Laboratory of Photonics and Interfaces, Institute of Chemical Sciences and Engineering, School of Basic Sciences, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.
Inorg Chem. 2012 Jan 16;51(2):799-811. doi: 10.1021/ic2011474. Epub 2011 Dec 22.
A series of homologous bis-cyclometalated iridium(III) complexes Ir(2,4-di-X-phenyl-pyridine)(2)(picolinate) (X = H, F, Cl, Br) HIrPic, FIrPic, ClIrPic, and BrIrPic has been synthesized and characterized by NMR, X-ray crystallography, UV-vis absorption and emission spectroscopy, and electrochemical methods. The addition of halogen substituents results in the emission being localized on the main cyclometalated ligand. In addition, halogen substitution induces a blue shift of the emission maxima, especially in the case of the fluoro-based analogue but less pronounced for chlorine and bromine substituents. Supported by ground and excited state theoretical calculations, we rationalized this effect in a simple manner by taking into account the σp and σm Hammett constants on both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels. Furthermore, in comparison with FIrPic and ClIrPic, the impact of the large bromine atom remarkably decreases the photoluminescence quantum yield of BrIrPic and switches the corresponding lifetime from mono to biexponential decay. We performed theoretical calculations based on linear-response time-dependent density functional theory (LR-TDDFT) including spin-orbit coupling (SOC), and unrestricted DFT (U-DFT) to obtain information about the absorption and emission processes and to gain insight into the reasons behind this remarkable change in photophysical properties along the homologous series of complexes. According to theoretical geometries for the lowest triplet state, the large halogen substituents contribute to sizable distortions of specific phenylpyridine ligands for ClIrPic and BrIrPic, which are likely to play a role in the emissive and nonradiative properties when coupled with the heavy-atom effect.
一系列同系的双环金属铱（III）配合物 Ir(2,4-二-X-苯基吡啶)(2)(吡啶甲酸)（X = H、F、Cl、Br），即 HIrPic、FIrPic、ClIrPic 和 BrIrPic，已通过 NMR、X 射线晶体学、紫外可见吸收和发射光谱以及电化学方法进行了合成和表征。卤素取代基的加入导致发射局域在主要的环金属化配体上。此外，卤素取代基诱导发射峰的蓝移，特别是在基于氟的类似物的情况下，但氯和溴取代基的蓝移程度较小。基于地面和激发态理论计算，我们通过考虑最高占据分子轨道（HOMO）和最低未占据分子轨道（LUMO）能级上的σp 和 σm 哈米特常数，以简单的方式对这种效应进行了合理化。此外，与 FIrPic 和 ClIrPic 相比，大溴原子的影响显著降低了 BrIrPic 的光致发光量子产率，并将相应的寿命从单指数衰减转变为双指数衰减。我们进行了基于线性响应含时密度泛函理论（LR-TDDFT）的理论计算，包括自旋轨道耦合（SOC）和非限制密度泛函（U-DFT），以获取有关吸收和发射过程的信息，并深入了解该同系物系列配合物中光物理性质显著变化的原因。根据最低三重态的理论几何形状，大的卤素取代基有助于 ClIrPic 和 BrIrPic 中特定的苯基吡啶配体的明显扭曲，当与重原子效应结合时，这可能在发光和非辐射性质中发挥作用。
