Design,Synthesis And Characterization Of OLED Dopants Based On Platinum(Ⅱ) And Iridium(Ⅲ) Complexes

Organic Electroluminescent diodes(OLEDs) compared with the traditional lighting and display technologies domenstrate many advantages such as high brightness, low power consumption. Particularly OLED displays feature high contrast, wide viewing angle, full-color and wide operating temperature range. The past decade has witnessed the great development in OLEDs. The chromaticity, stability and efficiency of red color and green OLEDs can meet the criteria for the practical application. However, the blue emitters show poor device performance in terms of chromaticity, efficiency and lifetime. When applied as OLED dopants, metal complexes can harvest both singlet and triplet excitons to achieve high efficiency. Thus, our work will focus on the design and synthesis of blue emitters based on the platinum and iridium complexes.The first part of our work is to design and synthesize a series of unsymmetric tetradentate Pt complexes as dopants for OLEDs. A series of highly phosphorescent Pt(II) complexes(Pt1-Pt3) based on rigid unsymmetric tetradentate ligands(L1-L3) were designed and synthesized. L1-L3 ligands are an analogue to N,N-di(2-phenylpyrid-6-yl)aniline(L) except that one coordination phenyl group in L has been replaced by other motifs with different electron donating/accepting capabilities. The effect associated with the modulation of a single coordination group within each ligand on the photophysical and electroluminescent properties of Pt1-Pt3 was investigated systematically. Among Pt1-Pt3, Pt1 has the highest HOMO due to the presence of a strong electron-donating group(3-methylindole), and exhibits the narrowest bandgap; Pt2 has the lowest HOMO due to the lack of strong donor group within the structure, and shows the widest bandgap. Organic light-emitting diodes(OLEDs) based on these three complexes showed yellowish green to greenish yellow electroluminescence with high efficiency. Notably, the device based on Pt1 at the doping level of 10 wt% achieved a maximum efficiency of 53.0 cd A-1, 35.9 lm W-1 and 16.3% with CIE coordinates of(0.44, 0.53).The second part of our work is to design and synthesize metal(Ir and Pt) complexes based on pyrazolo[1,5-f]phenanthridine motif with the help of DFT calculation. The rigidity of the ligand may contribute to the thermal stability of metal complexes. As predicted by DFT calculation, the as-synthesized iridium(III) complexes are blue emitters. The synthesis and characterization of Pt(II) complexes are still under investigation.