Synthesis And Electroluminescent Properties Of Two Red Iridium Complexes

By introducing tetraphenylimidodiphosphinate (Htpip) as the ancillary ligand, two iridium complexes Ir(tfmpiq)2tpip and Ir(dfpiq)2tpip (dfpiq=2-(2,4-difluorophenyl)quinoline, tfmpiq=2-(4-(trifluoromethyl)phenyl) quinoline) have been synthesized and characterized with thermal analysis,1H NMR and MS along with the X-ray crystal structure analysis. Their photophysical, electrochemical properties, electron mobility and electroluminescent properties have also been studied in detail. From absorption spectra in CH2Cl2solutions, the complexes show the intraligand charge transfer (π�'π*(L), IL) bands and metal-to-ligand charge-transfer (dπ(Ir)�'π*, MLCT) bands. For the emission spectra in CH2Cl2solutions, the maximum peaks are locate at622and600nm for Ir(tfmpiq)2tpip and Ir(dfpiq)2tpip, repectively, which are due to the mission of MLCT. The quantum efficiencies of Ir(tfmpiq)2tpip and Ir(dfpiq)2tpip in air-equilibrated CH2Cl2solution are calculated to be14.60%and16.64%, respectively, by using air-equilibrated aqueous [Ru(bpy)3]2+·2Cl-solution as reference sample (Φstd=2.8%). The lifetimes of them in toluene solution are0.16and0.25μs, respectively. In the CV spectra in CH2Cl2solutions, one reversible oxidation process in the range of0.40～1.60V exists in each of the complexes which is assigned to the metal oxidation, Ir3+�'Ir4++e-.The HOMO/LUMO levels are calculated as-4.80/-2.58eV and-4.73/2.57eV, respectively. The electron mobilities of two iridium complexes (Device A for Ir(dfpiq)2tpip and Device B for Ir(tfmpiq)2tpip) and Alq3(Device C) were determined via transient electroluminescence method based on ITO/TAPC/Complex/LiF/Al, driving with short, rectangular voltage pulses. The electron mobilities in60nm Ir(tfmpiq)2tpip layer are between6.61x10-6and8.49×10-6cm2/V·s under electric field from1150to1300(V/cm)1. The electron mobilities in60nm Ir(dfpiq)2tpip layer are calculated to be6.08×10-6and6.61×10-6cm2/V·s under electric field from1150to1300(V/cm)1/2. For device C, and the electron mobilities in60nm Alq3layer are calculated to be4.74～4.86x10-6cm2/V·s under same electric field. These results suggested that complexes Ir(tfmpiq)2tpip and Ir(dfpiq)2tpip have appropriate electron mobility higher than that of Alq3demonstrating they should have a better device efficiency.To evaluate the EL performance, Ir(tfmpiq)2tpip and Ir(dfpiq)2tpip were used as emitting layer material, respectively, in the fabrication of organic light-emitting diodes (OLEDs) with the structure of ITO/TAPC (60nm)/Ir(tfmpiq)2tpip or Ir(dfpiq)2tpip (15wt%):CBP (50nm)/TPBi (60nm)/LiF (1nm)/Al (100nm). And the devices are named as Al for Ir(dfpiq)2tpip, and A2for Ir(tfmpiq)2tpip, respectively.At a driving voltage of12.0V, the maximum luminance of18195cd/m2is obtained for device Al. The maximum current efficiency (%) and power efficiency (ηP) are4.71cd/A and1.82lm/W, respectively. For A2, the maximum luminance of14676cd/m2is achieved at a driving voltage of12.4V. The maximum current efficiency and power efficiency are3.47cd/A and1.51lm/W, respectively.