Intersystem-crossing and phosphorescence rates in fac-IrIII(ppy)3: A theoretical study involving multi-reference configuration interaction wavefunctions
Intersystem-crossing and phosphorescence rates in fac-IrIII(ppy)3: A theoretical study involving multi-reference configuration interaction wavefunctions
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DOI：
10.1063/1.4913513
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发表时间：
2015-03-07
影响因子：
4.4
通讯作者：
Marian, Christel M.
中科院分区：
文献类型：
--
作者：
Kleinschmidt, Martin;van Wuellen, Christoph;Marian, Christel M.
本文采用结合密度泛函理论和包括自旋轨道耦合（SOC）效应在内的多参考组态相互作用方法研究了绿色磷光发射体faci -tris-（2-苯基吡啶）铱(faci - ir （ppy)(3)）的光物理性质。对量子化学方法的关键评价表明，SOC的微扰处理是计算这种重过渡金属配合物的紫外/可见光谱的首选方法，而多参考自旋轨道组态相互作用更适合计算磷光率。发现自旋轨道相互作用算符的特殊选择是次要的。系统间交叉（ISC）速率由包含Dushinsky旋转的跃迁时间相关函数的傅里叶变换确定。在电子基态，面- ir (ppy)(3)是C-3对称的。计算得到的紫外/可见光谱与实验结果吻合良好。SOC的影响在吸收光谱可见区域的金属-配体电荷转移（MLCT）波段尤为明显，该波段不仅将其光谱起始波长延长到更长的波长，而且还经历了最大的蓝移。伪jahn - teller相互作用导致最低MLCT态的不对称坐标位移。大量的电子SOC和小的能隙使得ISC在face - ir （ppy）中成为一个超快过程(3)。对于s -1 T-1非辐射跃迁，我们计算了k(ISC) = 6.9 x 10(12) s（-1）的速率常数，该速率常数超过了辐射衰变到电子基态的速率常数6个数量级以上，与亚皮秒ISC过程的实验观察和接近1的三重态量子产率一致。由于T-1态的几何畸变，T-1 -> S-0跃迁密度定位在一个苯基吡啶基基团上。在我们的最佳量子化学模型中，我们获得了二氯甲烷（DCM）溶液中T-1、T-I、T-1、T-II和T-1、T-III精细结构水平的磷光衰减时间分别为264 μ s、13 μ s和0.9 μ s。除了再现单个磷光发射概率的正确数量级外，我们的理论研究还深入了解了潜在的机制。从允许自旋跃迁的强度借用来看，T-1，T-I子态的低发射概率是由于几个单重态对总跃迁偶极矩的贡献相互抵消造成的。在更快的T-1，T-III -> S-0发射的情况下，它们的贡献不会抵消，而是加在一起，而T-1，T-II -> S-0发射主要是由单个自旋允许过程的强度借用，即S-2 -> S-0跃迁。(c) 2015 AIP出版有限责任公司
We have employed combined density functional theory and multi-reference configuration interaction methods including spin-orbit coupling (SOC) effects to investigate the photophysics of the green phosphorescent emitter fac-tris-(2-phenylpyridine)iridium (fac-Ir(ppy)(3)). A critical evaluation of our quantum chemical approaches shows that a perturbational treatment of SOC is the method of choice for computing the UV/Vis spectrum of this heavy transition metal complex while multi-reference spin-orbit configuration interaction is preferable for calculating the phosphorescence rates. The particular choice of the spin-orbit interaction operator is found to be of minor importance. Intersystem crossing (ISC) rates have been determined by Fourier transformation of the time correlation function of the transition including Dushinsky rotations. In the electronic ground state, fac-Ir(ppy)(3) is C-3 symmetric. The calculated UV/Vis spectrum is in excellent agreement with experiment. The effect of SOC is particularly pronounced for the metal-to-ligand charge transfer (MLCT) band in the visible region of the absorption spectrum which does not only extend its spectral onset towards longer wavelengths but also experiences a blue shift of its maximum. Pseudo-Jahn-Teller interaction leads to asymmetric coordinate displacements in the lowest MLCT states. Substantial electronic SOC and a small energy gap make ISC an ultrafast process in fac-Ir(ppy)(3). For the S-1 T-1 non-radiative transition, we compute a rate constant of k(ISC) = 6.9 x 10(12) s(-1) which exceeds the rate constant of radiative decay to the electronic ground state by more than six orders of magnitude, in agreement with the experimental observation of a subpicosecond ISC process and a triplet quantum yield close to unity. As a consequence of the geometric distortion in the T-1 state, the T-1 -> S-0 transition densities are localized on one of the phenylpyridyl moieties. In our best quantum chemical model, we obtain phosphorescence decay times of 264 mu s, 13 mu s, and 0.9 mu s, respectively, for the T-1,T-I, T-1,T-II, and T-1,T-III fine-structure levels in dichloromethane (DCM) solution. In addition to reproducing the correct orders of magnitude for the individual phosphorescence emission probabilities, our theoretical study gives insight into the underlying mechanisms. In terms of intensity borrowing from spin-allowed transitions, the low emission probability of the T-1,T-I substate is caused by the mutual cancellation of contributions from several singlet states to the total transition dipole moment. Their contributions do not cancel but add up in case of the much faster T-1,T-III -> S-0 emission while the T-1,T-II -> S-0 emission is dominated by intensity borrowing from a single spin-allowed process, i.e., the S-2 -> S-0 transition. (c) 2015 AIP Publishing LLC.