Versatile Pt(II) Pyrazolate Complexes: Emission Tuning via Interplay of Chelate Designs and Stacking Assemblies

• Published in: ACS applied materials & interfaces Vol. 12; no. 14; pp. 16679 - 16690
• Main Authors: Ko, Chang-Lun, Hung, Wen-Yi, Chen, Po-Ting, Wang, Tsai-Hui, Hsu, Hsiu-Fu, Liao, Jia-Ling, Ly, Kiet Tuong, Wang, Sheng Fu, Yu, Chang-Hung, Liu, Shih-Hung, Lee, Gene-Hsiang, Tai, Wun-Shan, Chou, Pi-Tai, Chi, Yun
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 08.04.2020
• Subjects: dimethyl sulfoxide; films (materials); light emitting diodes; platinum; pyrazoles; tetrahydrofuran; X-ray diffraction; pyrazole; pyridine; platinum; aggregation; light-emitting diodes; imidazole
• ISSN: 1944-8244; 1944-8252; 1944-8252
• DOI: 10.1021/acsami.9b23388

Three homoleptic Pt­(II) metal complexes [Pt­(imPz)2] (1), [Pt­(imiz)2] (2), and [Pt­(imMz)2] (3) were synthesized from the treatment of Pt­(DMSO)2Cl2 and functional imidazolyl pyrazole in refluxing tetrahydrofuran (THF). Alternatively, the heteroleptic Pt­(II) complexes [Pt­(imPz)­(fppz)] (4), [Pt­(imiz)­(fppz)] (5), and [Pt­(imMz)­(fppz)] (6) were obtained from the treatment of a common intermediate [Pt­(fppzH)­Cl2] with a corresponding imidazolyl chelate. Pt­(II) complexes 1, 2, and 5 were studied by single-crystal X-ray diffraction to reveal the corresponding packing arrangement in their crystal lattices, among which both homoleptic complexes 1 and 2 formed monomeric species, while heteroleptic 5 aligned as a dimer with a nonbonding Pt···Pt contact of 3.574 Å. Subsequent photophysical examinations showed that the homoleptic 1–3 and heteroleptic 4–6 exhibited the structured sky-blue ππ* emission and structureless light-green-emitting metal–metal-to-ligand charge transfer (MMLCT) emission in the solid state, respectively. A shortened Pt···Pt interaction of approximately 0.34–0.35 nm was confirmed in thin films of all heteroleptic Pt­(II) complexes 4–6 by grazing-incidence X-ray diffraction (GIXD) analyses. Finally, Pt­(II) complex 6 was employed as a dopant in the fabrication of organic light-emitting diode (OLED) devices with varied doping ratios, among which OLEDs with only 1 wt % 6 in the SimCP host exhibited a maximum external quantum efficiency (EQE) of 5.8% and CIE x,y values of 0.20, 0.31. In contrast, OLEDs using a nondoped architecture (i.e., 100% of 6 in the emitting layer (EML)) achieved a maximum EQE of 26.8%, current efficiency (CE) of 91.7 cd A–1, and power efficiency (PE) of 80.1 lm·W–1 and CIE x,y values of 0.41, 0.55, manifesting their versatility in various degrees of stacking assemblies and hence facile color-tuning capability on OLEDs.