Design,Synthesis And Photoelectric Properties Of Several Iridium(Ⅲ)Complexes

Organic Light-Emitting Diodes(OLEDs)have attracted considerable attention on account of their remarkable properties,such as low-cost,wide viewing angle,bright color and flexible displays.Phosphorescence iridium(Ⅲ)complexes are the most promising candidates for efficient OLEDs,owing to their good stability,short excited state lifetime,flexible color tunability and high quantum efficiency.In this thesis,a series of new iridium(Ⅲ)complexes were designed and synthesized based on different types of cyclometalated ligands by introducing different substituent groups or changing the spatial structures.The photophysical properties and OLED performances of the complexes were investigated and discussed in detail.1.Based on the precursor ligand 1-phenylpyrazole(2a),we designed ppz derivatives(2a-2g)as the main ligands by introducing benzene group to increase theπ system and fluorine group to enhance the photoluminescence quantum yields.According to the different positions of benzene group on the main ligands,they can be divided into two series:ligands 2b-2d(looking like the number“1”)and ligands 2e-2g(looking like the number“7”).And then we synthesized seven Ir(Ⅲ)complexes Ir1-Ir7 with ppz derivatives 2a-2g as the main ligands and tetraphenylimidodiphosphinate(tpip)as the ancillary ligand.Their emission colors can be adjusted from blue to yellow in CH2Cl2 solution,which may be attributed to the fact that different spatial structures lead to different photophysical properties(emission peak,quantum efficiency,lifetime,etc.).The monochrome phosphorescent devices Ⅰ-D1,Ⅰ-D3,Ⅰ-D4,Ⅰ-D6 and Ⅰ-D7 using Ir(Ⅲ)complexes Ir1,Ir3,Ir4,Ir6 and Ir7 as the emitters emit blue,yellow and bluish-green light,respectively.Compared with the device Ⅰ-D1,the devices Ⅰ-D3,Ⅰ-D4,Ⅰ-D6,Ⅰ-D7 displayed much better performances.The results indicate that the "7" character of the main ligands by introducing the bulky-CF3 series can affect the packing of molecular and further improve the performance,which provides a new idea for adjusting the luminescent color of the iridium(Ⅲ)complex and improving the luminescent properties of these material.2.Four phosphorescent bis-cyclometalated 2-(2-thienyl)pyridine-based Ir(Ⅲ)complexes with tpip as the ancillary ligand,(thp)2Ir(tpip),(cf3thp)2Ir(tpip),(cf3btp)2Ir(tpip)and(3-cf3btp)2Ir(tpip),were synthesized by introducing-CF3 group,increasing π-conjugation system and/or changing phenyl connection position of the cyclometalated ligands.The emission colors of these Ir(Ⅲ)complexes can be adjusted from yellow to deep red in CH2C12 solution at 298 K.The phosphorescent OLEDs Ⅱ-D1～Ⅱ-D3 comprising(thp)2Ir(tpip),(cf3thp)2Ir(tpip)and(cf3btp)2Ir(tpip)as yellow,orange,and deep red dopants realize state-of-art device performances with EQEmax of 11.3%,17.9%and 10.8%and low efficiency roll-off,which still remain high EQE of 10.0%,15.4%and 7.3%at a luminance of 1000 cd·m-2,respectively.These results suggest that the rational design of Ir(Ⅲ)complexes based on 2-(2-thienyl)pyridine derivatives is an effective method for the development of high performance OLEDs.3.We synthesized four Ir(Ⅲ)complexes with 2-phenylbenzothiazole(bt)derivatives as the cyclometalated ligands and tpip as the ancillary ligand((bt)2Ir(tpip),(fbt)2Ir(tpip),(cf3bt)2Ir(tpip)and(dfbt)21r(tpip)),wherein the cyclometalated C^N ligands were obtained by a simple and efficient method using benzaldehyde and substituted aminothiophenol.All complexes emit yellow lights peak at 564-574 nm with quantum efficiencies(Φem)of 27.1-48.4%and excited state lifetimes of 2.40-2.81 μs in degassed CH2Cl2 solution at room temperature,respectively.Correspondingly,the organic light-emitting diodes(OLEDs)using these complexes as emitters achieve yellow electrophosphorescence with good device characteristics.Due to its highest photoluminescence quantum yield(48.4%),the device Ⅲ-D4 based on(dfbt)2Ir(tpip)displays the best device performances with a maximum current efficiency(ηc,max)up to 69.8 cd A-1 and a maximum external quantum efficiency(EQEmax)up to 24.3%.Furthermore,all devices showed low efficiency roll-off ratios.The EQE still could be retained at 17.7%,16.4%,18.3%and 20.6%for four devices at a luminance of 1000 cd m-2,respectively.These results suggest that these materials have potential application in efficient OLEDs.4.Meanwhile,we successfully synthesized four novel iridium(Ⅲ)complexes(bo)2Ir(S-tpip),(bt)2Ir(S-tpip),(thbt)2Ir(S-tpip)and(sebt)2Ir(S-tpip),using 2-phenylbenzoxazole(bo),2-phenylbenzothiazole(bt),2-thiophenebenzothiazole(thbt),2-selenophenebenzothiazole(sebt)as the main ligands and bisdiphenylthiophosphonimide(S-tpip)as the ancillary ligand.The emission peaks of these Ir(Ⅲ)complexes range from 522 nm to 613 nm and their quantum efficiency in the solution differ from 49.3%to 70.7%.The excited state lifetimes of these complexes were in the microsecond range.The device properties based on these emitters are under investigation.