Synthesis And Electroluminescent Properties Of Novel Iridium Complexes

By introducing Htpip as the ancillary ligand in the mixed-ligand iridium complexes Ir(C^N)2LX, two Iridium complexes Ir(tfmppy)2tpip and Ir(dfppy)2tpip have been synthesized and characterized with thermal analysis,1H NMR and MS along with the X-ray crystal structure analysis. Their photophysical properties were investigated in detail. In absorption spectra, the complexes show the intraligand charge transfer (π→π* (L) IL) bands and metal-to-ligand charge-transfer dπ(Ir)→π* MLCT bands. The quantum efficiency of Ir(tfmppy)2tpip and Ir(dfppy)2tpip in air-equilibrated CH2Cl2 solution are calculated to be 12.04% and 3.81%, respectively, by using air-equilibrated aqueous [Ru(bpy)3]2+·2Cl- solution as reference sample (Φstd =2.8%). The lifetime of them in powder are 0.89 and 0.77μs, respectively. In the CV spectra, one reversible oxidation process in the range of 0.60-1.20 V exists in each of the complexes which is assigned to the metal reduction/oxidation, Ir4++e-→Ir3+ The HOMO/LUMO levels are calculated as -5.44 eV/2.98 eV and -5.51 eV/-2.87 eV, respectively. Furthermore, both of them can be vacuum-evaporated easily without decomposition and show good film-forming ability. The phenomenon, showing weak phosphorescence in solution and enhanced phosphorescence emission in the solid state (EPESS), also called "aggregation-induced phosphorescent emission (AIPE)" is found in the complexe Ir(dfppy) 2tpip.To evaluate the EL performance, Ir(tfmppy)2tpip and Ir(dfppy)2tpip were used as guest materials in the fabrication of organic light-emitting devices with the structure of ITO/TAPC (40 nm)/Ir(tfmppy)2tpip or Ir(dfppy)2tpip (x wt%):mCP (20 nm)/TPBi (40 nm)/LiF (1 nm)/Al (100 nm). And the devices are named as G1 (x=4 wt%), G2 (6 wt%), G3 (8wt%), G4 (10 wt%) and G5 (12 wt%) for Ir(tfmppy)2tpip, and BG1 (x=6 wt%), BG2 (8 wt%), BG3 (10 wt%), BG4 (12 wt%) and BG5 (14 wt%) for Ir(dfppy)2tpip, respectively.At a low driving voltage of 11.8 V, the maximum luminance of 64351 cd/m2 is obtained for device G2. The maximum current efficiency (ηc) and power efficiency (ηp) are 67.95 cd/A and 69.90 lm/W, and the roll-off ratios of efficiency from the peak value (67.95 cd/A) to that at the brightness of 100 cd/m2 and from the brightness of 100 cd/m2 to 1000 cd/m2 are as low as 11.92% and 11.88%, respectively. For BG3, the maximum luminance of 38 963 cd/m2 is achieved at a low driving voltage of 11.5 V. The maximum current efficiency and power efficiency are 25.45 cd/A and 23.52 lm/W, respectively and the roll-off ratios of efficiency from the peak value (25.45 cd/A) to that at the brightness of 100 cd/m2 and from the brightness of 100 cd/m2 to 1000 cd/m2 are as low as 0.35% and 6.58%, respectively.