Sythesis And Properties Of Several Iridium Complexes

Organic light-emitting devices?OLEDs?have attracted great interest during last decades owing to their promising features,including flexibility,color tunability and low power consumption.Phosphorescent transition metal complexes have been widely used in OLEDs as the emitter because phosphors can gather both singlet and triplet excitons therefore accomplishing the theoretical 100%internal quantum efficiency.Among these complexes,iridium???complexes have been intensively studied because of their high phosphorescent quantum efficiency,short lifetime of triplet excited states and broad range of emission colors.In this thesis,several novel iridium complexes were designed and synthesized by utilizing or modifying different kinds of cyclometalated ligands or ancillary ligands,the photophysical and electroluminescent properties of which were investigated and discussed in detail.The OLEDs based on some of them performed high efficiency with low efficiency roll-off.1.New iridium complexes I-Irl to I-Ir4 using 2',6'-bis?trifluoromethyl?-2,4'-bipyridine as the main ligand and 1,3,4-oxadiazol or 1,3,4-thiadaizol derivatives as ancillary ligands were synthesized.When the ancillary ligands of 1,3,4-oxadiazol derivatives were replaced by 1,3,4-thiadaizol derivatives,the PL spectra of iridium complexes red-shifted significantly.The calculation results show that the introduction of 1,3,4-thiadiazol derivatives has effect on the contribution of the LUMOs,which contributes to the changes of the photophysical properties.The electron mobilities of the complexes were estimated by the transient electroluminescence?TEL?measurement,which are as high as that of the typically electron transport material Alq₃.The green OLED with the structure of ITO/TAPC?30 nm?/mCP?10 nm?/I-Ir2?8 wt%?:PP021?20 nm?/TmPyPB?40 nm?/LiF?1 nm?/Al?100 nm?showed high maximum efficiency(74.8 cd A^-1,EQE?external quantum efficiency?27.0%)and low efficiency roll-off(71.6 cd A^-1,EQE of 25.9%,at 1000 cdm^-2).Furthermore,the OLED performances of this series of iridium complexes were improved by optimizing the doping concentration,the thickness of emitting layer?EML?and electron transport layer?ETL?.The single-EML device based on I-Irl with the structure of ITO/M0O3?5 nm?/TAPC?30 nm?/mCP?5 nm?/I-Irl?8 wt%?:PP021?10 nm?/TmPyPB?40 nm?/LiF?1 nm?/Al?100 nm?achieved the highest current efficiency and EQE up to 86.5 cd A'1 and 31.0%,respectively.On this basis,the OLED using I-Ir3 as the emitter showed yellow emission and good perforamces(54.5 cd A^-1,16.1%).The excellent electroluminescent properties of I-Irl and I-Ir2 indicate that the usage of 2',6'-bis?trifluoromethyl?-2,4'-bipyridine main ligand and 1,3,4-oxadiazol derivatives ancillary ligand can improve the electron mobility of iridium complexes leading to high OLED efficiency and low efficiency roll-off.The comparison between the complexes with 1,3,4-oxadiazol and 1,3,4-thiadaizol derivatives as ancillary ligands suggests that the propertis can be manipulated by the substitution of ancillary ligands,which would help to find novel materials and adjust the emission color.2.Four novel iridium?III?complexes II-Irl to II-Ir4 containing 2,3-diphenylquinoxaline?DPQ?derivatives with or without fluro-substituted on different positions as main ligands and 1,3,4-oxadaizol derivatives as ancillary ligands were synthesized and thoroughly investigated.OLEDs with single-or double-EML were fabricated using ?-Ir3 and II-Ir4 as the emitters,both have higher quantum yields among these complexes.The double-EML device using II-Ir4 with the structure of ITO/MoO₃?5 nm?/TAPC?30 nm?/TcTa:?-Ir4?2 wt%,10 nm?/26DCzPPy:II-Ir4?2 wt%,10 nm?/TmPyPB?40 nm?/LiF?1 nm?/Al?100 nm?displays good electroluminescence performances with the maximum luminance,current efficiency,power efficiency and external quantum efficiency up to 20676 cd m^-2,14.0 cd A'1,12.0 lm W-1 and 17.8%,respectively.Both the double-EML devices have mild efficiency roll-off.The results demonstrate that the number and position of fluro-substitution can affect both PL and EL properties of the Ir???complexes.3.The tetraphenylimidodiphosphinate was introduced as the ancillary ligands to the deep red iridium complexes ?-Ir1 to ?-Ir4,which can improve the electron mobility of the complexes,leading to better OLED performances.All the complexes emit deep red photoluminescence with high quantum yields.OLEDs with single-or double-EML were fabricated using these new emitters.The double-EML device using?-Ir4 with the structure of ITO/MoO₃?5 nm?/TAPC?30 nm?/TcTa:?-Ir4?2 wt%,10 nm?/26DCzPPy:?-Ir4?2 wt%,10 nm?/TmPyPB?40 nm?/LiF?1 nm?/Al?100 nm?displayed better electroluminescence performances with the maximum luminance,current efficiency,power efficiency and external quantum efficiency up to 25926 cd m^-2,16.6 cdA^-1,13.71mW-1 and 19.9%,respectively,and the efficiency roll-off ratio was mild.The OLED performances were improved by the introduction of the tetraphenylimidodiphosphinate as ancillary ligands.The results suggest that these Ir???complexes are potential deep red phosphorescent materials for specific applications of OLEDs.