Pal Amlan K, Cordes David B, Slawin Alexandra M Z, Momblona Cristina, Ortı Enrique, Samuel Ifor D W, Bolink Henk J, Zysman-Colman Eli
Organic Semiconductor Centre, EaStCHEM School of Chemistry, University of St Andrews , St Andrews, Fife KY16 9ST, United Kingdom.
EaStCHEM School of Chemistry, University of St Andrews , St Andrews, Fife KY16 9ST, United Kingdom.
Inorg Chem. 2016 Oct 17;55(20):10361-10376. doi: 10.1021/acs.inorgchem.6b01602. Epub 2016 Sep 28.
The structure-property relationship study of a series of cationic Ir(III) complexes in the form of [Ir(C^N)(dtBubpy)]PF [where dtBubpy = 4,4'-di-tert-butyl-2,2'-bipyridine and C^N = cyclometallating ligand bearing an electron-withdrawing group (EWG) at C of the phenyl substituent, i.e., -CF (1), -OCF (2), -SCF (3), -SOCF (4)] has been investigated. The physical and optoelectronic properties of the four complexes were comprehensively characterized, including by X-ray diffraction analysis. All the complexes exhibit quasireversible dtBubpy-based reductions from -1.29 to -1.34 V (vs SCE). The oxidation processes are likewise quasireversible (metal + C^N ligand) and are between 1.54 and 1.72 V (vs SCE). The relative oxidation potentials follow a general trend associated with the Hammett parameter (σ) of the EWGs. Surprisingly, complex 4 bearing the strongest EWG does not adhere to the expected Hammett behavior and was found to exhibit red-shifted absorption and emission maxima. Nevertheless, the concept of introducing EWGs was found to be generally useful in blue-shifting the emission maxima of the complexes (λ = 484-545 nm) compared to that of the prototype complex [Ir(ppy)(dtBubpy)]PF (where ppy = 2-phenylpyridinato) (λ = 591 nm). The complexes were found to be bright emitters in solution at room temperature (Φ = 45-66%) with microsecond excited-state lifetimes (τ = 1.14-4.28 μs). The photophysical properties along with density functional theory (DFT) calculations suggest that the emission of these complexes originates from mixed contributions from ligand-centered (LC) transitions and mixed metal-to-ligand and ligand-to-ligand charge transfer (LLCT/MLCT) transitions, depending on the EWG. In complexes 1, 3, and 4 the LC character is prominent over the mixed CT character, while in complex 2, the mixed CT character is much more pronounced, as demonstrated by DFT calculations and the observed positive solvatochromism effect. Due to the quasireversible nature of the oxidation and reduction waves, fabrication of light-emitting electrochemical cells (LEECs) using these complexes as emitters was possible with the LEECs showing moderate efficiencies.
对一系列阳离子铱（III）配合物[Ir(C^N)(dtBubpy)]PF（其中dtBubpy = 4,4'-二叔丁基-2,2'-联吡啶，C^N = 在苯基取代基的C原子上带有吸电子基团（EWG）的环金属化配体，即-CF₃(1)、-OCF₃(2)、-SCF₃(3)、-SOCF₃(4)）的结构-性质关系进行了研究。对这四种配合物的物理和光电性质进行了全面表征，包括通过X射线衍射分析。所有配合物均表现出基于dtBubpy的准可逆还原，还原电位为-1.29至-1.34 V（相对于饱和甘汞电极）。氧化过程同样是准可逆的（金属 + C^N配体），氧化电位在1.54至1.72 V（相对于饱和甘汞电极）之间。相对氧化电位遵循与EWG的哈米特参数（σ）相关的一般趋势。令人惊讶的是，带有最强EWG的配合物4并不遵循预期的哈米特行为，发现其吸收和发射最大值出现红移。然而，发现引入EWG的概念通常有助于使配合物的发射最大值发生蓝移（λ = 484 - 545 nm），相比原型配合物[Ir(ppy)(dtBubpy)]PF（其中ppy = 2-苯基吡啶基）（λ = 591 nm）。发现这些配合物在室温下的溶液中是明亮的发光体（Φ = 45 - 66%），激发态寿命为微秒级（τ = 1.14 - 4.28 μs）。光物理性质以及密度泛函理论（DFT）计算表明，这些配合物的发射源于配体中心（LC）跃迁以及混合的金属到配体和配体到配体电荷转移（LLCT/MLCT）跃迁的混合贡献，这取决于EWG。在配合物1、3和4中，LC特征比混合CT特征更突出，而在配合物2中，混合CT特征更为明显，这通过DFT计算和观察到的正溶剂化显色效应得到证明。由于氧化和还原波的准可逆性质，使用这些配合物作为发光体制造发光电化学电池（LEEC）是可能的，LEEC显示出中等效率。
