State Key Laboratory Breeding Base of Green Chemistry-Synthesis Technology, College of Chemical Engineering , Zhejiang University of Technology , Hangzhou , Zhejiang 310014 , P. R. China.
Inorg Chem. 2019 Nov 4;58(21):14349-14360. doi: 10.1021/acs.inorgchem.9b01617. Epub 2019 Sep 9.
The synthesis and photophysical characterization of a series of tetradentate cyclometalated M(Ph-O-CzPy-R) complexes and their analogues are reported, where M is palladium or platinum and a tetradentate cyclometalating ligand contains Ph (3-phenyl-[1,2,4]triazolo[4,3-]pyridine) and CzPy (carbazolylpyridine) moieties linked with an oxygen atom. Variations of the σ-electron-donating group R on the ligand significantly affect the photophysical properties of the complexes. By using the strong electron-withdrawing portion as an acceptor and the carbazole portion as a donor, a series of Pd(II)-based metal-assisted delayed fluorescence (MADF) materials was developed. Electrochemical analysis demonstrates the irreversible reduction process occurs on the ring and the irreversible oxidation process mainly occurs on the metal-phenyl moiety. This is in agreement with the HOMO and LUMO distributions by the DFT calculations, which also shows that the Pt(II) complex has more metal orbital character than those of the Pd(II) complexes. Most of the Pd(II) complexes reported here are highly emissive at 77 K in 2-MeTHF with luminescent lifetimes in the millisecond range (τ = 1.96-2.36 ms) and λ = 488-499 nm; however, the luminescent lifetimes are shortened to the microsecond range (τ = 26.7-152.9 μs in solution and 57.0-109.9 μs in thin film respectively) at room temperature. The quantum efficiency of the Pd(II) complexes can be increased by more than 8-fold through structure modification with σ-donating groups on the ligand. Especially, the Pd(-3) has a small Δ of 0.228 eV and exhibits strong typical MADF in PMMA film. The Pt(II) complex Pt(-2) exhibits high thermal stability (Δ = 440 °C) and high quantum efficiency (Φ = 50.1%) in dichloromethane solution with τ of 15.8 μs. The Pt(-2) based bright green OLED achieved a peak EQE of 8.7% and a maximum brightness of 28280 cd/m using an unoptimized device structure.
报告了一系列四齿螯合金属配合物 M(Ph-O-CzPy-R)及其类似物的合成和光物理特性，其中 M 是钯或铂，四齿螯合配体含有 Ph（3-苯基-[1,2,4]三唑并[4,3-]吡啶）和 CzPy（咔唑基吡啶）部分，通过氧原子连接。配体上 σ-给电子基团 R 的变化显著影响配合物的光物理性质。通过使用强吸电子部分作为受体和咔唑部分作为供体，开发了一系列基于 Pd(II)的金属辅助延迟荧光 (MADF) 材料。电化学分析表明，在环上发生不可逆还原过程，在金属-苯基部分主要发生不可逆氧化过程。这与 DFT 计算的 HOMO 和 LUMO 分布一致，这也表明 Pt(II)配合物比 Pd(II)配合物具有更多的金属轨道特征。这里报道的大多数 Pd(II)配合物在 2-MeTHF 中于 77 K 下高度发光，具有毫秒级的荧光寿命（τ = 1.96-2.36 ms）和 λ = 488-499nm；然而，在室温下，荧光寿命缩短至微秒范围（τ = 26.7-152.9 μs 在溶液中和 57.0-109.9 μs 在薄膜中）。通过在配体上引入 σ-给电子基团进行结构修饰，可以使 Pd(II)配合物的量子效率提高 8 倍以上。特别是，Pd(-3)具有小的Δ值为 0.228 eV，并在 PMMA 薄膜中表现出强典型的 MADF。Pt(II)配合物 Pt(-2)在二氯甲烷溶液中具有高的热稳定性（Δ = 440°C）和高的量子效率（Φ = 50.1%），τ为 15.8 μs。基于 Pt(-2)的明亮绿色 OLED 使用未经优化的器件结构实现了 8.7%的峰值 EQE 和 28280 cd/m 的最大亮度。
