增加最高占据分子轨道(HOMO)和 HOMO-1 之间的能量分离。这为有机光电应用中的磷光铱(III)配合物提供了新的设计准则。相比之下，在邻位进行氟化会极大地增强非辐射速率。这可能与光谱权重的显著重新分配有关。我们还表明，最低能量激发态 1A 几乎没有振子强度；因此，在室温下，第二低激发态 2E 是主要的发射态。尽管吸收和发射之间的镜像规则得到遵守，因为 2E 在几乎所有温度（<10 K 除外）下都负责吸收和发射。
