Synthesis And Properties Of Dinuclear Cyclometalated Iridium And Platinum Complexes

The development and status of organic electrophosphorescent materials and white organic light-emitting devices (WOLEDs) were reviewed in this dissertation. In order to solve the problems, such as scarce single white-emitting organic materials, low luminescent efficiency and bad chroma stability for the devices, we designed and synthesized two classes of dinuclear platinum-iridium complexes, as well as study their thermal, photophysical, electrochemical and electroluminescent properties. The key results are listed as followed.1. Two classes of dinuclear platinum-iridium complexes were designed by two connected ways of the bi(picolinic acid) anion ligand (pic-pic) and the anion-C^N cyclometalated ligand (pic-ppy). These platinum-iridium dinuclear complexes were synthesized by a series of reactions, such as Vilsmeirer-Haack reaction, Miyaura- Suzuki coupling reaction and Williamson ether-forming reaction.2. The decomposed temperatures were about 261 292℃for these dinuclear platinum -iridium complexes. Compared to iridium(Ⅲ) di(4,6-difluophenyl pyridinate-C²,N) (picolinate) [FIr(pic)], these dinuclear platinum-iridium complexes presented better thermal stability.3. These dinuclear platinum-iridium complexes exhibited as an intense absorption band about 255 nm from the ligand-to-ligand charge transfer (LLCT) transition and a weak absorption band about 374 nm from the metal-to-ligand charge transfer (MLCT) transition. Introduction of carrier-transporting group into the complexes is available to enhance the LLCT absorption for these dinuclear platinum-iridium complexes. Compared to platinum (Ⅱ) (4,6-difluophenyl pyridinate-C²,N) (picolinate) [FPt(pic)], None of these platinum-iridium complexes displayed the absorption band about 328 nm from metal-to-metal-to-ligand charge transfer (MMLCT) transition.4. All these complexes gave a nearly identical photoluminescence (PL) spectrum in dichloromethane (DCM). The maximum emission peak at 469 481 nm with a shoulder at 495 505 nm was observed. Compared to the pic-ppy-based dinuclear platinum-iridium complexes, the pic-pic-based ones presented 7 nm blue-shifted PL spectra. It is noted that two classes of dinuclear platinum-iridium complexes showed different PL spectra in their neat films. None of the pic-pic-based ones presented excimer emission. However, all of the pic-ppy-based ones displayed strong excimer emission about 609 658 nm. This indicates that the formation of molecular aggrega- tion state can be effectively tuned by different connected ways.5. The highest occupied molecular orbital energy levels (E_HOMO) were in the range of -5.51 -6.06 eV,and the lowest unoccupied molecular orbital energy levels (E_LUMO) were around -3.08 -3.20 eV for these dinuclear platinum-iridium complexes. Compared to FPt(pic), these dinuclear platinum-iridium complexes presented higher E_HOMO and E_LUMO.6. The single-layer polymer light-emitting devices (PLEDs) were fabricated by using these dinuclear platinum-iridium complexes as dopants and poly(vinyl-carbazole) (PVK) as host matrix. While the dinuclear platinum-iridium complex of FIr(pic)- C₆OXDC₆-FPt(pic) was used as a single doapnt, the device exhibited near-white emission with a CIE coordinate (0.33, 0.38) at a 1% doping concentration and a applied voltages of 14V. The dinuclear platinum-iridium complex of FIr(pic)- C₆-FPt(pic) at 8% doping concentration, the device presented the maximal luminance of 935 cd m^-2 and current efficiency of 1.24 cd A^-1, respectively.This investigation has laid a well foundation for further study on the dinuclear and multi-nuclear complexes used as white-emitting organic materials. It may promote the development of the white-emiting PLEDs with high stability and efficiency.